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University of Southampton, 2003
FACULTY OF ARTS
DEPARTMENT OF ARCHAEOLOGY
FIRESHED: THE APPLICATION OF GIS
TECHNIQUES TO HISTORIC MILITARY DATA
by Colin Lacey
A dissertation submitted in partial fulfilment of the
requirements for MSc (Archaeological Computing –
Spatial Technology) by instructional course.
‘…we shall defend our Island, whatever the cost may be,
we shall fight on the beaches,
we shall fight on the landing grounds,
we shall fight in the fields and in the streets,
we shall fight in the hills;
we shall never surrender…’
(Winston Churchill, House of Commons, 4th June 1940)
Acknowledgements
I am indebted to the following for assistance during the preparation of this
study:
Colonel (retired) David Hunt, OBE, CEng, MIEE, for providing much-needed
advice of military doctrine and fieldcraft, for leading field trips in the study area
and for devoting much of his spare time to searching for and providing data.
Mr Graeme Earl (University of Southampton), for assistance with visual basic
scripting and frequent technical queries at all hours of the day.
Dr David Wheatley (University of Southampton), for further technical
assistance, conversion of DEM and assistance with development of the
trajectory modelling system.
Dr Marcos Llobera (University of Southampton), for assistance with DEM
smoothing and trajectory modelling.
Mr Chris Webster (Somerset County Council), for provision of DEM and
photographic data.
I am also extremely grateful to my friends and family, especially Steph, for their continuing support, and for putting up with me throughout the summer of 2003.
Table of Contents Chapter 1: Introduction.........................................................................................1
Background to Military Archaeology...............................................................1 Background to GIS in Archaeology .................................................................4 Background to Anti-Invasion Defences ...........................................................5 Aim of the Study ..............................................................................................8
Chapter 2: Methodology.......................................................................................9 Software............................................................................................................9 Source Data ......................................................................................................9
Digital Elevation Model (DEM)...................................................................9 2002 Air Photos..........................................................................................11 1946 Air Photos..........................................................................................11 OS Landline Data .......................................................................................11 1929 OS Mapping.......................................................................................11 Site Data .....................................................................................................12
Selection of Area ............................................................................................13 Elevation Model Preparation..........................................................................16 Physical Properties of Pillboxes .....................................................................17
Type 24 Pillbox ..........................................................................................19 6-Pounder Anti-Tank Emplacement...........................................................21 Vickers Machine Gun Pillboxes.................................................................23
Visibility Analysis ..........................................................................................25 Viewsheds...................................................................................................27 Cumulative Viewsheds...............................................................................30 Attacks by Airborne Troops .......................................................................31 Artillery Observation Posts ........................................................................36
Fireshed Analysis ...........................................................................................48 Analysis of Anti-Tank Weapons ................................................................49 Analysis of Rifle Fire .................................................................................63 Analysis of the Bren Light Machine Gun...................................................65 Complex Firesheds: Trajectory Modelling.................................................70
Chapter 3: Discussion of Results........................................................................87 Credibility of Results......................................................................................87 General Conclusions – what the system as it stands is capable of .................89 Improvements / Future Directions..................................................................90 Conclusions ....................................................................................................95
Appendix I: Background to the Taunton Stopline..............................................97 Appendix II: Site List .......................................................................................102 Appendix III: Principles of Defence.................................................................106 Appendix IV: German Attack Tactics ..............................................................110 Appendix V: Visual Basic Complex Fireshed Script .......................................112 References: .......................................................................................................126
Table of Figures Figure 1: Planned Stoplines in Britain (C. Webster, Somerset County Council,
based on Dobinson 1996, Wills 1985) .........................................................6
Figure 2: The Taunton Stopline (Hunt Unpublished-a) .......................................7
Figure 3: A pair of buildings, digitised as vectors..............................................10
Figure 4: The same buildings converted to 10m resolution raster .....................10
Figure 5: The same buildings converted to 5m resolution raster .......................10
Figure 6: Digital Elevation Model of the study area ..........................................14
Figure 7: 1929 OS map of the study area, showing the Stopline, pillboxes and other defences.............................................................................................15
Figure 8: View restrictions – Vector above the line, 5m resolution raster below.....................................................................................................................17
Figure 9: A Type 24 Pillbox from the Taunton Stopline....................................19
Figure 10: Section of Type 24 Embrasure (adapted from Chief Engineer - Eastern Command 1940) ............................................................................20
Figure 11: Type 24 Pillbox Plan (Wills 1985:30) ..............................................20
Figure 12: 6pdr emplacement MAT 602 high on the embankment of the old Chard Canal near the aqueduct over Langport Road (Photograph: David Hunt)...........................................................................................................21
Figure 14: 6pdr emplacement MAT 604, side elevation (Wills 1985:23) .........22
Figure 15: Vickers Machine Gun Emplacement plan (Wills 1985:38) ..............23
Figure 16: Vickers Machine Gun Emplacement N17a (David Hunt) ................24
Figure 18: The visibility of a man in a hole (Drawn by L. Willoughby-Ellis)...25
Figure 19: Target heights of anti-personnel fire (adapted from War Office 1942d).........................................................................................................26
Figure 20: Testing for the intervisibility of two cells (Wheatley and Gillings 2002:205)....................................................................................................28
Figure 21: Viewshed Bounding Attributes, ArcGIS 8.3 (Drawn by S. Pillinger)....................................................................................................................29
Figure 22: Making a cumulative viewshed from three separate viewsheds.......30
Figure 23: Viewshed: Attack from the air ..........................................................33
Figure 24: A 25pdr weapon in use (Anon 1942)................................................37
Figure 25: Trajectories of guns, howitzers and mortars (David Hunt)...............37
Figure 26: Extract from Division North Artillery Plan (1940)...........................39
Figure 27: Viewsheds of incorrect and correct locations for Knapp OP............40
Figure 28: Durston OP viewshed .......................................................................41
Figure 29: Knapp OP viewshed..........................................................................42
Figure 30: Crimson Hill OP viewshed ...............................................................43
Figure 31: Viewshed of all OPs..........................................................................45
Figure 32: Dead ground from all OPs ................................................................46
Figure 33: Types of anti-tank ditch (Lowry 1996:89)........................................51
Figure 34: 6pdr Anti-Tank Gun, Royal Armoured Corps Tank Museum, Bovington (adapted from Tank Museum photograph)..............................52
Figure 35: Boys Anti-Tank Rifle (David Hunt) .................................................53
Figure 36: Vulnerable points of German tanks (adapted from VIII Corps Unknown) ...................................................................................................54
Figure 37: Screen-shot of newly-created fireshed, ArcGIS ...............................56
Figure 38: 6pdr anti-tank gun fireshed, Crimson Hill ........................................57
Figure 39: Dead ground, southwest of MAT602................................................58
Figure 40: 6pdr emplacement viewshed, Crimson Hill......................................59
Figure 41: 6pdr and Boys fireshed, Crimson Hill ..............................................61
Figure 42: Anti-tank viewshed, Crimson Hill ....................................................62
Figure 43: SMLE rifle (David Hunt)..................................................................63
Figure 44: Bren LMG (War Office 1942c) ........................................................65
Figure 45: Bren LMG on tripod (War Office 1942c).........................................66
Figure 46: Type 24 view and firesheds ..............................................................67
Figure 47: Vickers MMG (Anon 1942)..............................................................70
Figure 48: Pair of Vickers emplacements (arrowed), Crimson Hill, viewed from the attacking side (David Hunt)..................................................................71
Figure 49: Applications of Fire (War Office 1942d)..........................................75
Figure 50: Comparison between parabola and trajectory...................................77
Figure 51: SMLE trajectory plot ........................................................................78
Figure 52: Original elevation model...................................................................80
Figure 53: Distance raster reclassified into 200yd intervals .............................80
Figure 54: Previous raster reclassified with trajectory height above line of sight....................................................................................................................80
Figure 55: Result of subtracting Figure 54 from Figure 52................................80
Figure 56: Viewshed calculated using Figure 55 as DEM .................................80
Figure 57: Resulting fireshed, displayed on original elevation model ...............80
Figure 58: ‘Footprints’ of trajectories ................................................................82
Figure 59: Right angled triangles reflecting points on a trajectory ....................82
Figure 60: Calculating the angle of sight ...........................................................83
Figure 61: Complex Fireshed of MV1, Crimson Hill ........................................85
Figure 62: Theoretical and actual viewsheds, MV1, top of Crimson Hill, suggesting an enfilade role (green = theoretical arc, red = viewshed) .......86
Figure 63: Pillbox M1b, Wrantage, half excavated, illustrating the level to which it was buried to enhance its camouflage ..........................................92
Figure 64: Pillbox M1a, Wrantage, obscured by trees, indicating its height above the surrounding ground ....................................................................93
Figure 65: Overgrown and forgotten: A pillbox on the Great Western Railway, south of Creech, originally disguised as a signal box (David Hunt) ..........95
Figure 66: View from the top of Crimson Hill north towards Wrantage ...........97
Figure 67: Type 24 pillbox, Buckland, Somerset (Tacchi 2003) .......................98
Figure 69: Concrete anti-tank posts added to a railway embankment, Donyatt, Somerset ...................................................................................................100
Figure 70: Road blocks either side of a canal bridge, Donyatt, Somerset........100
Figure 71: Section of the Taunton Stopline defence plan (Crimson Hill), 1940..................................................................................................................101
Figure 72: Defending a bridge or crossing point (Mace 1996:4) .....................108
Table of Tables Table 1: Attribute Codes of 'View Restrictions' Shapefile.................................16
Table 2: Viewshed bounding attributes, ArcGIS 8.3 .........................................29
Table 3: Anti-Tank Target Heights ....................................................................54
Table 4: Target Heights for SMLE Fire .............................................................64
Table 5: Machine Gun Ranges (War Office 1937:4) .........................................72
Table 6: Trajectory Table for Rifle No 1 Mk 3 SMLE firing SAA .303 MkVII ammunition, with muzzle velocity of 2440ft/sec (War Office 1942d) ......77
1
Chapter 1: Introduction This chapter provides a basic review of the scope and background of the
archaeological study of twentieth-century military sites, outlines the principles
of the use of geographical information systems (GIS) in the discipline and
introduces the concept to anti-invasion defences in Britain. Finally, the aim of
the study is discussed.
Background to Military Archaeology Military archaeology is a global phenomenon that has only begun to be studied
in any great detail since the early 1990s (Schofield 2003:8). All work up to this
point had largely been carried out by amateurs fulfilling their own curiosity. The
end of the Cold War in 1990 brought about a change in the attitudes of the
general public toward military sites. ‘…In parallel with the work of professional
historians there has developed a lively popular interest in the physical remains
of recent warfare which are widely viewed as more immediate, local and
accessible than other machinations of politicians and higher command’
(Dobinson et al. 1997:289). For many, there is a living memory (and a degree of
sentiment) connected to their involvement in the construction and use of such
sites (Dobinson et al. 1997:289, Schofield 2001:21), although particularly for
Second World War sites, this is a dwindling resource (English Heritage 2000).
Archaeology and historical research combined are, therefore, becoming the only
sources of information for the study of military sites worldwide, putting them in
line with more ‘conventional’ forms of archaeology.
The Defence of Britain Project exemplifies this amateur-professional
relationship. This was a project set up by the Council for British Archaeology in
April 1995, which invited members of the public to submit site reports of all
kinds of Britain’s surviving military architecture. The final submission date was
in autumn 2001 and the project has resulted in an online searchable database of
military sites, hosted by the Archaeological Data Service. This provides a record
of approximately 20,000 surviving sites of the hundreds of thousands built
(including some 5,500 surviving pillboxes including many of those in the study
area, all built in the latter half of 1940 (Foot 2003:8).) Defence of Britain
records were also submitted to local Sites and Monuments Records (SMRs) and
2
the National Monument Record (NMR) – an action which has, in itself,
instigated a great deal of interest in the subject (Schofield 2003:5).
Following the completion of the Defence of Britain Project, the Project’s co-
ordinator, William Foot, has been commissioned by English Heritage’s
Monuments Protection Programme to create local studies of anti-invasion
landscapes, using 1940s defence plans from the Public Record Office, Kew, the
physical remains and 1946 aerial photographs to record the most coherent and
legible defence landscapes surviving from the 1940-42 period. This two-year
study, known as the ‘Defence Areas Project’ is being carried out in order to
assess structures for preservation, either individually or in collective local
groups (Foot 2003:9). It does not, however, draw on the SMR ‘Officers’ or
other local sources of information; neither does it exploit any GIS analysis.
Likewise, David Hunt, a retired colonel, is carrying out an in-depth study of the
Taunton stop-line (a highly defended inland ‘frontier’, designed in 1940 to
contain any German invasion of the SW peninsular of England). Despite the
level of examination that has been carried out, Schofield’s framework highlights
the need for study ‘with a view to further understanding defence policy and its
implementation at a local level, and set within the national context’ (in press).
John Schofield (Head of Military and Naval Evaluation Programmes, English
Heritage) identified that ‘a GIS-based work to combine strategic ideals and
military doctrine with reality (through viewshed and field-of-fire analyses)’ was
in need of investigation..” in his forthcoming English Heritage research
framework, ‘Modern Military Matters’ (in press). The present study was carried
out on his personal recommendation to fill the gap left in previous research.
Schofield invited David Hunt to contribute to the forthcoming research
framework and at his suggestion, Hunt was asked to support the writer of this
dissertation with both his knowledge of anti-invasion defences gained through
his in-depth research and his specialist military knowledge and experience. This
includes assignments as a Weapons Technical Staff Officer, formal staff
training at the Royal Military College of Science (Army Staff Course Division
I), The RAF Staff College and the German Armed Forces Command and Staff
College. Support took the form of teach-ins, and observations expressed below
are those of the author unless credited.
3
Military archaeologists face a number of challenges in their work. Defence
works were often constructed with great haste under the threat of an enemy
attack at any time and consequently, the records kept are frequently patchy –
that is to say when the records can be found – the British armed forces are not
known for keeping classified documentation until long after its useful life has
ended. Premature destruction of records is also a common occurrence. Although
there is still a surviving element of those that remember World War II first-
hand, those that remember the particular object of the archaeologist’s studies are
frequently difficult to find. Also, the factor that many people, particularly those
with bad experiences of the War, whilst having useful memories, are more
inclined to believe that they are best forgotten. This attitude also percolated
through local and national government and led to the large-scale removal of
World War II archaeology as soon as its use had passed. Despite this, there is
still a great deal to be learned from these relics of one of the tensest periods of
Britain’s recent history. In 1944, once the Allied forces had established
themselves on the Continent, permission was given to start removing anti-
invasion defences across the UK (Hunt 2003).
Challenges particular to the study of anti-invasion defences are also common.
Few senior officers with experience of, and responsibility for the construction
works survive. Few records of their ‘appreciations of the situation’ and reasons
or justifications for decisions taken exist. Anti invasion was a completely new
situation for the Army with new roles to fulfil and considerable overstretching
of resources. The totally unexpected situation post-Dunkirk left the country with
no preparation or contingency plans against a new threat. Britain as an island
nation did not have the history or experiences of a land-based frontier with
permanent fortifications, in contradiction with those of Belgium, France and the
Netherlands. All work was carried out under constant threat of invasion forcing
short cuts to be taken or non- optimal solutions adopted to ensure that, if the
invasion happened, there would be some fortifications for the defenders.
Mistakes were made and documentation was often not produced. Some
fortifications, removed at the end of the war and after, cannot now be surveyed
to establish orientations, fields of view and fields of fire. (Hunt Unpublished-a).
4
Background to GIS in Archaeology GIS … are computer systems whose main purpose is to store, manipulate,
analyse and present information about geographic space.
(Wheatley and Gillings 2002:9)
From the 1970s, heralding the early days of GIS in archaeology (Wheatley and
Gillings 2002:18), there have been many great developments in technology,
both hardware and software based. Modern GIS, with their easy-to-use
graphical user interfaces, and pre-coded macros, used to automate both
frequently-used and complex features and carry out far more than is possible
with a paper map alone. Currently, archaeologists use GIS in many ways.
Simple uses include spatial databases – the foundation for all systems, but often
used alone, in their own right, as three-dimensional data storage media, able to
store, and most importantly, display, the locations as well as the attributes of a
feature. One main use of GIS in archaeology is to take this a step further and ask
why these features are located where they are. Analysis of factors ‘outside the
artefactual sphere’ (Wheatley and Gillings 2002:17) – geology, political
boundaries and effects of natural phenomena such as sunlight and rainfall all
affect the location of, for example, settlement sites, and all can all be modelled
using GIS. A step further still is into the realm of spatial patterning. The use of
GIS to determine whether archaeological site location is random or organised,
based on natural or cultural phenomena, is a common field of study (see for
example Hodder and Orton 1976) This leads into fields such as cost-surface
analysis (e.g. Bell and Lock 2000) and predictive modelling of site location –
using characteristics of known sites to predict the locations of those currently
unknown (see Warren 1990). Increasingly in recent years GIS has become
accepted as an essential tool to Cultural Resource Management as a way to store
and analyse details of significant sites on a regional basis (Wheatley and
Gillings 2002:19).
The archaeological use of GIS exploited in this study is visibility analysis – the
ability of a point to ‘see’ other points. This is explained in greater detail below.
5
Background to Anti-Invasion Defences After the German conquest of France in June 1940 Britain
was alone and in imminent danger of German invasion.
(Alexander 1998)
Immediately following the withdrawal of the British army from Dunkirk in late
May 1940, Britain was the closest it had been to being invaded for centuries.
Since the previous conflicts in the nineteenth century, technology had advanced
to such an extent that Britain’s once formidable coastal defences were now
inadequate against the advanced, highly mobile weaponry of the twentieth
century. The development of the aeroplane, faster ships and the most feared of
new weapons, the tank, meant the risk to the country was dramatically
increased. Immediately the withdrawal from Dunkirk was complete, on
approximately June 4th (Green and Plant 2003), General Sir Edmund Ironside,
Commander in Chief of Home Forces, gave the order for the most intense
period of military construction in England for centuries, and the construction of
‘the largest system of defensive earthworks ever built in England’ (Foot
2003:9).
The concept was simple – to create defended lines, or ‘stoplines’ across the
country that would ‘block the progress of armoured columns, setting them up
for a counter-attack… A stopline would [be] a continuous anti-tank obstacle,
natural if possible, covered by pillboxes and other prepared positions’ (Green
and Plant 2003). ‘Soldiers recently returned from France laboured alongside
civilian workers to build concrete gun-posts and pillboxes for the nations few
remaining weapons’ (Alexander 1998:9).
The immediate object is to divide England into several small
fields surrounded by a hedge of anti-tank obstacles which is
strong defensively, using natural accidents of the ground where
possible. Should Armoured Fighting Vehicles or airborne attacks
break into the enclosures the policy will be to close the gate by
blocking the crossing over the obstacles and to let the ‘dogs’ in
the shape of armoured formations, or other troops, in to round
up the cattle.
(Southern Command 1940)
6
Britain’s main stopline was constructed, running from the west coast of England
to the east, below London, then turning north and stretching to Edinburgh and
beyond. This line was known as the General Headquarters Anti-Tank Line
(GHQ Line) and consisted of a continuous stretch of natural features, anti-tank
obstacles, roadblocks and bridges prepared for demolition should the need arise.
The line was punctuated with pillboxes and gun emplacements – ‘hardened
defence works’ (Foot 2003:8) – of varying sorts, which, using the limited
weaponry available in the aftermath of Dunkirk, were intended to destroy the
attacking force as they became stuck at the anti-tank obstacles. Field artillery
and even anti-aircraft units, which were mobile and had no permanent structures
built for their use, would support pillboxes. Several more stoplines were
constructed in areas to the south and west of the GHQ line, in order that an
attacking army would have to break through several lines before being able to
take control of the country.
Figure 1: Planned Stoplines in Britain (C. Webster, Somerset County Council, based on Dobinson 1996, Wills 1985)
7
‘In principle the General Headquarters Line bore the
unmistakable stamp of linear and frontal defensive lines
established in France during World War One. Unfortunately
many of the weapons available to defend the fortifications of the
General Headquarters Line including ex naval guns, machine-
guns and rifles also dated from the same period.’
(Alexander 1998:9-10)
The Taunton Stopline was a World War II anti-invasion stop line, facing west,
built between July and November 1940. Its aim was to ‘stop an enemy’s
advance from the West and in particular a rapid advance supported by
Armoured Fighting Vehicles (up to the size of a German medium tank) which
may have broken through the forward defences’ (War Office 1940).
Figure 2: The Taunton Stopline (Hunt Unpublished-a)
For a more detailed description of the Taunton Stopline, see Appendix I.
The fronts are everywhere. The trenches are dug in the towns
and streets. Every village is fortified. Every road is barred.
(Winston Churchill, BBC Broadcast, 14th July 1940)
8
Aim of the Study To investigate how GIS-based terrain analysis can contribute to the study
military defences in Britain by using as an example World War II anti-invasion
defences on a selected section of the Taunton Stop Line in South-west England.
Nothing of this kind has previously been carried out for this period of Britain’s
history and it is thought that these important sites from our recent past should be
given the same consideration as is currently being given to more ancient sites. It
should also be noted that the majority of the techniques developed during this
study are also applicable to the archaeological study of weaponry and defences
of all ages – from the Roman fort, ballista and bow-and-arrow, to the motte-and-
bailey castle or classical fortifications such as vauban, the trebuchet and the
cannon, the main differences lie in the scale and weapon properties.
9
Chapter 2: Methodology This section explains the technical aspects of the study, beginning with the
specifications of the software and source data used. The selection criteria for the
area of study are described, as is the procedure of re-working the terrain model
to include features that obstruct the view of an observer. The next section
describes how the physical properties of the types of pillboxes found in the
study area affect their fields of view and fire. Visibility analysis is next covered,
with sections covering observation of attacking parachute troops and the
determination of artillery observation points from somewhat ambiguous
documented locations. Following on, ‘fireshed’ – the devised system of
analysing fields-of-fire of the various weapons on the Stopline – is described in
two forms – flat and curved trajectory weaponry. Each weapon is introduced,
after which the procedures for calculating its fireshed are described, along with
analyses of sample results.
Software The majority of work was carried out using ESRI ArcGIS 8.3 (hereon in
referred to as ArcGIS). Image format transformation was carried out using Corel
Photopaint 11.
Source Data Source data for the project consisted of ESRI shapefiles, raster images, ESRI
grid datasets, and Microsoft Excel spreadsheets. Below, the source data and its
particulars are listed:
Digital Elevation Model (DEM) Description: Raster digital elevation model (DEM) of the county of Somerset.
Point data in 10m grid, Z values obtained from photogrammetry.
Origin: Purchased by Somerset County Council from a third party air-
photo and photogrammetry company.
Processing: Data was compiled from a point text file using ArcGIS, in which,
data for the study area was cropped from the rest of the county.
The resulting data was smoothed using a 6x6 mean filter, due to
regular microtopographical anomalies giving a regular tartan-like
pattern to viewsheds. Finally, the data was resampled from 10m
10
resolution to 5m in order that digitised buildings and hedgerows
measuring less than 10m across were displayed correctly (see
below).
Uses: The DEM was used as a terrain model for viewshed and fireshed
calculation. Photogrammetry data is now considered a ‘viable
alternative to the use of map-based elevation data’ (Wheatley and
Gillings 2002:113).
Figure 3: A pair of buildings, digitised as vectors.
Figure 4: The same buildings converted to 10m resolution raster
(raster = green, vector = blue)
Figure 5: The same buildings converted to 5m resolution raster
(raster = purple, vector = blue)
11
2002 Air Photos Description: 0.25m resolution colour raster images of the study area in
ERMapper ECW format.
Origin: Purchased by Somerset County Council from a third party air-
photo and photogrammetry company.
Processing: None
Uses: Establishment of accurate locations of pillboxes (where still
extant) and ease of navigation and visualisation of the landscape.
1946 Air Photos Description: Incomplete 0.25m resolution monochrome raster images of the
study area in ERMapper ECW format.
Origin: Somerset County Council. Originally taken as reconnaissance
photographs by the Royal Air Force soon after the end of the Second World
War.
Processing: None
Uses: Establishment of accurate locations of pillboxes (where visible –
camouflage was still in good condition in many cases) and ease
of navigation and visualisation of the landscape. There were
many gaps in the 1946 coverage (often in important areas).
OS Landline Data Description: Fully feature-coded vector data of Ordnance Survey 1:2500 scale
mapping.
Origin: Ordnance Survey
Processing: Cropped to study area and converted to shapefiles using ArcGIS.
Uses: Establishment of accurate locations and orientations of pillboxes
(where still extant) and ease of navigation and visualisation of
the landscape.
1929 OS Mapping Description: 0.21m resolution raster data of 1929 Ordnance Survey mapping.
12
Origin: Somerset County Council digital data and University of
Southampton Cartographic Unit map archive sheet maps.
Processing: Digital data was in georeferenced Tagged Image Format (TIF)
and it was decided that, to reduce image size, the images would
be converted to Portable Network Graphic format (PNG) and TIF
world files (TFW) were renamed as PNG world files (PGW) to
preserve georeferencing. Paper maps were scanned using an A4
flatbed scanner, again into PNG format, then georeferenced and
georectified using standard tools in ArcGIS.
Uses: Ease of navigation and visualisation of the landscape prior to the
construction of the Taunton Stopline.
Site Data Description: Details of pillboxes, gun emplacements and crossing points
(SMR number where applicable, grid reference, site description,
designation and site type, bearings where applicable) stored in a
Microsoft Excel spreadsheet.
Origin: Pillbox data from Somerset County Council Sites and
Monuments Record (SMR), crossing points selected from OS
maps as points at which tanks and troops could cross canals,
railways and other physical boundaries forming part of the
stopline (i.e. bridges), compiled by David Hunt as part of his
research into the stopline. Bearings for some sites taken in the
field using magnetic compasses and from air photos / OS
Landline maps
Processing: Excel files converted to shapefiles using ArcToolbox, a facility
of ArcGIS.
Uses: Pillboxes and gun emplacements used as sources for viewsheds
and firesheds, and crossing points used as targets for gunfire, as
the enemy would be ‘funnelled’ into a confined space at these
points.
13
Selection of Area In order to test viewshed and fireshed techniques, a sample area of the Taunton
Stopline was required. An area measuring 6km (E-W) x 8km (N-S) was chosen
on the basis that:
• It featured each of the three main types of pillbox (and therefore all of
the main types of weapons) used on the Stopline.
• There is a high survival rate of pillboxes and accurate locations are
available for those removed.
• Its terrain is highly varied, ranging from 4m to 110m (heights above sea
level), also containing canals and railway cuttings, woodland and
buildings, and consequently is better suited for demonstrating the effect
of terrain on view and fire than a flat piece of ground. Particularly
interesting is Crimson Hill, a large plateau in the southeast corner of the
study area with a steep wooded scarp face dropping from it to the north.
This features several pillboxes aimed out across the steep wooded
hillside.
• Full DEM, 1929 map and 2001 air photo cover, and good 1946 air photo
cover is available in a georeferenced digital format from Somerset
County Council.
• The landscape has changed relatively little since the Second World War.
14
Figure 6: Digital Elevation Model of the study area
15
Figure 7: 1929 OS map of the study area, showing the Stopline, pillboxes and other defences
16
Elevation Model Preparation The digital elevation model of the area had been ‘cleaned’ when produced: Due
to the nature of air photos depicting everything visible at ground level, the DEM
would have initially recorded woodland, hedges, buildings and other articles
standing above ground level as ground level. These features were removed
before the model was supplied to customers. Unfortunately, visibility and field-
of-fire analysis requires that these ‘artefacts’ are present. In order to get around
this problem, woodland, thick hedgerows and some buildings were digitised as
polygons in a shapefile, using the editing tools of ArcGIS. Locations for the
above were obtained largely from 1946 air photos, although for gaps in this
coverage, estimates were derived from a combination of both 1929 OS maps
and 2001 air photos. The attributes of each polygon were coded as to the type of
view restriction they represent using the following table: 1
Code Description Height (m) 1 Woodland 30 2 Thick Hedgerow 1.7 3 Building 10 4 Possible Woodland 30 5 Possible Hedgerow 1.7 6 Possible Building 10 7 Crimson Hill Scrub 1
Table 1: Attribute Codes of 'View Restrictions' Shapefile
Finally, the shapefile was converted (using ArcGIS Spatial Analyst conversion
routine) into a 5m resolution raster dataset containing the height values. This
was added to the elevation model using the ArcGIS Raster Calculator, with the
resulting raster becoming the basis for all future calculations.
This method was chosen above digitising features directly as rasters, due to its
flexibility – it is possible to manipulate polygons and change their values far
more and with less effort than when working with rasters alone.
1 Heights of hedges, scrub and buildings were estimated from modern examples. Modern tree heights were measured using basic trigonometry and averaged giving the approximate height of 30m.
17
Figure 8: View restrictions – Vector above the line, 5m resolution raster below.
Physical Properties of Pillboxes Essentially, a pillbox is a reinforced building in which troops can shelter from
incoming fire and retaliate with their own weapons. Described as ‘probably the
most familiar type of 20th century defensive building’ (Lowry 1996:79), these
structures provided the backbone of defence along the Taunton Stopline. They
were situated both to directly defend vital crossing points and to deter attacking
armies from their task. Designs were issued by branch FW3 of the War Office
Directorate of Fortifications and Works in June 1940 for around twelve types of
pillbox, which were loosely adhered to by regional construction workers (Lowry
1996:79). Three main types of pillbox can be found on the Taunton Stopline.
The most common is the Type 24 thick-walled (shell-proof2) hexagonal pillbox
(also the most common in Britain (Foot 2003:8)). Second is the Vickers
machine gun emplacement and third, the six-pounder anti-tank gun
emplacement – a design specific to the Taunton Stopline. Each pillbox is
characterised by its role, usually governed by the weapon it is designed to hold.
2 The 1936 Army Manual of Field Engineering stated that 3’6” (1.67m) of reinforced concrete would resist a 6” (15.2cm) shell (Alexander 1998:88).
18
This also dictates the shape and size of its loophole or loopholes3 which were
wherever possible, ‘sited to provide interlocking fields of fire with other
pillboxes over the anticipated directions of attack, and designed to minimise
external dimensions, so limiting access to incoming fire, whilst maximising
freedom of movement internally for the weapon and its operator’ (Lowry
1996:79). Another factor of the loophole was that it restricted the vision of those
inside the pillbox, both vertically and horizontally. It is this factor that is
important for the analysis of fields of view and fire.
3 Loopholes – firing loops, embrasures – splayed horizontal slits for looking or firing through (Lowry 1996:79).
19
Type 24 Pillbox
Figure 9: A Type 24 Pillbox from the Taunton Stopline
The type 24, also referred to as an ‘FW3 / Type 24’, is a hexagonal pillbox with
five large loopholes suitable for Bren light machine guns and Boys anti-tank
rifles, each with a ‘table’ formed from the thickness of the wall, on which the
bipod of the weapon would stand. The fifth wall, slightly longer than the others,
featured a central doorway flanked by a single rifle loophole on each side. These
were somewhat cruder in form than the other loopholes and did not have the
luxury of a table for tripod-mounted guns. Tables as such were only provided in
Vickers emplacements, whereas Type 24 boxes had slots built under the
loophole to accommodate the front leg of the tripod of a Bren Light Machine
Gun or a Boys Anti-Tank Rifle. The doorway was situated to the ‘safe’ side of
the stopline (see Figure 9 above) and the rifle loopholes were intended for local
defence only. Internally, the posts featured a ‘Y’ shaped baffle wall to contain
ricochets and blast from incoming fire.
20
Figure 10: Section of Type 24 Embrasure (adapted from Chief Engineer - Eastern Command 1940)
Each main loophole had an arc of fire of approximately 60°, meaning that
allowing for the small gaps between the rifle and main loopholes, type 24
pillboxes could cover almost 360°, and the non-covered area (‘dead ground’)
was entirely behind the stopline, so not of great concern. Vertical restrictions of
view were calculated using the original construction plans (Chief Engineer -
Eastern Command 1940) taking the vertical centre of the loophole as the
observer height. Details of the measurement can be seen in Figure 10 above.
Figure 11: Type 24 Pillbox Plan (Wills 1985:30)
6-Pounder Anti-Tank Emplacement
Figure 12: 6pdr emplacement MAT 602 high on the embankment of the old Chard Canal near the aqueduct over Langport Road (Photograph: David Hunt)
These emplacements were originally open concrete-walled pits as described by
Alexander (1998:92), although at a later date, rear walls (on the ‘safe’ side of
the stopline) and roofs were added to give the gun crew a greater level of
protection from shelling and dive
bombers. The gun was situated on a
pedestal forward of the wall and
could swing through a 180° arc,
which was also the field of vision of
the personnel. It is assumed that
there are no practical restrictions on
elevating the gun to fire up to its
designated range of 600yds or
depressing the gun to engage targets
within its arc of fire (Hunt 2003).
Vertical restrictions on view, dictated
by the presence of the front wall and
Figure 13: Pedestal in MAT 602
(David Hunt)
21
22
roof (see Figure 12 above and Figure 14 below), are considered minimal as the
gun crew are able to move to the front of the emplacement and look upwards
past the roof and downwards past the wall.
Figure 14: 6pdr emplacement MAT 604, side elevation (Wills 1985:23)
23
Vickers Machine Gun Pillboxes
Figure 15: Vickers Machine Gun Emplacement plan (Wills 1985:38)
These pillboxes were characterised by their square shape and a single large
embrasure with a large concrete table inside, where a Vickers machine gun
would stand on its tripod. The boxes also featured two rifle loopholes for local
defence, situated in the walls opposite and to the left of the main embrasure
(when viewed from outside, facing the main embrasure), and in the wall to the
right, a doorway shielded by a separate large concrete blast wall. It should be
noted that pillbox NV15 is unique in that it has two large embrasures, on
adjacent walls. Only one table is present, and it is thought that the embrasure
24
with the table would be used in preference to the other. In all calculations,
therefore, the additional embrasure is analysed separately.
Figure 16: Vickers Machine Gun Emplacement N17a (David Hunt)
Again, the embrasure restricts the view and fire from inside as follows:
As with the Type 24 pillbox above, the rifle loopholes
placed to defend the stopline but are for local defenc
have been ignored in view and field-of-fire calculations
Figure 17: Restrictionsimposed by VickersEmplacement embrasure(adapted from Wills1985:38)
are not a strategic feature
e only. Due to this, they
.
25
Visibility Analysis Reconnaissance is as important in the defence as in the attack.
Active patrolling should be carried out, and the enemy kept
under constant observation by forward infantry posts and
intelligence sections. By the piecing together of small items of
information which in themselves may appear unimportant, the
enemy’s intentions may often be deduced.’
(War Office 1937:145)
The key to the defence and attack of an area is visibility. Opposing sides both
want to see as much of their adversaries as possible, without being seen
themselves. Due to this factor, the terrain can be both an ally and an enemy to
the soldier. It can provide elevated observation points and areas to hide where
the landform masks the view from the observer. These areas in which observers
cannot see their enemy, are known as ‘dead ground’. The level of dead ground
decreases the higher above ground level the subject of observation stands. For
instance, a man crouching in a one meter deep hole may be invisible to the
observer, although when the same man, measuring for instance, 1.6m, stands in
the same hole, the upper 0.6m of his body is visible.
Figure 18: The visibility of a man in a hole (Drawn by L. Willoughby-Ellis)
(green = invisible, red = visible)
26
The technology of warfare in the 1940s meant that there were several levels of
observation desired by the defending force. Observation to ground level – if
anything is present, at any height, it will be seen. Observation to approximately
one metre – the height of a man kneeling or crawling / running whilst bent
double, and the height of the top of the tracks of a tank, meaning the entire hull
of the vehicle is visible. Observation to 1.6m – the height of a standing man and
the turret of a tank (known as ‘hull down’ – i.e. the turret is the only part
visible). Observation to two metres – the top of the turret of a tank – if
approaching over the brow of a hill, the tank commander would raise a flap in
the turret and examine the view over the hill. Alternatively, periscopes would be
used, protruding from the turret This is known as ‘turret down’. Finally,
observation to 91m (300 feet) – incoming parachute troops and dive-bombers.
Figure 19: Target heights of anti-personnel fire (adapted from War Office 1942d)
Even when out of range of weaponry, those defending need a view of the enemy
as soon as possible, in order to get some idea on the direction of forthcoming
attack, and to plan the counter-attack wisely. Moreover it is vital that all
positions along the forward defended localities maintain all-round observation
to gather intelligence and to avoid being surprised by the enemy.
Two main scenarios illustrate this concept and are outlined below: attack by
parachute and artillery observation. The former is a theoretical scenario,
applicable to other defences, but outlined here in principle, and the latter uses
methods described to calculate the likely location of points referenced poorly in
contemporary documents. The military have been estimating fields of view for
many years, by use of the map contours or by drawing cross sections or profiles
of the terrain using physical pen-and-paper methods using contours from maps
as source data (Hunt 2003, War Office 1937:110-11).
27
An attacker would be looking for:
i. Covered approaches, Close or wooded country will offer
special opportunities for a concealed advance and for
outflanking or surprising the enemy.
ii. Positions from which observed covering fire can be brought
to bear.
iii. Features which when occupied or captured will enable to
enemy’s position to be enfiladed and a flank attack to be
made under favourable conditions.
iv. Ground favourable for the co-operation of armoured fighting
vehicles.
v. Probable lines of advance of hostile tanks and the areas in
which hostile tank counter-attacks are likely to be made.
vi. A line of attack by which the advancing troops will be
defiladed as far as possible from enemy weapons.
vii. Facilities for concealment from hostile aircraft.
(War Office 1937:111)
Manual calculation of fields of view and fire is a laborious and time-consuming
exercise that, with good quality GIS software, and a fairly powerful computer,
can be automated into a procedure that takes seconds.
Viewsheds Both scenarios above can be modelled using a common application of GIS in
archaeology – visibility analysis. For many years, the technique of analysing
points that can be seen from other points (viewshed analysis) is widely used in
the planning and civil engineering industries and widely in the modern military
(Fisher, P 1991:1321). Visibility analysis is also by no means a recent
development in archaeology. Well before the advent of GIS, antiquarians, and
later, archaeologists were making basic observations about spatial patterning
and site location (Wheatley and Gillings 2000:1). Further applications were
initially developed in the 1970s, documented by Hodder and Orton (1976) and
Renfrew, in his 1979 report containing analysis of the visibility and
28
intervisibility of prehistoric sites on Orkney. The GIS-based study of visibility
escalated considerably in the 1990s with the development of viewshed analysis
(Wheatley and Gillings 2002:201). Traditionally, viewshed analysis has been
largely restricted to the study of prehistoric archaeology, and it is not thought
that it has been used (in an archaeological sense) on anything as recent as World
War II, although it is at least as useful to this relatively modern period as it is to
the neolithic.
Viewshed calculations in this study use the digital elevation model as prepared
above, and a list of points, as source data. The points represent the observer
points and are automatically assigned an elevation value corresponding to that
of the underlying pixel of the DEM. The calculation that produces the viewshed
is best described by Wheatley and Gillings as follows: ‘…for each cell in the
raster, a straight line be interpolated between the source point and every other
cell within the elevation model. The heights of all the cells which occur on the
straight line between the source and target cells can then be obtained in order to
ascertain whether or not the cell exceeds the height of the three dimensional line
at that point’ (2002:205).
Figure 20: Testing for the intervisibility of two cells (Wheatley and Gillings 2002:205)
Upper example – cell is visible. Lower example – cell is invisible.
The result is a raster dataset in which pixels are coded with the following values
– 0 for invisible from observer point (or in this case, ‘dead ground’) and 1 for
visible. ArcGIS allows the constraining of viewsheds in several ways. Angles
29
and heights can be added as fields to the attribute table for each entry in the
observer point dataset and are as follows:
Attribute Name Description Default Value SPOT Assigns absolute elevation to observer
point (overwriting DEM value) No default
OFFSETA Vertical distance to be added to DEM value at observer point
0
OFFSETB Vertical distance to be added to DEM value at target point
0
AZIMUTH1 Anticlockwise horizontal angle limit of viewshed calculation
0
AZIMUTH2 Clockwise horizontal angle limit of viewshed calculation
360
VERT1 Upper vertical angle limit of viewshed calculation, measured from the horizontal
90
VERT2 Lower vertical angle limit of viewshed calculation, measured from the horizontal
-90
RADIUS1 Inner radius of viewshed area – calculations only occur beyond this distance
0
RADIUS2 Outer radius of viewshed area – calculations do not occur beyond this distance
Infinity
Table 2: Viewshed bounding attributes, ArcGIS 8.3
Figure 21: Viewshed Bounding Attributes, ArcGIS 8.3 (Drawn by S. Pillinger)
30
Cumulative Viewsheds Cumulative viewsheds are a simple sum total of individual viewsheds,
calculated on a pixel-by-pixel basis:
1 0 1 1 0 0 2 1 0 1
+ 0 1
+ 0 1
= 0 3
Figure 22: Making a cumulative viewshed from three separate viewsheds
The resulting raster contains a value per pixel that relates to the number of observer points able to see that pixel. ArcGIS calculates cumulative viewsheds automatically without calculating the individual viewsheds.
31
Attacks by Airborne Troops ‘Parachute troops were dropped from about 300 feet from
aircraft and gliders… Their morale was very low unless
they had time to organise after landing. When attacked at
once they were easily disposed of… Small arms fire against
descending parachute troops was only effective at short
range. The lessons for the Home Guard [and other
defending soldier] in this include:-
(a) Parachute troops must be attacked at the earliest
opportunity. Every second counts in making your plan
and carrying it out. Every moment lost will cost you
lives and ammunition. Risks must be freely taken in
order to gain time. The enemy must be sought out and
destroyed.
(b) You must not wait for parachute troops to attack you.
(c) Memorise covered approaches to all points in your
area where they may land.
(d) If possible prevent them from reaching their arms
containers; the weapons they carry on them are only
short range, so you can snipe them while you are out of
their range…’
(Langdon-Davies, on the German invasion of Crete, and
how it applies to the defence of Britain (1942))
This section uses viewshed analysis to evaluate how the physical constraints of
pillboxes affect the areas in which incoming airborne assaults can be seen at a
height of 300’ (91m).
It can be seen from the training advice given above that the impetus was on
elimination of attacking forces immediately (or prior to) the moment at which
their feet touch the ground. This relies on the knowledge that troops are being
dropped by parachute, which stems from the defending force seeing the
parachutists whilst airborne, or the aircraft from which they are to be dropped.
32
Equally, gliders should be seen on their landing approach glide. As the Vickers
machine gun was primarily an anti-personnel weapon, and due to the
complication of range finding on targets that are not at ground level, together
with the unsuitability of the tripod mounting and sights to track fast moving
aerial targets, making it unlikely that the gun would have been used in such a
way (War Office 1942a makes no reference to attacking aircraft with the
Vickers Machine Gun), it is feasible that it would have been used against just-
landed paratroopers or gliders.
The ability to see such troops or gliders as they descended would be crucial to
the process of aiming and setting the range of the gun on the landing ground to
engage the enemy with fire. Likewise, the ability to descend out of view of the
waiting guns could be a significant benefit to the attacking force. It should be
noted, however, that there is no evidence to suggest that the Taunton Stopline
design was influenced by such factors (Hunt 2003). Nevertheless, the study has
been included to demonstrate the potential. An example where the technique
could be particularly valuable would be in the analysis of highly successful
attacks by glider borne troops on the Belgian Fortress of Eben Emal in May
1940 (Bierganz and Heeren 1990).
Viewsheds produced with OFFSETB values of 91m (300’) will therefore
indicate the points at which the gunner will be able to see his descending targets
and set up to give them a hostile welcome. It was with this in mind that the
viewshed, Figure 23 overleaf, was created.
33
Figure 23: Viewshed: Attack from the air
It is of interest to note the arc of dead airspace lying in front of the pillboxes
caused by the vertical restrictions of the embrasures. The Vickers emplacement
has a fairly large opening, therefore the view at 300’ from such a building is far
greater than would be possible from the smaller embrasure of a Type 24. The
34
increasing depth of red shading, illustrating areas with less emplacements able
to see the area is a useful tool in predicting areas with decreased risk to
parachutists, although caution must be exercised here – this may be an artefact
of ‘edge effect’ – the non-inclusion in GIS calculations of emplacements lying
beyond the edges of the study area, which still have influence over it.
Also worthy of mention is the patch of dead ground to the west of NV18 and
NV19 (to the left of the image). This area is shielded from view by an area of
woodland, highlighted in a deep red indicating its visibility from some eight or
nine gun emplacements. If it had been the case that the area was only defended
by the Vickers machine guns, this would be an area in which parachutists could
be successfully landed without fear of being spotted (whether or not the aircraft
dropping the soldiers would be visible, is a different matter, beyond the scope of
this example). This conclusion emphasises the importance of negative data in
military archaeology.
‘Dead ground’ - where a defender cannot observe – is a benefit to the enemy,
and likewise, ground that cannot be seen by the enemy is a benefit to the
defender. In this latter case, it might allow the defenders to supply their
positions, move up reinforcements in ‘covered approaches’ or to prepare further
positions or obstacles out of view of the enemy on the ground. The term ‘dead
ground’ is obviously relative to a particular observation point. What a soldier on
the ground cannot see is in ‘dead ground’ to him but it may be clearly visible to
an observer in a high building and therefore not in ‘dead ground’ to the latter.
These techniques are as valid for the study of a medieval castle or Iron Age
hillfort as to the study of the more recent past.
Returning to the matter in hand, it is evident that the modelling technique
described above also works with Type 24 pillboxes and anti-tank gun
emplacements, which, whilst not necessarily equipped as well as a Vickers
emplacement to deal with such an attack, would have been able to fire on
paratroops with light machine guns from within the pillbox or rifle from the
troops outside, so would also have been appreciative of forewarning and a view
of the sky. This technique of analysis is better suited to other anti-invasion
defences such as those on airfields, although their absence in the study area
dictates the use of Vickers emplacements to demonstrate this technique, also
35
valid for use on anti-aircraft guns, searchlight sites and radars. The concept
could also be used to indicate the range at which low-flying reconnaissance
aeroplanes and other enemy aircraft would have come into view over the terrain.
Dive-bombers such as the Stuka, had an exceptionally steep angle of attack
against targets and are therefore unlikely to have been shielded by terrain in
their high altitude approach run, before diving steeply onto their chosen target
(See also Langdon-Davies 1942: Section XII: Anti-Aircraft).
The analysis of Second World War airborne attack scenarios using viewshed
techniques has been proven to be very successful. The presence and absence of
vision in a defensive situation are incredibly useful factors to the historian and
archaeologist alike, and their use is most definitely not restricted to the study of
the Second World War.
36
Artillery Observation Posts ‘In some instances, visibility can be regarded as a key factor in attempting to
answer the question as to why a particular site is in a particular place, rather
than all the other places it might have been located’
(Wheatley and Gillings 2002:202)
Whereas in other disciplines of archaeology, site location often depends on
many factors, ranging from proximity to water and food, to distance from
symbolic sites, military sites are often chosen only for one – visibility.
Soldiers defending the Taunton Stopline would not all have been posted in
pillboxes, defending the immediate frontier. Situated behind the line would be
artillery batteries designed to bring heavy fire down on attacking forces from a
distance.
Each of the six brigades earmarked for deployment along the Taunton Stop
Line, was to be supported by a Field Artillery regiment consisting of two
batteries. Each battery consisted of twelve weapons (Hunt Unpublished-a) – a
mixture of 18pdr guns and 25pdr howitzers. In artillery terminology, a gun is a
weapon with a high muzzle velocity, which can fire over a long range, with a
comparatively flat trajectory whereas howitzers have less of a muzzle velocity
but a very high trajectory (see Complex Firesheds below for further definitions
of military terms).
‘The gun has a longer range and a more rapid rate of fire than a
howitzer of corresponding classification; the howitzer has a
greater shell power and the ability to search ground behind
cover, which guns owing to their flat trajectory cannot reach.
Howitzers can be brought into action almost anywhere, e.g.
directly behind steep ground, buildings, or woods; positions for
guns are much harder to find, since it is necessary to ensure that
their flat trajectory will clear the crest of any high ground or
obstacle between gun and target (this factor is known as “crest
clearance”).’
(War Office 1935:10)
37
Figure 24: A 25pdr weapon in use (Anon 1942)
Figure 25: Trajectories of guns, howitzers and mortars (David Hunt)
When used in a defensive situation, the Field Service Regulations manual (War
Office) gives the following roles for the application of artillery weaponry:
i. Counter-preparation – fire directed on the enemy’s forming-
up places and forward communications, so as to disorganise
and, if possible, break up an attack that appears to be
imminent.
ii. Defensive fire – against troops engaged in an attack, usually
targeted at pre-arranged areas, in coordination with other
weapons (i.e. the Vickers Medium Machine Gun in the
Taunton example), on a pre-arranged signal [for example a
38
rocket or ‘Verey’ light – see also War Office Tactical Notes
for Platoon Commanders (1941)].
iii. Anti-Tank defence – a second line of fire if enemy tanks
breach the front line.
iv. Counter-battery – fire directed at enemy artillery.
v. Harassing fire – to hinder progress in attack and destroy
attacker’s morale by preventing or hampering movements of
reinforcements, food and ammunition to the front line.
As artillery batteries were situated behind the line, often out of direct sight of
the enemy, there were limitations to the effectiveness of the weaponry in all of
the scenarios above if observation and communication was poor. To combat this
factor, observation posts (OPs) were established on high ground at some
distance from the guns to act as the eyes of the gunners. Each battery could
deploy one OP but may temporarily deploy a 'subsidiary OP' to cover areas not
visible from the main OP. In addition, the excellent communication of the OP
(compared with those of a 1940 infantry battalion) would have enabled it to
rapidly pass valuable intelligence rearwards up the chain of command (Hunt
Unpublished-a).
The Roles of Artillery Observation Posts (from War Office 1939)
1. Observation and control of artillery fire
2. Study tactical situation
3. Pass information about enemy and own troops to higher
command
The importance of the OP is highlighted in the Field Service Regulation manual
in that ‘If the enemy can be actually seen attacking, they will be engaged with
defensive fire by all batteries whose observers can see them, although the pre-
arranged signal [see ii. above] may not have been given… Since artillery is
normally placed in indirect positions… the selection of …OPs and the
establishing of communication between the OPs and the guns is often the
determining factor in the time taken by artillery to open fire’ (War Office
1935:12-13). Note that, provided both the gun position and the position of the
target are accurately known, it is possible for the guns to engage the target with
a ‘predicted shoot’. Wherever possible, an OP would adjust such fire onto the
target.
Documentary evidence for the artillery OPs on the stopline is vague when
giving locations – the surviving document (Division North 1940) mentions 1/25,000 sketch maps, although these have not survived. In the same document,
each OP is given a general location and a list of points it can see. This is
currently the only known evidence for the study area OPs (Note that the grid
references relate to the wartime Cassini grid and not the Ordnance Survey
National Grid):
(B) Brigade. Battery. O.P. Visibility from O.P. No. 1. 2 O.Ps North Approaches to obstacle about & South of 1 mile North & South of road at DURSTON. DURSTON. No. 2. KNAPP. From DURSTON to NEW BARN 7345. (C) Brigade. Battery. O.P. Visibility from O.P. No. 1. CRIMSON HILL From STONY HEAD 7344 to
northern slope CRIMSON HILL.
39
Figure 26: Extract from Division North Artillery Plan (1940)
A trial-and-error process was used to suggest accurate locations for these OPs,
using a combination of OS map data, air photographs and the DEM. The
elevation model was examined for the highest ground at each locality. The area
was checked for suitability using maps and air photographs (i.e. the elevation is
not ‘falsely high’ due to the presence of woodland or post-1940s structures or
earthworks), and if considered viable, a point was created and a 360° viewshed
calculated with an observer height (OFFSETA) of 1.6m, to account for a man
standing. This was compared with the Division North Artillery Plan (Figure 26
above) for conformity. When the viewshed was not sufficient to cover the areas
mentioned, another point was chosen and the procedure repeated until sufficient
results were found.
40
Figure 27: Viewsheds of incorrect and correct locations for Knapp OP
In addition, the resultant viewsheds were modified to reflect the distance from
the OP on the basis that the further the point was from the OP, the less easy it
would have been for the observer to identify camouflaged troops or to identify
hostile activity. This was carried out using ArcGIS Spatial Analyst. A ‘distance
to…’ calculation was used to produce a raster in which each cell contained its
distance from the OP. The viewshed, being a binary dataset (0 = invisible, 1 =
visible) was multiplied pixel by pixel, by the distance calculation using the
raster calculator. This resulted in the same distance raster cropped to only the
visible cells of the viewshed. All other cells had a value of zero. In displaying
the resultant raster, it was possible to use this classification (i.e. to use a
graduated fill, the level of which depended on the pixel value, or to create bands
of colour for certain distances) or to display it as a conventional viewshed, using
one colour for a value greater than one4. The distance viewsheds can be
interpreted in one further way – as indicating towards the quality of view. The
further away something is, the less clarity it has, even when viewed through
binoculars. For this reason, the following viewsheds of the estimated positions
4 It is not possible to calculate a cumulative viewshed from this using the
conventional technique, and for this reason, it is recommended that the original
viewshed is retained.
41
of the OPs are displayed with green fading to red. Green indicates good clear
vision, whereas red indicates a deteriorated view due to the longer distance.
Figure 28: Durston OP viewshed
42
Figure 29: Knapp OP viewshed
43
Figure 30: Crimson Hill OP viewshed
One final image was produced using a cumulative viewshed from all OPs. This
is to show dead ground (areas invisible to observers). When studying defence
works, negative data is as important as positive data. Dead ground is ground in
which the enemy can hide from the view of the observer, be it for
reconnaissance, to group before an attack, or to rest after fighting. Dead ground
44
is a risk to the defending troops. Whereas all dead ground behind the stopline
can be ignored, there are some glaring holes in the cover on the non-defended
side. The area southeast of the Crimson Hill OP, flanking the northern side of
the Crimson Hill ridge, is an ideal corridor for attackers to use in order to get
close to the Stopline. Again, a corridor running right up to the line can be seen
0.5km south of Lillesdon. There are also significant areas of dead ground to the
southwest corner of the study area in which large armies could assemble unseen
in readiness for an assault on the Stopline. Whether an enemy could have
identified these covered approaches from the map or by reconnaissance, is
another matter. Nevertheless, they clearly indicate points where the OP could
not observe and report movement or engage with artillery fire.
45
Figure 31: Viewshed of all OPs
46
Figure 32: Dead ground from all OPs
It should be noted that many of these areas of dead ground, especially those
close to the line, would have been covered by fire from pillboxes and gun
emplacements on the line itself. No one aspect of the defences was intended to
operate alone, and mutual support between permanent and mobile units would
have ensured any gaps were well covered. Also worthy of note is that an OP
47
was located at Beer Crowcombe, just southeast of the study area, which was
intended to cover the large area of dead ground on the plateau to the east of the
Crimson Hill scarp round to Ashill.
In a defensive position, fields of fire should normally overlap (War Office
1941), and the areas where there is the greatest overlap may give some
indication of where the planners of the defences considered the threat to be
greatest. Conversely, where the overlapping is minimal or non-existent, it may
identify areas where the perceived threat was lower or there were simply
insufficient troops available to cover it. In this case, examination of viewsheds
may show whether the area of weakness could be observed so that a patrol
could be sent out to intercept the enemy or artillery fire directed onto the
attackers. Here the artillery observation viewshed might give an indication as to
whether the Artillery OP would be able to observe the enemy movement and
call down fire and direct it onto the target.
A GIS such as this can therefore be used to help accurately predict the location
of poorly defined observation posts, providing the terrain model is accurate for
the time period under consideration (see Fisher, P 1991). It gives an excellent
indication of where artillery OP could observe the enemy, report their
movements and engage with artillery fire and, equally important, the areas
where this would not have been practical.
48
Fireshed Analysis A major part of this study was the formation of a methodology for modelling
the theoretical fields-of-fire of the various weapons used on the Taunton
Stopline in a 1940 anti-invasion defence scenario. Due to the reliance of the
methods developed on viewshed calculations, this analysis has been entitled
‘fireshed’. A fireshed indicates the areas that the field-of-fire for a given
weapon at a given point will cover (i.e. a specific target can be engaged by the
given weapon).
Two types of fireshed analysis were developed, each applying to weapons with
particular characteristics. Simple firesheds were developed for weapons that are
fired only at targets that can be seen. Complex firesheds were developed for
weapons fired at targets that are not in a direct line of sight, but can still be hit
providing the coordinates of the target are known (indirect fire – see War Office
1937:5).
49
Analysis of Anti-Tank Weapons ‘The weak points of the German tank are six in number.
(a) Its Blindness. The only view obtainable is through the
driver’s slit, the gunner’s slit, and the commander’s
slit, all of which are very cramped, or the periscope
which can be smashed with small arms fire.
It cannot see anything above itself… It cannot see the
ground anywhere within fifteen feet of itself… In order
to increase visibility tanks often move with the lid open.
(b) Field of Fire. The tank’s guns cannot be lowered to
shoot anything on ground level within twenty feet of the
tank, and they cannot be raised more than twenty-five
degrees upwards… Tanks’ gun-turrets revolve very
slowly and their weapons defend the vehicle from
attack only along their immediate line of sight. Attack,
therefore, from several points at once, must find gaps
in the tank’s defence.
(c) The Tracks. The tank is only useful so long as it can
move: and it can only move so long as the tracks work.
The tracks are very easily broken, and for this reason
anti-tank attacks should usually be concentrated on
breaking the tracks.
(d) Inside the Tank. The living conditions inside the tank
are cramped, very hot, and therefore very exhausting.
No tank crew can remain for more than a few hours
inside a closed tank… If tanks can be kept under
observation… there is bound to come a time when the
crew have to come out; and then they are very easily
destroyed.
(e) Petrol. The tank is, of course, entirely dependent upon
its petrol supplies. These are often brought with it in
50
petrol lorries, which can be easily set on fire with
proper ammunition…
The tank must be prevented at all costs from any
chance of refuelling by the wayside…
(f) Night. Darkness is the greatest ally of the tank hunter.
As night approaches tank crews seek harbours where
they may lie up and rest. This is the opportunity for
stalking, sniping and attacking with grenades and
incendiary bombs.’
(Langdon-Davies 1942)
Whilst the obstacles of the Taunton Stopline were designed to stop the progress
of tanks, it would not destroy them, and would effectively leave a row of enemy
guns pointed at the defending force. Tanks needed to be destroyed, and for this
purpose, anti-tank guns were employed.
As can be seen from the quote above, a tank is similarly restricted both in vision
and fire to a pillbox. The latter has the advantage that it can be easily hidden
until needed, and that the gun crew know the terrain in advance, and the former
has the overwhelming advantage that it is mobile. It is much harder to hit a
moving target, particularly one moving ‘tactically’ so that it makes the best use
of any cover offered by the terrain.
The passage of tanks throughout the countryside would have been made
difficult by the use of many ‘passive’ defences such as anti-tank ditches and
obstacles, and roadblocks. These would funnel tanks into areas in which they
could be attacked easily by troops defending the line. Anti-tank guns were
situated primarily on the main routes of passage or to cover areas where the line
was considered weak.
51
Figure 33: Types of anti-tank ditch (Lowry 1996:89)
Static anti-tank guns on the Taunton Stopline were primarily the 6-pounder
6cwt Mk II Hotchkiss static-mounted ex naval gun (6pdr). These were
reconditioned First World War naval guns of the same variety used in the Mk I
Tank, also of First World War vintage, mounted on specially made steel
pedestals inside covered concrete pits (6pdr emplacements). ‘Every gun was
52
supplied with 50 rounds of ammunition and a crew of 2 Non Commissioned
Officiers (sic) and 8 Gunners organised to be self-contained in an emergency
with at least 4 days hard rations’ (Alexander 1998).
Figure 34: 6pdr Anti-Tank Gun, Royal Armoured Corps Tank Museum, Bovington (adapted from Tank Museum photograph)
These guns were capable of firing beyond 8000yds (7315m, Royal Armoured
Corps Tank Museum pers. comm.) although for maximum accuracy 6pdrs on
the Taunton line were restricted to firing on targets within a range of 600yds
(549m) as the ‘first shot must be a hit and fire must be withheld until a hit is
certain…’ (Southern Command 1940). In order to locate a tank before it came
into range, and to identify it as hostile, gun crews needed to be able to see
further than this. Up to a range of 600yds, a 6pdr trajectory was for all intents
and purposes, flat and had a reasonable probability of hitting the target provided
that the gun sights had been set to the appropriate range. Anti-tank guns were
always only used in direct fire, where the gunner could see and ‘lay on’ the
target. Thus, calculation of a fireshed for a 6pdr emplacement does not require
any consideration of the trajectory. A viewshed with the desired target height
(OFFSETB) is calculated, cropped to a radius (RADIUS2) of 549m.
The second weapon used on the Taunton Stopline, capable of attacking
armoured vehicles, was the Boys 0.55” Anti-Tank Rifle. These were
specifically designed, with a firing rate of nine rounds per minute (War Office
1942b), to combat German tanks developed at the end of the First World War,
but was found less effective against the newer, thicker-armoured tanks used by
the enemy in the late 1930s and 1940s. Each infantry battalion should have had
between 17 and 21 Boys Rifles but many were lost in the May 1940 withdrawal
53
from Dunkirk. Despite their lack of penetrating power, ‘from very close range,
firing from a predetermined firing position in a pillbox, the Boys was still quite
a deterrent against thin skinned armoured cars forced to a halt by road-blocks
and anti-tank ditches’, and despite its growing obsoleteness, ‘it was still the
only reliable anti-tank weapon the infantry could hope to have at hand’
(Alexander 1998). Again, to ensure maximum penetration on the vulnerable
parts of the tank, the range at which infantry were told to limit their fire was
300yds (274m – War Office 1942b). Calculation of a fireshed for a Boys rifle
does not require any consideration of the trajectory and is also very
straightforward. The procedure is the same as dictated for the 6pdr above,
although the RADIUS2 value is restricted to 274m.
Figure 35: Boys Anti-Tank Rifle (David Hunt)
Tank target zones
Approximate ‘kill zones’ (i.e. where to hit the tank to be sure of immobilisation
and / or destruction) of World War II German tanks were located generally
around weak points in the fabric of the vehicle. A guaranteed immobilising
move is to remove one track, thus the tops of tracks and the track return rollers
are prime targets for anti-tank fire, but an immobilised tank (or ‘M-Kill’) can
still fire on the defences. Other points include the turret ring , where the turret
rotates on the hull, areas in which the armour is thinner, or where existing
openings can be found (i.e. around protruding guns, engine and hull air intakes).
These were more likely to result in destruction of the tank or a K –Kill. A
contemporary British diagram illustrates them thus:
54
Figure 36: Vulnerable points of German tanks (adapted from VIII Corps Unknown)
Based on this information, anti-tank firesheds are calculated with target heights
as listed in Table 3, below.
Target Height (OFFSETB, in
m) Description
0 Anything from ground level up – all of the tank would be vulnerable
1 The top of the tracks (main target zone) to the top of the turret – main vulnerable points all covered
Table 3: Anti-Tank Target Heights
55
Anti-Tank Fireshed calculation procedure in ArcGIS:
Produce viewshed from axis of gun with the following settings (assuming
standard Taunton Stop Line gun emplacement – for non-standard designs,
values will require recalculation.
6pdr emplacement:
AZIMUTH1 = [axis of fire] - 90
AZIMUTH2 = [axis of fire] + 90
OFFSETA = [height of gun barrel in m] = 1.6
OFFSETB = [target height – see Table 3]
VERT1 = [maximum elevation of gun barrel from
horizontal] = 90
VERT2 = [minimum elevation of gun barrel from
horizontal] = -90
RADIUS2 = [maximum permitted range] = 549
Boys emplacement:
AZIMUTH1 = 0
AZIMUTH2 = 360
OFFSETA = [height of gun barrel in m] = 1.35
OFFSETB = [target height – see Table 3]
VERT1 = [maximum elevation of gun barrel from
horizontal] = +5
VERT2 = [minimum elevation of gun barrel from
horizontal] = -5
RADIUS2 = [maximum permitted range] = 274
The resulting raster displays the fireshed from static anti-tank gun positions.
56
Figure 37: Screen-shot of newly-created fireshed, ArcGIS
57
Analysis of Anti-Tank View and Firesheds
Figure 38: 6pdr anti-tank gun fireshed, Crimson Hill
As can be seen from Figure 38 above, the Wrantage area either side of the
current A378 (in 1940 the B3153) had very good 6pdr anti-tank coverage at 1m
target height. The great deal of overlap between guns MAT603 and MAT604 on
the flat, open ground on the Crimson Hill plateau give an impermeable area in
which each gun can support the other if under attack. A large area of dead
ground is apparent below the Crimson Hill scarp face. This is less of a problem
than it seems, as tanks would have been totally unable to climb the steep face or
58
traverse laterally along the hillside in this area due to its steep topography and
dense woodland.
Figure 39: Dead ground, southwest of MAT602
The main weak point demonstrated is the patch of dead ground stemming from
farm buildings, leading southwest away from MAT602, at the foot of the hill
(Figure 39). Analysis of the viewshed of these sites (Figure 40), shows that this
corridor is up to 0.5km wide in places and runs approximately 2km to a large
band of dead ground lying parallel with the Stopline which could easily be used
as a hidden passageway right to the defences by an attacking army. Of
consolation is the fact that the northeast limit of this dead ground, on a bend in
the road, two guns have overlapping arcs of fire. The close range to the
pillboxes at this point would also place the tank in a very vulnerable position as
it can only engage one target at a time. Tanks never advance alone for this very
reason (Hunt 2003). At this time, the gun not being aimed at by the tank can
destroy the vehicle. Defences should normally be sited to allow mutual support
59
between the pillboxes containing the weapons (i.e. one pillbox is able to fire on
enemy directly attacking the other) and these techniques enable this principle to
be tested (War Office 1941).
Figure 40: 6pdr emplacement viewshed, Crimson Hill
On the negative side, a single tank would never attempt to breach the line alone
and those following behind will a) be able to see the location of the 6pdr
emplacement when it fires on the first tank, and b) be in a position to retreat
quickly to the dead ground area and plan its retaliation. This would no doubt
60
result in a close-quarters direct-fire fight, which, it is thought, the 6pdr
emplacements could not win (Hunt 2003).
However, it is not the case that 6pdr emplacements would be fighting alone in
defending the Stopline. Adding to the equation the view and firesheds of the
neighbouring Type 24 pillboxes, with their Boys anti-tank rifles, the situation is
greatly improved. It can be seen from the images below that the only significant
ground dead to fire is that of the Crimson Hill scarp face, which is not passable
by tank, although the viewshed with a target height of 2m (the top of a tank)
shows that a tank anywhere on the ‘dangerous’ side of the stopline would have
been visible, and able to be tracked until within range of the guns.
In the example of the Taunton Stopline, it should be noted that the German
army was highly skilled in massing armoured vehicles once they found
opposition that they could neither rush through nor bypass. They would use
sheer volume of armour to punch through the line, as the presence of a great
many simultaneously moving targets would overwhelm the small number of
6pdr and Boys guns in the area. Tanks would move in tactical bounds between
points of dead ground, with one troop or squadron covering the other as they
advanced at top speed to the next patch of dead ground. A good defence system,
therefore, covers most, if not all, of the dead ground. Coupled with this intensity
of armoured attack, Stuka dive-bombers would have attacked gun
emplacements (hence the concrete canopies erected for 6pdrs). See Appendix
IV for a background to German attack tactics.
Overall, it can be seen that the modelling of viewsheds and firesheds of anti-
tank weaponry can give a good insight into the strengths and weaknesses of the
defensive position and assist in deducing the possible strategy of a defended
area. It must be remembered that ideal circumstances rarely exist and most
defensive plans are a compromise. The examples above show that where gaps in
cover by one kind of weaponry exist, they may well be covered effectively by
another, making a significantly better ‘tank stop’ (to use the 1940 terminology)
to invading tanks, that might otherwise be unnoticed by the archaeologist or
historian.
61
Figure 41: 6pdr and Boys fireshed, Crimson Hill
62
Figure 42: Anti-tank viewshed, Crimson Hill
63
Analysis of Rifle Fire
Figure 43: SMLE rifle (David Hunt)
Developed in the 1890s, the Short Magazine Lee Enfield rifle (SMLE) was the
standard service rifle of the British Army during both World Wars. It used the
standard .303 cartridge format, also used in the Bren Light Machine Gun and, in
a somewhat modified form, in the Vickers Medium Machine Gun. The role of
the SMLE on the Taunton Stopline was entirely anti-personnel. The rifle would
be fired from infantry slit-trenches and from pillboxes, such as the Type 24. It
was not normally to be used as an offensive weapon from the loopholes of the
Type 24, as the soldiers were dug in around the pillbox (War Office 1941), as
the loopholes offering the best arcs of fire were occupied by the Bren Light
Machine Gun (LMG) or Boys Anti-Tank Rifle.
Calculating SMLE Firesheds
The SMLE was, like the 6pdr and Boys rifle, a weapon fired directly – i.e. only
at visible targets. Its fireshed, therefore, is calculated along the same lines as for
the aforementioned weapons, by producing a cropped viewshed. In order to
obtain a reasonable maximum range of fire, rifle range target data was obtained
from ‘Small Arms Training Volume I, Pamphlet 1’ (War Office 1942d) which
stated that a first-class shot can hit a 12” (30cm) diameter target consistently at
a distance of 200yds (183m). Taking an estimate of the width of a man’s chest
at 18” (45cm), simple mathematics dictate that the same first-class shot could
hit a man consistently at 300yds (274m). This was later confirmed in Pamphlet
3 of the above series, which instructs that a rifle should not normally be used at
a range greater than 300yds on a moving human target.
In order to calculate a SMLE fireshed in ArcGIS, guidelines should be followed
as for Boys rifles, detailed above, with the following modification:
RADIUS2 = 274
64
In addition, as the weapon was used in an anti-personnel role, its target heights
varied from that of anti-tank weaponry, as can be seen in Table 4.
Target Height (OFFSETB, in
m) Description
0 Ground level – target is 100% vulnerable to fire 1 Man crawling, or running in a crouched position
1.6 Man standing Table 4: Target Heights for SMLE Fire
Firesheds for SMLE rifles along the Taunton Stopline are incorporated in a general Type 24 fireshed, which can be found on page 67.
65
Analysis of the Bren Light Machine Gun
Figure 44: Bren LMG (War Office 1942c)
The Bren Light Machine Gun (LMG) was introduced to the British Army in
1938 and used the same .303 calibre rounds as the SMLE rifle. The gun was
mounted on a bipod (Mk 1 guns featured telescopic legs) and was to be used
(subject to availability following Dunkirk) in every Type 24 pillbox on the
Taunton Stopline, as an anti-personnel weapon (see also Fisher, R 2003 for a
history of the Bren LMG).
The Bren LMG, like the Boys Anti-Tank Rifle, the 6pdr Anti-Tank Gun and the
SMLE rifle, was a direct fire weapon. Although the sights could be set to 2000
yds (or 1800 yds – Mk II gun) it had a recommended range of 600yds and a
maximum practical range of 1000yds (549m and 914m respectively – Hunt
2003).
The Type 24 pillbox was primarily designed to protect the Bren LMG or Boys
Anti-tank rifle. Each of the 5 forward loopholes was provided with a slot to
accommodate the front leg of the Bren tripod. The Bren, when mounted on the
tripod, had an arc of fire that was restricted to 38° – much narrower than the 50º
permitted by the Type 24 loophole (War Office 1942c).
66
Figure 45: Bren LMG on tripod (War Office 1942c)
1. There are five tripods for LMGs to each infantry company; one
with each platoon, the other two with company headquarters
for allotment to platoons as required. Normally tripods are
used only in defence.
2. The use of the tripod is twofold :-
i. To enable the gun to fire on a fixed line.
ii. To enable it to fire within the limits of a fixed arc.
Apart from these uses, the gun will normally be fired from the
bipod, because of the far greater flexibility with which it engage
targets in different directions when thus mounted. (War Office
1942c)
Areas of dead ground between the arcs of fire from adjacent pillbox loopholes
exist, although each pillbox is unlikely to have been manned by more that a
couple of LMG. It was commonplace to remove the gun from the pillbox and
set it up close by, in order to cover this dead ground (War Office 1941). The
five-metre resolution of the DEM dictates that in order to affect the view and
firesheds produced, the gun when arranged thus, would need to be in a separate
cell from the pillbox, which could be up to five metres away. For this reason,
all-round coverage is assumed from the pillbox site. Viewsheds are calculated
on the same basis as for the SMLE rifle, with a RADIUS2 value of 914m.
67
Figure 46: Type 24 view and firesheds
The above fireshed was produced by creating a cumulative viewshed of Type 24
pillboxes on the Taunton Stopline, ignoring those forming part of anti-tank
islands as these were a later addition in 1941. The viewshed had a target height
(OFFSETB) of 1m and a RADIUS2 value of 914m (the maximum practical
68
range of a Bren LMG, and the general area of interest of the infantry soldiers
with both Boys and SMLE rifles Hunt). In order to display a banded result, a
distance calculation (see Complex Firesheds below) was also carried out on the
points. The viewshed was reclassified using ArcGIS Spatial Analyst into two
classes: 0 = 0, >0 = 1. This process converted the cumulative viewshed, with
values reflecting the number of pillboxes able to see the point, into a simple,
visible or invisible classification, and when multiplied by the distance
calculation, as for the creation of ‘quality of view’ viewsheds, resulted in a
raster in which every pixel of visible ground contains its distance from the
nearest pillbox. This raster was cropped to exclude data on the eastern side of
the line. The raster was displayed with its distances up to 300yds / 274m
coloured green, up to 600yds / 549m coloured yellow and the final band, up to
1000yds / 914m, coloured red.
In the green band, all weapons are effective. This is also the only band in which
tanks are vulnerable, due to the presence of the Boys rifle. Enemy Infantry are
also exposed, as they are susceptible to fire from both the SMLE rifle and the
Bren LMG. The yellow band indicates the usual operating range of the Bren,
and the red, the maximum range of the Bren and the area of interest for
observation by troops in or around Type 24 pillboxes.
Immediately apparent from the fireshed is the large (0.5km wide) gap in the
green band mid-way along the southern arm of the stopline. This gap is out of
range of Boys rifles, meaning it is easily permeable by tanks, unaffected by the
smaller calibre weapons that do cover the area. A similar, although smaller, gap
exists 0.25km east of Lillesdon, and a larger gap can be found at the northern
limit of the study area at Durston. Here, lying just beyond the northern boundary
of the study area, a 6pdr anti-tank gun stood which would most probably cover
this sufficiently. The former two gaps, however, are ideal for the attackers to
penetrate and double back to destroy the surrounding pillboxes from their
vulnerable side (see Appendix X for details of German attack tactics, and War
Office 1937:109-10 for British tactics in the same situation).
Also apparent are patches of dead ground, especially in area north of Lillesdon.
Some of these form corridors along which tanks and infantry could advance
unseen. In general, excepting this dead ground, there is good anti-personnel
69
cover to be found all along the line in the study area, although the Crimson Hill
plateau appears to be weakly covered. Again, overlapping cover from pillboxes
situated outside the study area may cover this ground, and the Vickers machine
guns also situated here to the south of Beer Crowcombe would enhance the
defence a great deal.
A point worthy of note is that this fireshed is not accurate around Lillesdon, in
that it would be impossible to obtain a direct line of fire through the hamlet due
to the presence of buildings, which would significantly reduce the viewshed at
this point. An area for future work is in digitising every building in a study area,
and measuring and assigning accurate heights to said structures. Also absent is
tree cover along the canals that form the main obstacle. Air photos failed to
reveal the density (and in some cases, presence) of trees along much of the
length of the canals, and therefore they were not digitised.
Despite these inaccuracies, this does prove that calculating firesheds for direct-
fire weapons is possible using viewshed techniques, and, given accurate
elevation data, the method can be applied to many situations throughout time.
70
Complex Firesheds: Trajectory Modelling Modelling ballistic trajectories using GIS viewshed techniques has never before
been documented. This study is breaking new ground with the development of a
technique intended to analyse the fields of fire of historical weaponry in a three
dimensional, geographical nature. The technique is applicable to any projectile-
launching weapon of any period, providing range tables such as Table 6 below
are present or can be produced.
The method is ultimately useful for the modelling of firesheds of weapons used
in ‘indirect fire’ – that is to say firing at points the gunner cannot see. This could
be, for example, on ‘fixed lines’ or ‘fixed arcs’ through fog, smoke, or at night
provided preparation has been carried out in daylight (War Office 1937:4). The
only infantry weapon, capable of indirect fire, used in permanent fortifications
on the Taunton Stopline was the Vickers Medium Machine Gun. The Bren
LMG when mounted on its tripod could be fired against targets temporarily
obscure by fog, smoke or darkness but could not practically fire against targets
outside its field of view.
A more complex case is where the target is hidden behind the crest of a hill and
the weapon has to fire over the crest. The weapon obviously has to know where
and when a potential target appears if it to attempt to engage it. The field
artillery supporting the garrison of the line would normally have fired from
concealed gun positions in the indirect mode against targets that could not be
observed from the gun. This analysis has only been applied to the Vickers
MMG as no accurate locations for artillery batteries are known.
The Vickers Medium Machine Gun
Figure 47: Vickers MMG (Anon 1942)
71
The Vickers Medium Machine Gun (MMG) was ‘the most powerful of all
infantry weapons in defence’ (War Office 1937:4). Introduced in 1912, the
MMG was a large, belt-driven gun, capable of firing up to 250 rounds in one
minute (War Office 1937:5). The gun had a variety of mounts, the most popular
being a tripod (Forty 1998:24) on which it stood atop a concrete table in the
Vickers emplacement, with its ammunition and a water canister used for cooling
the barrel, beside it (Alexander 1998:93). The guns were located in pairs along
the stopline as a section of two guns shared a range-finder and fire controller,
usually situated in a slit-trench between the two emplacements (Hunt 2003).
Figure 48: Pair of Vickers emplacements (arrowed), Crimson Hill, viewed from the attacking side (David Hunt)
Vickers MMG ranges were defined as in Table 5 below. Close range fire was
easily directed and somewhat economic in terms of ammunition. Beyond this, a
far greater deal of accuracy and rigidity in control is required in order to
guarantee successful fire. Effective and long ranges both require a greater
amount of ammunition in order to be sure of hitting the target. Above all, it was
important to accurately know the range of the target being engaged.
72
Term Range (yards) Close <800 Effective 800 – 2000 Long 2000 – 2800
Table 5: Machine Gun Ranges (War Office 1937:4)
The introduction of Mark VIIIz streamlined ammunition just before the Second World War enabled the gun to engage targets to 4200 yards (Hunt 2003). Before fireshed calculation methods are discussed, military terminology relating
to general small arms and more specifically to machine guns is listed to aid in
the understanding of further sections.
Small Arms Terminology (Adapted from War Office 1942d)
These terms have been in military use in Britain throughout the twentieth
century. Similar terms are used in other countries.
Line of fire – direction of target from muzzle of weapon.
Line of sight – straight line from firer’s eye through the sights to point aimed at.
Trajectory – curved path taken by bullet during flight.
Culminating point – greatest height above line of sight to which the bullet rises
in flight.
Angle of descent – angle that the tangent to the trajectory makes to line of sight
at point of impact.
First catch – point where bullet has descended sufficiently to strike the top of
the target
First graze – point where bullet, if not interfered with, will first strike the
ground.
Dangerous space – for a given range, is distance between first catch and first
graze. See below.
Tangent angle (or tangent elevation) – angle that barrel axis makes with the line
of sight.
Angle of sight – angle between line of sight and horizontal plane.
73
Crest Clearance Angle – angle by which axis of gun barrel must be raised above
line of sight to crest to ensure all bullets clear the crest.
Quadrant elevation – angle between barrel of gun and horizontal, always above
the angle of sight (see also War Office 1942a).
To summarise; the Dangerous Space depends on the:
• Range
• Height of weapon above ground level
• Height of object fired at (target)
• Flatness of trajectory
• Conformation of ground
The Dangerous Space decreases as the range increases, due to steeper angle of
descent at longer ranges.
The Dangerous Space increases:
• The nearer the weapon is to the ground
• The higher the target object
• The flatter the trajectory
• The nearer the ground conforms to the angle of descent of the bullet
Note that with a gun firing at a set range over flat ground, the bullets should
strike the ground at that range.
Machine Gun Terminology (Adapted from Hunt Unpublished-b, War Office
1942a)
Cone of Fire – When fire is delivered to a target, the bullets pass through the air
in the shape of a cone of fire which is the pattern formed by a series of shots
fired with the same elevation and point of aim. (e.g. Bren LMG – cone of fire is
oval pattern with density decreasing from the centre outwards. Approx size at
500 yds is 6.5 ft W x 7.5 ft H for bursts fired from bipod and 3.5 x 5.5 ft for
bursts fired from tripod.)
74
Beaten Zone – When machine gun fire is correctly applied to a target, the bullets
of the cone on striking the ground form a beaten zone around the target. The
size of the beaten zone will vary with the range and slope of the ground in
relation to the angle of descent of the bullets. Beaten zone depth increases with
range due to increased angle of descent. Beyond 1500yds it increases again;
particularly laterally but, at the same time, the angle of descent becomes steeper
and the dangerous space formed by the lowest bullets of the cone becomes
smaller. (e.g. Bren LMG – at a range of 500 yds, the beaten zone measures
172yds in length by 2yds in width. At a range of 1000 yds, the beaten zone
measures 115yds in length by 4yds in width.)
Effect of Ground on Beaten Zone – A cone of fire striking a steep hillside will
cover a very small area of ground. As the slope decreases, the beaten zone
increases. The maximum occurs when the slope of the ground in the target area
conforms to the trajectory of the bullets. In some cases, the ground may slope
away out of sight of the firer (i.e. a ‘reverse slope’) but still be covered by the
beaten zone. Troops in this ‘reverse slope’ position would be unseen by the firer
but would still be in danger of un-aimed fire from the Bren LMG or indirect fire
from the Vickers MMG.
Permissible Error In Ranging – The error that can be made in range estimation
while still keeping the target in the beaten zone. The centre of the beaten zone
should be centred at the range of the target. The permissible error is therefore
half the beaten zone. As the distance increases, it becomes increasingly
important to establish the accurate range to the target.
Defiladed Zone – The area of ground that would be in the beaten zone but for
the fact that a proportion of the bullets of the cone have met an obstruction,
usually a piece of high ground.
Dangerous Zone – For fire to be effective, the target must be included in the
dangerous zone, which is the area of the beaten zone plus the dangerous space
formed by the lowest bullets of the cone.
75
Figure 49: Applications of Fire (War Office 1942d)
It is, therefore, vital that modelling of the dangerous zone be carried out in order
to assess the effectiveness of, or reason behind, the placing of a weapon. As
essentially, the dangerous zone is defined by the trajectory, this is what is
modelled below.
Roles of the Machine Gun (Adapted from Hunt Unpublished-b)
1. To fire at point targets. (The gunner needs to see the target and to
accurately know the range; particularly at longer distances)
2. To fire on fixed lines producing a long thin fixed 'fence' of fire that will
kill anything walking across the fixed line. Typically the fixed line
might be along the obstacle (e.g. a canal) or down an approach road.
(Here the trajectory matters a lot as at the far end of the line, the attacker
will be shot in the foot, while at the centre of the fixed line, they will be
shot through the head).
3. ‘Sweeping terrain with fire’ so that any soldier moving across that
terrain is likely to be hit. (With this technique, the gun sights are set at
one range (normally 600yds) in the knowledge that the dangerous space
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is such that a man at any lesser range should be hit). This technique
might be used to deny attackers access to particular areas.
4. To put down a weight of fire on a particular area (e.g. a bridge as a
‘crossing point’ over an obstacle). Here the main effect is the beaten
zone. Outside the zone, towards the gun, there will also be the
‘dangerous space’, which depends on the terrain, range and height of
trajectory above the actual ground.
Modelling a Trajectory using Viewshed Techniques
Upon initial examination, it was considered that trajectories are parabolas.
Being such, they are easy to calculate using a parabola equation such as:
y = ax2 + bx + c
Unfortunately, this is only true for projectiles moving in a vacuum. In reality, a
bullet fired from a gun in the open air loses momentum through the resistance of
the air as it passes through. This produces a curve that starts gently upwards, but
at great speed, and gradually gets steeper as the wind resistance increases. From
the apex of the curve, when the forces of gravity outweigh the upward thrust of
the bullet, to its impact, the curve becomes dramatically steeper in a downward
direction. In a parabola, the upward and downward curves mirror each other.
Consequentially, experiments with parabolas were ended and details of true
trajectories of weapons were sought. The trajectory of a projectile depends on
its weight, the force with which it is launched and the amount of wind resistance
it offers. Trajectory data from various contemporary weapon range tables was
sourced and used in the preparation of firesheds of indirect fire weapons, under
the assumption that there is no wind at the time of firing.
The first stage in modelling the trajectory of a bullet using viewshed techniques
is to restrict the elevation of the viewshed to a one-degree aperture, representing
the line of sight of the gun. As the distance the projectile will travel varies
considerably with the angle of the gun (see Figure 51 – the initial angle of the
trajectory is equivalent to the angle of the gun), it is not suitable to calculate
curved trajectories using the entire vertical field of view from the pillbox
embrasure, as was possible for the flat trajectory and direct-fire weapons in the
previous section.
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Figure 50: Comparison between parabola and trajectory
Height of trajectory (in feet) above line of sight
at given distance from weapon in yards Range from weapon to
target in yards 0000
0
0000 200
0000 300
0000 400
0000 500
0000 600
0000 700
0000 800
0000 900
0000 1000
0000 1100
0000 1200
300 0 0.7 0 400 0 1.6 1.4 0 500 0 2.6 2.9 2 0 600 0 3.7 4.4 4.1 2.6 0 700 0 4.9 6.2 6.6 5.8 3.6 0 800 0 6.3 8.3 9.4 9.4 7.9 4.8 0 900 0 7.9 10.7 12.6 13.3 12.6 10.3 6.2 0
1000 0 9.7 13.4 16.2 17.8 18.0 16.5 13.2 7.8 0 1100 0 11.7 16.5 20.3 22.9 24.1 23.7 21.3 17.3 10.5 0 1200 0 14.0 19.9 24.8 28.5 30.9 31.7 30.7 27.5 21.9 12.5 0
Table 6: Trajectory Table for Rifle No 1 Mk 3 SMLE firing SAA .303 MkVII ammunition, with muzzle velocity of 2440ft/sec (War Office 1942d)
Note: As the Bren LMG uses the same ammunition as the SMLE, discussed above, its trajectory
is the same. Therefore, the data in Table 6 above is applicable to both weapons. The Bren LMG
manual (War Office 1942c) instructs users to view Vickers Machine Gun range tables, as these
are equivalent. Moreover all three weapons have a similar barrel length. It was assumed,
therefore, that short-range Vickers MMG trajectories are similar to those of the SMLE. This is a
roundabout way of obtaining Vickers range data, but was the only option open as no sources
were able to supply range tables for the obsolete Vickers MMG.
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SMLE Rifle Trajectory 1942
0
5
10
15
20
25
30
35
0 200 400 600 800 1000 1200
Range (yards)
Hei
ght o
f tra
ject
ory
abov
e lin
e of
sig
ht (f
eet)
Figure 51: SMLE trajectory plot
In order to maximise the dangerous space contained within the height of person,
it was standard procedure to sight the LMG so that its bullets would hit the
ground at 600yds (549m). At this range, the entire height of the trajectory is
within what was considered the average height of a soldier (War Office 1942c).
It must be noted that the range table above is calculated with the gun mounted at
ground level – i.e. zero feet. In use, the gun would, if mounted outside the
pillbox, be supported at a level of six inches to one foot (15-30cm) and when
used inside a pillbox, the gun would be mounted at approximately 1.45m from
the floor of the building (taken as ground level for this study, although some
pillboxes were dug in to hillsides to aid in camouflage). The concept behind
this ranging is that, on flat ground, attackers coming into contact with the
trajectory of a bullet ranged at 600yds would have been hit somewhere on their
body. The closer to the gun they stood, they would be hit in the foot or leg. The
further away they stood, the bullets would hit higher up their body. At the apex
of the trajectory, they would be hit in the head. On the descent of the bullet, they
would be hit from above, gradually lower down their bodies as they increased
their distance from the gun.
As the weapon can still traverse horizontally when its angle is set vertically,
there was no need to restrict the AZIMUTH1 and AZIMUTH2 values more than
the embrasure of the gun emplacement constrained them already.
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A simple viewshed such as this will not allow for the curvature of a projectile in
motion. Viewsheds are based on sight, and sight occurs in straight lines, which
cannot be manipulated easily. It was considered a more feasible task to alter the
heights of the ground surface to reflect the curvature of the straightened
trajectory. The concept is based on an analogy of the trajectory and ground
surface as being a single piece of rubber, the bottom face of which represents
the landform and the top face of which is curved upwards and then downwards,
representing the path of the trajectory. The process outlined above is simply
demonstrated by pushing down on the top of the rubber until the curved surface
is perfectly flat. Consequentially, the bottom surface will have been pushed
down by the amount needed to flatten the top and will represent the shape of the
trajectory, although inverted. A viewshed carried out on this deformed ground
was therefore considered to be an accurate fireshed for the chosen weapon.
The Simple Model, as created in ArcGIS
The Spatial Analyst distance calculator was used to create a circular raster
centred on a point shapefile representing the pillbox. The radius of this circle
was set to the range being investigated, and the procedure calculated the
distance from the pillbox to each pixel in the raster.
The values in the circular raster were then reclassified using Spatial Analyst into
the distance bands found on the SMLE range table. Each band was allocated the
value of the height of the trajectory at that point. This resulted in a raster made
up of concentric circles, with from the centre out, values that rose gradually then
fell. In effect, this was a circular trajectory around the pillbox point.
The raster calculator component of ArcGIS was then used to subtract the pixel
values of the circular trajectory from those of the elevation model at that point.
Its output, a temporary file, showed the terrain dipping down before returning to
its original level, in a complete circle.
A viewshed was then calculated from the pillbox point. The resulting image
represented the fireshed of the pillbox for the chosen weapon. The viewshed can
be calculated with the standard OFFSETB values explained in previous sections
to gauge the effect of pillboxes against different height targets.
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Figure 52: Original elevation model
Figure 53: Distance raster reclassified into 200yd intervals
Figure 54: Previous raster reclassified with trajectory height above line of sight
Figure 55: Result of subtracting Figure 54 from Figure 52
Figure 56: Viewshed calculated using
Figure 55 as DEM Figure 57: Resulting fireshed, displayed on
original elevation model
Problems with The Simple Model
The simple model produced a fireshed that is inaccurate on two accounts: The
trajectory created was stepped, not smooth, as the path of a bullet flying through
the air should be. This is due to the low resolution of the source data, and was
easily remedied.
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Interim values – x(interim) – were interpolated from the values either side
(upper x and lower x), where the size of interval (gap size) is known, as follows:
gapxinterimxinterimxsizegap
xlowerxuppergapx
+−=
−−=
)1()(
1
(The same formula applies to y values)
The other problem was apparent when the model was implemented on sites with
a difference in height between gun and target. A pair of MMGs at the northern
end of the study area were situated atop a bank, overlooking surrounding
countryside. Those on edge of the Crimson Hill plateau also look out over a
hillside that drops away suddenly. Firesheds from these guns showed no points
of contact at all. Had this been the case, guns at these points would be useless
against anything but falling parachutists. The reason for this error is the
assumption that the line of sight was horizontal, and therefore the trajectory
ended in mid air. Vickers MMGs, however, could tilt up and down to combat
such problems and would range on whatever ground was 600yds away (Hunt
2003). As can be seen from Figure 60 below, the line of sight of the elevated
gunner is angled down towards the target, and the trajectory displayed reflects
this. There is still a lot of dead ground beneath the trajectory of this gun in
which an enemy could move unscathed, although not as much as is present in
the model. A further problem can be visualised in which the target is higher than
the gun. In this instance, a horizontal fireshed would see bullets hitting the
ground below the target, when in reality, the gunner would aim the gun upwards
to counteract this.
Nevertheless, this technique offers the possibility of assessing whether
positioning the gun on the top of an embankment (or on high ground), giving
good fields of view but limited dangerous zones, would be better than
positioning the gun at the foot of the embankment (at ground level) with
reduced fields of view and shorter, but more effective fields of fire.
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Figure 58: ‘Footprints’ of trajectories
It is not enough to subtract a value from the height of the bullet corresponding
to the elevation of the line of sight. The range is measured along the line of sight
rather than the horizontal plane, but the values subtracted from the elevation
model are based on the horizontal ‘footprint’ of the line. At 90° from vertical,
the line of sight and horizontal footprint are equal. At higher or lower angles of
sight, the line of sight does not change length, but its horizontal footprint
becomes shorter. Due to this fact, it was necessary to rotate the trajectory curve
by the same angle as the line of sight.
Figure 59: Right angled triangles reflecting points on a trajectory
In order to obtain the angle of sight, basic trigonometry was used. A plane was
drawn at the target ground level, parallel with the horizontal line of sight. A
vertical line was drawn from this plane to the gun. Upon adding the angled line
of sight, a right-angled triangle is produced. Using sine rule and the knowledge
that when a straight line cuts a pair of parallel lines, the angles between the lines
are the same at opposite ends, the angle of sight was calculated (see below).
Inverted, this system also applies when the target height is above that of the
gun.
83
1
sin−
=
hypotenuseoppositea
Figure 60: Calculating the angle of sight
In order to rotate the trajectory, the straight-line distance was calculated
between each point and the gun, using Pythagoras’ theorem (a2 + b2 = c2), where
c is the point-gun distance, a is the range to the point and b is the height of the
point above the line of sight. The data was then rotated using a standard polar
transformation formula, using Microsoft Excel. Equations for the transformation
are as follows:
( )
−
++=
−− 1122 tansin90sin
xy
hgyxxnew
( )
−
++=
−− 1122 tansin90cos
xy
hgyxynew
Where: g = gun height h = hypotenuse length x = x-axis value y = y-axis value The Advanced Model
In order to calculate a fireshed using the resulting trajectory, it is necessary to
adjust the vertical angle constraints (VERT1 and VERT2) in order that they
reflect the angle of sight. VERT1 is set to the angle of sight, whilst VERT2 is
set to the angle of sight –0.1. The value for VERT2 is fairly arbitrary and can be
adjusted depending on the permutations of the GIS package in use, but should
always be an interval of one degree or less. This is to represent axis of the barrel
of the gun fixed at a certain elevation (and therefore range). Following this
procedure, the fireshed is calculated using the new trajectory data to the same
method as described in ‘The Simple Model’, above.
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As this method involves a great many manual processes, making calculation of
the firesheds of several guns a time-consuming and repetitive process, a Visual
Basic script to automate the process was coded by Graeme Earl, University of
Southampton. This script is included in Appendix V, but can be summarised as
follows:
A ‘personal geodatabase’ (alternative form of vector data storage to shapefiles)
is required containing point data for guns, coded with OFFSETA and B,
AZIMUTH1 and 2, VERT1 and 2, reflecting the desired output fireshed. Also
essential is an elevation model.
The user edits the script, adding file location data for the geodatabase, the
elevation model and a working folder. The (unmodified) trajectory data for the
desired range is added, in either imperial units or metric (a flag is set to instigate
a conversion procedure should it be required), together with the number of new
points to interpolate between each existing point, and finally the angle of sight
is input. On running the procedure, a raster image of a fireshed is produced for
each point in the geodatabase, based upon the constraints entered. In order to
overcome the need to know the angle of sight, a routine was added to allow
repetitions of the script with varying angles of sight – the trajectory being
rotated separately for each iteration of the algorithm. Each fireshed is calculated
on a separate record in the geodatabase, so in order for this to function correctly,
the source file requires consecutively numbered records located on the same
pillbox, with corresponding VERT1 and VERT2 values to the angles of sight
examined by the routine at the time.
This script is a great labour-saving device, well suited to the application of
calculating firesheds for an entire stopline. It is at present, however, limited by
being unable to recalculate VERT1 and VERT2 values automatically, making
large amounts of data redundancy necessary for the production of firesheds for
multiple ranges at one point. This is a trivial point that can be easily overcome
in the future.
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Figure 61: Complex Fireshed of MV1, Crimson Hill
A trial of the automated method on Vickers emplacement MV1, situated at the
edge of the Crimson Hill plateau, can be seen in Figure 61 above. This was
calculated to cover the majority of the vertical limits of the embrasure of a
Vickers box, namely 13° either side of the horizontal, to assess the suitability of
the model for estimating the angle of sight when it is unknown. The total angle
(26°) was divided into eighths, (3.375° each) in order to give overall cover.
The resulting fireshed consisted entirely of dead ground at all elevations but
13°, 9.625° and 6.25°, of which the latter produced the best results. This
suggests that the angle of sight of MV1 would need to be set at approximately
6.25° in order to be effective at 600yds. (NB. The band of dead ground in the
fireshed is caused by the 3.375° gap between calculations and can be reduced by
using smaller intervals).
The small amount of dangerous space highlighted by the fireshed indicates that
this gun was probably used as a long-range weapon, and the location of its
fireshed points towards its role as firing enfilade (i.e. providing a ‘fence of fire’
across the Stopline – see Figure 62, below).
This fireshed does indicate a problem with the Advanced Model. The model
ends at the point at which the trajectory from the range table grounds, i.e.
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crosses the line of sight. If the gun is being fired horizontally from the top of a
high embankment over lower ground, the bullet would not come into contact
with anything at the end of its trajectory and continue to curve downwards until
it hits the ground some metres beyond. This curve is not recorded in trajectory
tables, but is still an important factor in determining firesheds of high-mounted
weapons.
Despite the fact that these methods are in their infancy, it is most definitely
apparent that it is possible to create credible firesheds using GIS-based
technology that can be used to make assumptions as to the role of pillboxes and
gun emplacements in the study area – a factor applicable to countless other
types of indirect-fired projectile throughout time. Given more development, the
system will become more user-friendly and accurate, making it invaluable to the
military archaeologist and historian.
Figure 62: Theoretical and actual viewsheds, MV1, top of Crimson Hill, suggesting an
enfilade role (green = theoretical arc, red = viewshed)
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Chapter 3: Discussion of Results This study has opened many new avenues of research to the military
archaeologist. The use of GIS analysis in the archaeology of recent conflict has
a great number of positive points, and this work was unable to do more than
scratch the surface of what could become an incredibly useful and powerful
‘toolkit’ for the researcher.
Credibility of Results In order to assess the credibility of the results, it would be necessary to test them
against real data. As there was no invasion of England and no hostile action in
the southwest of the country, these defences were never tested. For obvious
reasons, it is not possible to re-equip the pillboxes and gun emplacements with
working weaponry and live ammunition, and attack for real using preserved
military vehicles. It is difficult, therefore, to determine the level of accuracy of
the firesheds and viewsheds to the 1940 situation, due to the lack of
contemporary data (particularly elevation data).
David Hunt, retired colonel and military researcher, who has assisted
throughout this study, spent his childhood in the area in the 1940s and 1950s,
and has visited the area regularly since), was invited to review the products. He
queried immediately some early viewsheds leading to revisions of the
vegetation in some areas. He found the revised viewsheds accurately portrayed
the intervisibility and carried out some limited on site checks on the ground in
the area. He then reviewed the later versions for the realism over the assessment
of the terrain by viewshed. All these he found to be most satisfactory within the
limits of summer vegetation in 2003. He then considered whether the firesheds
were reasonable for the weapons concerned, sited in the actual pillboxes and
emplacements. Having visited many of these over the last two years, he was
well satisfied that the firesheds were reasonable. Overall, he was impressed
with the power of the analyses and enthusiastic to become involved in
developing the techniques further and to assess other sections of the Taunton
Stopline.
This sort of outside involvement of an expert, with both local terrain
knowledge, military expertise, together with historical information from
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research was most useful in ensuring that the results were realistic and gave
confidence that the techniques could be effectively used on sites where such
knowledge is not available.
An overall assumption can be made that the level to which fireshed techniques
as a whole are realistic depends mainly on the quality and temporality of the
elevation model being used. Errors in elevation models, however small, can
significantly affect viewsheds (and therefore firesheds) produced, as explained
by Fisher (1991). Also vital are accurate locations and bearings for weapons,
and in the case of indirect fire weapons, accurate trajectory data, whether
documented or gained experimentally. If applying the method to a more ancient
example, for instance, a medieval trebuchet, it would be impossible to gauge
how accurate the resultant model was, and despite the comparative recentness,
the same is still true for the Second World War.
These analyses indicate some of the strengths and weakness of the Taunton
Stopline fortifications. It must not be forgotten that the planned garrison was
considerably stretched and while a single infantry battalion would have been
responsible for most of the sector from south of Durston to north of Wrantage,
the tactical doctrine of the time was the a battalion position would normally be a
square of 1000 yards (Hunt 2003). The communications of the battalion would
therefore have been severely stretched and much would have depended on the
determination of relatively junior officers and their soldiers to fight to the bitter
end. Equally, experiences in Belgium in May 1940 show how massive modern
fortresses like Eben Emal or Battice, which were considered at the time to be
impregnable, rapidly fell under German attack (Bierganz and Heeren 1990). In
the end, much depends on the skill, determination and bravery of the individual
soldier; together with some luck.
Lastly, when analysing the effectiveness of British anti-invasion defences, the
rapidity of their location, design and construction is a major factor. In 1949,
Winston Churchill wrote: ‘Nothing moves an Englishman so much as the threat
of an invasion, the reality unknown for a thousand years’. This provocation
should not be forgotten. It was a consequence of this threat that although the
reconnaissance for the Taunton Stopline was only made in late June 1940 but by
early August, most of the obstacles were well under way to completion and that
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by late October 1940 over 300 pillboxes and gun emplacements had been
constructed (Hunt Unpublished-a).
General Conclusions – what the system as it stands is capable of Providing good terrain data for a contemporary period is available, GIS-based
terrain analysis can be used in many ways by the military historian and
archaeologist:
• Reverse engineering methods can be used to find the most likely site for
features like observation posts, where their exact location is unknown,
but their role or requirements are known.
• Reverse engineering can also be used to estimate the most likely
orientation of pillboxes or gun emplacements, where this is not known
due to the demolition of the original structure.
• The primary roles of pillboxes and gun emplacements can be established
by examining their view and firesheds.
• Areas covered heavily with both vision and fire can be pinpointed,
leading to new questions of the reasoning behind this heavy cover (i.e.
what is in need of such a high level of protection).
• Likewise, areas with low cover can be examined and questioned as to
what was considered less important, or less of a risk, to the extent that it
was not defended as well.
• Vulnerable points of defended areas may be identified by the presence of
dead ground in close proximity to the front, and by ‘corridors’ of dead
ground enabling an attacker to get close without detection.
• The potential of field artillery can be evaluated through analysis of the
location and views from its observation points.
• The effect of trees and buildings on visibility and fields-of-fire is
immense and should at no point be underestimated. Likewise, the effect
(and indeed, presence) of standing crop is one that is highly unlikely to
be predictable easily.
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• Weak points in defended areas may not necessarily have been weakly
fortified, but may be easier to attack due to terrain, vegetation and
buildings providing covered approaches to up to the defences
themselves.
• Similarly, the relative strength of fortifications can be assessed. It may
be the case where two pillboxes cover more ground than their
neighbouring pillboxes, as the ground they cover is relatively flat and /
or devoid of obstructions.
• Defences can be evaluated against the appropriate military doctrine and
tactics of the period and the level to which they comply can often readily
be assessed.
• A military historian can tell much more about a defended area given this
new data. Viewsheds can tell whether defending forces would have had
advanced warning of an attack or whether they were likely to be
subjected to a nasty surprise. They can also show if the attackers would
have a good chance to view the defences and fire at them from a
distance.
Improvements / Future Directions All analysis in the study area is subject to ‘edge effects’ – the distribution of
pillboxes goes beyond the limitations imposed by the study area. Due to this
factor, towards the edges, the viewsheds and firesheds are not as accurate as
those in the middle of the area, as the fields of view and fire of any pillboxes
outside the area, but still able to see it, are not taken into consideration. This
should not be ignored by future users of these techniques as the results produced
from a cropped area can be misleading. Ways around this problem include
careful selection of a study area – ensuring all points for which view and fire is
to be calculated are included, and using a larger DEM and observer point
dataset when calculating cumulative viewsheds, which can then be cropped to
fit the rest of the data (Wheatley and Gillings 2002:209)
Accuracy of the elevation model, and of vegetation and buildings placed
thereon, is a major cause for concern. For example, Hunt has commented that
through personal memory, the trees around the study area were probably not as
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high as the 30m height assigned to them. Moreover, the differences in visibility
between trees in leaf in summer and trees without leaves in Winter can make an
enormous difference to a viewshed. The quality and accuracy, therefore, of the
digital elevation model is the most influential factor. Variation in elevations,
especially those closer to the observer, can have a massive (and unrealistic)
effect on fields of view and fire (Wheatley and Gillings 2002:209-10). As cited
previously, Fisher comments heavily on the effect of a bad DEM on viewsheds.
His solution to the matter is to use ‘fuzzy’ viewsheds – an element of noise is
added to the DEM before calculation of a viewshed. This noise is then changed
and a second viewshed created. When this process has been repeated several
times, the resulting binary viewsheds are added together. Pixels from the
resulting raster with higher values are more likely to be visible to the observer
point, and conversely, those with lower values are not (Fisher, P 1992).
Application of this system to fireshed calculation (thus creating ‘fuzzy
firesheds’ would aid in making more accurate assumptions of the probability of
being hit by fire in a certain location, rather than a possibly quite inaccurate yes-
or-no situation.
A more accurate contemporary elevation model could be obtained using
photogrammetry of stereo pairs of 1946 air photographs. This would, of course,
be subject to the same errors in accuracy mentioned elsewhere, but would aid in
the accurate study of an area. Although largely unaltered, the present study area
is cut briefly in the northwest corner by the M4 motorway, where the ‘shadow’
beyond the motorway embankment is clearly visible on the elevation model
(Figure 6), and by urban growth in areas such as Lillesdon. A contemporary
DEM would, obviously, exclude these factors, and could easily be made to
show actual heights of woodland, hedgerows and buildings without additional
(and error-prone) digitising.
It is almost impossible to predict such variables as restrictions to view imposed
by crops. For example, in the summer, a standing crop of wheat or barley would
be able to hide a man crawling through it. A crop of sweetcorn / maize may
even hide a light tank under certain conditions. In the autumn, however, fields
were generally ploughed and visibility to ground level would have been
possible. This is impossible to model accurately without detailed contemporary
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agricultural records that it is doubtful were kept at the time. In any case, it
would be necessary to decide a date and to estimate the height that the crop
might have grown to on that date.
When carrying out fireshed calculations with differing gun and target heights
(OFFSETA and OFFSETB values), calculations stop at the defined maximum
range examined. Bullets however do not stop here. It is improbable that a
weapon would be sited at the centre of a soup-bowl shaped patch of land,
although this is the assumption of the Advanced Method of calculating complex
firesheds above. It is a fair assumption to say that terrain would be uneven;
containing many ‘lumps and bumps’. If the gun is ranged on one of these, there
will be an overspill of fire when not pointing directly at it. The systems
developed above leave no room for the estimation of the point at which the
gunner or fire commander decided to set the sights on.
Future use of the system should take into account the actual elevations of
loopholes in pillboxes. A large proportion of pillboxes were dug in to the
surrounding ground to camouflage them to a greater extent, and to give more
protection against incoming fire. Others were sited high on embankments and
the effects of the additional elevation on the dangerous space significantly
reduced the effects of the weapon when engaging targets. In the above
calculations, loophole height was added on to the ground level based upon
standard plans. A better model would be obtained if individual spot heights
were taken using GPS or total station, or to a lesser degree of accuracy, tape
measure or rule.
Figure 63: Pillbox M1b, Wrantage, half excavated, illustrating the level to which it was buried to enhance its camouflage
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Figure 64: Pillbox M1a, Wrantage, obscured by trees, indicating its height above the
surrounding ground
(Note anti-tank blocks in foreground. See also Figure X – MAT601, also situated at a great
height)
Fireshed techniques need to be tested by applying to a more varied selection of
weaponry – heavy and light guns, anti-aircraft guns and mortars being examples
from the Second World War, although the study of weapons from different time
periods would also benefit from this kind of analysis.
In relation to machine gun fire, future versions of the complex fireshed
procedure should be able to estimate the size of a beaten zone, and studies
should be carried out on the use of vertical restrictions (VERT1 and VERT2) to
represent the cone of fire of a machine gun.
Earl’s script, developed to automate the construction of firesheds, has room for
development in user-friendliness and interactivity with source data. At present it
cannot alter VERT values in the weapon geodatabase, forcing the user to create
multiple entries with varying values. This is not a complicated problem. The
next step for this script is the creation of a graphical user interface (GUI) and its
development as an extension to ArcGIS that can be freely downloaded by
archaeologists and historians who already have suitable source data, in order
that they can calculate their own firesheds to add insight to their research.
In indirect fire, where for example an artillery gun is engaging a target from
behind a ridge, crest clearance is critical. It may be possible to predict the areas
where crest clearance exists enabling a artillery gun to engage targets there from
a specified gun position.
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Whilst not experimented with above, it is possible to model various scenarios to
see what effect the capture or destruction of one or more pillboxes would have
had on the viewsheds and fire sheds. This would give some indication of the
resilience of the defences. Were there to be ‘defences in depth’ with pillboxes
behind those guarding the obstacle, it would be possible to see how effectively
these might have filled the gap with fire from the rear.
Quality of View is a technique in need of development. At present, it means
little in terms of analysable data. It is foreseeable that estimations can be made
as to the best view of a target, where views from multiple points overlap.
Likewise, techniques developed by Fisher for analysis of ‘horizon viewsheds’
(coding viewsheds into four categories – 1 = visible, 2 = on local horizon, 3 =
on global horizon, 0 = invisible – 1996) is an area for further pursuit in the field
of military archaeology. In his 1996 paper, Fisher mentions how in the planning
and design of buildings, locating them off of the horizon makes them easier to
blend in with the existing infrastructure. This is also incredibly relevant to this
study in that pillboxes and other defence structures would be badly placed if
their outline was visible on the horizon (‘skylined’) by attacking troops. The
Vickers MMG emplacements on Crimson Hill are well dug into the hillside and
are prime examples of how this form of camouflage and protection was carried
out. The analysis of other sites in this way would give an insight into the
thought process that went into choosing their location.
It is strongly recommended that this work is carried further and developed more.
It would be a huge, informative addition to the English Heritage Defence
Landscapes Study (mentioned in the introductory chapter), which would assist
greatly in the understanding and interpretation of these monuments of twentieth
century warfare, and in heightening the awareness of the general public of
military sites that are commonly disregarded as uninteresting at present. The
Defence Landscape sites, which have already been selected on the Taunton
Stopline in Somerset, would be an obvious first choice as the terrain data should
be available from Somerset County Council and the knowledge of how best to
use it now exists. Moreover, there is a large and increasing amount of
information and analysis available concerning the Taunton Line defence plans,
the weapons and troops who would have manned the line from Hunt’s ongoing
95
work. Moreover, the Taunton Line would be a particularly worthwhile
example, as it is considered to be one of the best preserved stop lines in the UK
(Alexander 1998). These techniques could also be applied to modern military
planning but this needs further detailed investigation.
Conclusions The relative ease in calculating firesheds and analysing defence structures, using
standard procedures built in to most modern GIS, means that any researcher can
use an off-the-shelf package to create a more in-depth picture of the
effectiveness of defence sites from any time period. The applicability of the
methodology to any projectile in motion, whether launched by an Iron Age
person or by a twentieth century soldier, makes this an invaluable tool for all
branches of archaeology. With some development, it will become easier to use
and its output will be able to show far more than is possible using the current
system.
Figure 65: Overgrown and forgotten: A pillbox on the Great Western Railway, south of Creech, originally disguised as a signal box (David Hunt)
Currently, local and national government archaeologists are beginning to realise
the importance of Second World War military sites. Although there is a growing
public interest, recent military sites are still at risk of destruction through the
more widely held public disinterest. Application of fireshed analysis by local
and national authorities will bring a great deal more to the field in way of
removing public ignorance and provoking thought, memories and intrigue.
Enabling the public to see the sites as dynamic places which played a vital role
in the protection of the country, rather than static concrete structures, overgrown
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and forgotten relics of the past, will help to preserve the memory and ignite new
interest into the archaeology of one of the tensest periods of British, and indeed
world, history. In this age when the oral testimonies of those with first hand
experience of the Second World War are beginning to disappear, it is imperative
that the remaining archaeology is not lost in the same way, and by stimulating
public interest by bringing sites alive, we can be sure this will never happen.
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Appendix I: Background to the Taunton Stopline The Taunton Stopline runs for approximately 50 miles from the mouth of River
Brue at ST300470 to the mouth of the River Axe in Devon at SY898256 (with
some infrastructure in Dorset). Some rear positions were prepared to the east of
line. It connected to the ‘GHQ Line Green’ running east along River Brue
(Somerset County Council, PRN 15450).
The line followed the River Parrett to Bridgwater where it joined the Bridgwater
to Taunton Canal (Somerset County Council, PRN 43826) at ST304362. From
Creech St Michael at ST271256 if followed the old Chard Canal (Somerset
County Council, PRN 53321) until at ST340160, southwest of Ilton it joined the
Great Western Railway (Somerset County Council, PRN 55451). The line left
the railway to the north of Chard Junction (Somerset County Council, PRN
55435) at ST338049 from where it followed the Southern Railway (Somerset
County Council, PRN 57006) and River Axe running south into Devon at
ST329028.
Figure 66: View from the top of Crimson Hill north towards Wrantage
Route of Chard Canal (also that of Stopline) marked (David Hunt)
98
The planned infrastructure (most of which was built) included 233 pillboxes, 61
medium machine gun emplacements, 21 anti-tank gun emplacements, 83 road
blocks, 22 railway blocks and 46 demolitions. The anti-tank obstacle consisted
of about 24 miles of waterways, 7 miles of improved water obstacles, 11 miles
of anti-tank ditches and 8 miles of artificial obstacles (e.g. cubes).
Figure 67: Type 24 pillbox, Buckland, Somerset (Tacchi 2003)
The Type 24, in the middle distance, really stands out as there is no cover on the east bank at this stage of the canal. It covered a crossing place where a swing
bridge had been demolished in July 1940 as a Preliminary Demolition. The main Paddington to Penzance railway line runs along just behind it.
[Map ref. ST 297271] (Tacchi 2003)
From autumn 1940, twelve locations were prepared for all-round defence as
‘anti-tank islands’ of which nine were in Somerset - Bridgwater (Somerset
County Council, PRN 16380), Durston (Somerset County Council, PRN
16340), Creech St Michael (Somerset County Council, (PRN 16381), Wrantage
and Crimson Hill (Somerset County Council, PRN 16382), Ilton (Somerset
County Council, PRN 16383), Ilminster (Somerset County Council, PRN
16384), Chard (Somerset County Council, PRN 16385), Forton and Perry Street
(Somerset County Council, PRN 16386) (Adapted from Hunt Unpublished-a).
Reconnaissance for the stopline took place between the 27th and 29th June 1940
and construction was completed by November of the same year (Hunt 2003). It
was constructed, like the other stoplines in Britain, of ‘a combination of natural
and man-made anti-tank obstacles’ (Alexander 1998:9). Rivers, canals and
railways were chosen as obstacles as their banks were often steep enough to
prevent a tank climbing them. In areas where the banks were not as steep as
desired, they were scarped and built up to a level at which they were effective,
or were supplemented with concrete posts such as those in Figure 69. In areas
without banks, for instance, where the stopline crossed fields, anti-tank ditches
were excavated and anti-tank blocks were laid. Roads were fitted with grooved
concrete blocks on either side into which sections of railway line were to be
inserted to block the road. Bridges were packed with explosives to be
demolished when appropriate and mines were placed in sockets in both roads
and bridges to immobilise tanks by blowing their tracks off. Much of this
defence architecture still exists and the
Taunton stopline has been credited as one
of the best-preserved lines in the country
(Alexander, cited by Hunt Unpublished-
a). Pillboxes and road blocks, due to their
design, are not easy to demolish, and as
such, remain, overlooked and overgrown
in fields and hedgerows. Demolition has
occurred where the defences presented a
hazard to traffic, and some landowners
w
ca
so
br
th
of
m
ad
5 TEn
Figure 68: Possible mine socket in a railway bridge, Donyatt, Somerset
(£1 coin shown for scale)
99
ere paid five or ten pounds to remove pillboxes, but kept the money without
rrying out the work (Hunt 2003). Smaller, less obvious features such as mine-
ckets and now bricked-up demolition charge compartments in the supports of
idges are clearly visible to the trained eye. It was discovered on a field trip to
e area as part of the research for this study, that even the more portable parts
stopline defences are still to be found, when a length of railway track
easuring the exact length of a road block was discovered in a hedgerow
jacent to a road block site at Hammonds Farm, west of Crimson Hill.5
he section of railway track was photographed and reported to Chris Webster, Historic vironment Record Officer, Somerset County Council.
100
Figure 69: Concrete anti-tank posts added to a railway embankment, Donyatt, Somerset
Figure 70: Road blocks either side of a canal bridge, Donyatt, Somerset
(Concrete blocks slotted to accept sections of railway track)
101
Figure 71: Section of the Taunton Stopline defence plan (Crimson Hill), 1940
(Wills Collection. NMR, Swindon)
For more information on the way war affected Somerset and the way in which the county was defended, see M. Hawkins’ book, ‘Somerset at War 1939 – 1945’.
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Appendix II: Site List SMR ID NGR Designation Description Type
44647 ST 282 258 (ST 22 NE) N68 Pillbox (N68) site, Cathill Farm, Creech St Michael Pillbox
55175 ST 3136 2217 (ST 32 SW) T36 Pillbox, NE of Crimson Hill Farm, Curry Mallet Pillbox
11982 ST 3043 2796 (ST 32 NW) N62 Pillbox (N62), NW of Cogload Farm, Durston Pillbox
15904 ST 3112 2786 (ST 32 NW) T20 Pillbox (T20), W of West Lyng Pillbox
15466 ST 3089 2781 (ST 32 NW) T22 Pillbox (T22), NE of Cogload Farm, Lyng Pillbox
15042 ST 3116 2778 (ST 32 NW) T21 Pillbox (T21), S of Durston Pillbox
44322 ST 3034 2774 (ST 32 NW) NV14
Vickers machine gun pillbox (NV14), NW of Cogload Farm, Durston Vickers
44323 ST 3036 2768 (ST 32 NW) NV15
Vickers machine gun pillbox (NV15), NW of Cogload Farm, Durston Vickers
44321 ST 3037 2764 (ST 32 NW) T23 Pillbox (T23), NW of Cogload Farm, Durston Pillbox
44304 ST 2969 2708 (ST 22 NE) N63 Pillbox (N63), S of Durston Pillbox
44319 ST 2924 2689 (ST 22 NE) N64 Pillbox (N64), NE of Charlton Pillbox
44302 ST 2910 2655 (ST 22 NE) N65 Pillbox (N65), Charlton Pillbox
44300 ST 2876 2612 (ST 22 NE) N66 Pillbox (N66), SW of Charlton Pillbox
44298 ST 2848 2590 (ST 22 NE) N67 Pillbox (N67), E of Cathill Farm, Creech St Michael Pillbox
44311 ST 2706 2559 (ST 22 NE) N72 Pillbox (N72) at canal junction, Creech St Michael Pillbox
44532 ST 2746 2555 (ST 22 N70 Pillbox (N70), Creech St Michael Pillbox
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NE)
44530 ST 2731 2546 (ST 22 NE) N71 Pillbox (N71), Creech St Michael Pillbox
44287 ST 2750 2545 (ST 22 NE) T30 Pillbox (T30), E of Creech St Michael Pillbox
44338 ST 2705 2541 (ST 22 NE) N73 Pillbox (N73), N of Mill Lodge, Creech St Michael Pillbox
44288 ST 2768 2530 (ST 22 NE) T31 Pillbox, E of Creech St Michael Pillbox
44282 ST 2706 2520 (ST 22 NE) N74 Pillbox, in canal bed, S of Creech St Michael Pillbox
15886 ST 2734 2520 (ST 22 NE) T33 Pillbox (T33), S of Creech St Michael Pillbox
44289 ST 2775 2518 (ST 22 NE) T32 Pillbox, E of Creech St Michael Pillbox
15981 ST 2787 2429 (ST 22 SE) N79 Pillbox (N79), N of Thornfalcon Pillbox
44297 ST 2814 2427 (ST 22 SE) N80 Pillbox, N of Thornfalcon Pillbox
44301 ST 2887 2418 (ST 22 SE) N82 Pillbox, E of Thornfalcon Pillbox
44299 ST 2846 2411 (ST 22 SE) N81
Pillbox and AT obstacle, E of Canal Farm, Thornfalcon Pillbox
44325 ST 2951 2355 (ST 22 SE) N83 Pill box, NW of Lillesdon Court, Lillesdon Pillbox
44306 ST 2978 2346 (ST 22 SE) NV16a Pillbox, NW of Lillesdon Court, Lillesdon Vickers
44320 ST 2979 2339 (ST 22 SE) NV16b Pillbox, NW of Lillesdon Court, Lillesdon Vickers
44303 ST 2971 2332 (ST 22 SE) N84a Pillbox, NW of Lillesdon Court, Lillesdon Pillbox
44305 ST 2985 2325 (ST 22 SE) NV17a Pillbox, W of Lillesdon Court, Lillesdon Vickers
15420 ST 2989 2322 (ST 22 SE) NV17b Pillbox, W of Lillesdon Court Vickers
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15419 ST 3018 2306 (ST 32 SW) N85 Pillbox site (N85), S of Lillesdon Pillbox
44326 ST 3042 2283 (ST 32 SW) NV18 Pillbox, N of Honey Farm, Wrantage Vickers
15928 ST 3104 2283 (ST 32 SW) T40 Pillbox site, Wrantage Pillbox
44327 ST 3044 2282 (ST 32 SW) NV19 Pillbox, N of Honey Farm, Wrantage Vickers
15883 ST 3083 2280 (ST 32 SW) T41 Pillbox site (T41), N of Weaver's Farm, Wrantage Pillbox
44328 ST 3050 2278 (ST 32 SW) N86 Pill box, N of Honey Farm, Wrantage Pillbox
15884 ST 3111 2270 (ST 32 SW) T39 Pillbox (T40), Wrantage Pillbox
44329 ST 3063 2268 (ST 32 SW) MAT601
Gun emplacement, N of Higher Wrantage Farm, Wrantage AT Gun
44330 ST 3076 2252 (ST 32 SW) M1a Pillbox, N of Higher Wrantage Farm, Wrantage Pillbox
44334 ST 3121 2247 (ST 32 SW) T38 Pillbox, S of Ludwells Farm, Wrantage Pillbox
44331 ST 3084 2241 (ST 32 SW) MAT602
Gun emplacement, E of Higher Wrantage Farm, Wrantage AT Gun
44332 ST 3087 2237 (ST 32 SW) M1b Pillbox, SE of Higher Wrantage Farm, Wrantage Pillbox
55181 ST 3138 2224 (ST 32 SW) T37 Pillbox, S of Ludwell's Farm, Curry Mallet Pillbox
44333 ST 3116 2194 (ST 32 SW) M61 Pillbox, N of Crimson Hill Farm, Wrantage Pillbox
44336 ST 3130 2194 (ST 32 SW) MV1 Pillbox, NE of Crimson Hill Farm, Wrantage Vickers
44335 ST 3128 2192 (ST 32 SW) MV1a Pillbox, NE of Crimson Hill Farm, Wrantage Vickers
55179 ST 3150 2170 (ST 32 SW) MAT603
Gun emplacement, SE of Crimson Hill Farm, Curry Mallet AT Gun
55176 ST 3155 2163 (ST 32 SW) M62 Pillbox, SE of Crimson Hill Farm, Curry Mallet Pillbox
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55259 ST 3164 2153 (ST 32 SW) MAT604 Gun emplacement, W of Curry Mallet AT Gun
55180 ST 3195 2129 (ST 32 SW) M2 Pillbox, SE of Crimson Hill Farm, Curry Mallet Pillbox
99991 ST 3135 2188 M1 Missing pillbox, Crimson Hill plateau Pillbox
99992 ST 2970 2425 N84 Missing pillbox, Solomon's Hollow, Lillesdon. Type 24, Shell-proof Pillbox
44317 ST 2716 2489 Pillbox, railway embankment, E of Ruishton Pillbox
44286 ST 2716 2497 T Pillbox, on canal embankment, E of Ruishton Pillbox
44283 ST 2715 2501 Pillbox in tunnel, Ruishton, Tunnel Pillbox
44324 ST 2731 2456 Pillbox, E of Ruishton Pillbox
44318 ST 2748 2445 Pillbox, SE of Ruishton Pillbox
44281 ST 2706 2510 Pillbox, on railway, E of Ruishton Pillbox
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Appendix III: Principles of Defence (Adapted from ‘Tactical Notes for Platoon Commanders’, War Office 1941)
A Post in Concrete: Fighting from a Pillbox
(1) The concrete pillbox is a great aid to defence if intelligently used; if not,
it may become a death-trap.
(2) Concrete is a protection against bullets, shell splinters, and weather.
Sometimes it affords protection against shell fire. If properly
camouflaged, it is also a protection from ground and air observation.
(3) Many concrete posts are not complete protection against a direct hit
from a shell or from an aerial bomb. They all have the disadvantage of
limiting the field of view and the field of fire. The garrison will be
unable to use all their rifles at one and the same time because of the
fewness of the loopholes. Finally, the garrison is hindered in the
employment of the hand grenade and bayonet;
(4) Therefore the garrison of a pill box locality will act as follows:
(a) The sentry or sentries on duty will be stationed, outside the
pillbox, where they can see and hear all round them.
(b) Temporary cover from view, shell fire, and aerial bombing
maybe sought inside the pillbox; but beware that the enemy are
not creeping towards you under this covering fire, whilst you are
biding inside.
(c) When the attack comes, the light machine gun or machine gun
will fire from the pillbox, if it can carry out its task. If not, it
must come out to a prepared position.
(d) Those men who cannot use their weapons inside must man-the
trenches outside-where they can do their duty.
(e) If the pillbox is surrounded all except for those who can fire
from the loopholes, will fight outside, where they can employ all
their weapons to the best advantage.
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Scenario: The Defence of a Bridge (Applicable to the Taunton Stopline, see
Figure 72)
(1) The garrison will be astride the bridge. Posts should embrace the
roadblocks and be sited to cover all immediate approaches to the bridge.
(2) The barbed wire obstacle must be sited so that every yard of it is under
direct observation and fire.
(3) The aim of the garrison must be that no unauthorized person can
penetrate in to the perimeter of the bridge defence, i.e. the wire round it.
(4) The garrison, therefore, is disposed to safeguard the bridge against an
enemy who:
(a) may attack from any direction;
(b) may approach within assaulting distance under cover of
darkness, early morning mist, artificial smoke, or by covered
approaches;
(c) or may attempt to overcome the garrison by a ruse, i.e., by
arriving in a motorcar, or on foot, dressed as civilians or as
British soldiers.
(5) The command post will have an observation post (O.P.) from which the
maximum amount of ground immediately surrounding the bridge can be
seen. At least one sentry will be on duty throughout the hours of
daylight.
(6) All defensive posts and positions will be concealed from ground and air
observation by camouflage. Alternative positions, i.e., other positions
from where the same task can be performed, will always be constructed.
(7) Wherever possible, visual communication will be established from the
garrison on the bridge to the nearest neighbouring unit.
(8) Every bridge garrison will have signal rockets as an alarm signal that
they are being attacked.
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(9) Every bridge garrison will include at least one bicycle and one or more
orderlies who will know the best way to the nearest neighbouring unit
which can give assistance if the garrison of the bridge is in difficulties.
(10) If the garrison is larger than that required for the close defence of
the bridge, a ring of outposts may be employed.
Figure 72: Defending a bridge or crossing point (Mace 1996:4)
Scenario: Holding a River or Canal (Applicable to the Taunton Stopline)
(1) The forward garrison will be so disposed that they can cover the water
by direct observation and fire: In no circumstances will any stretch of
water be left un-guarded. The enemy will certainly cross by any such
unguarded stretch.
(2) Every post sited to guard the water will be hidden and camouflaged
from ground observation and, as far as possible, air observation as well.
(3) Alternative sites will be prepared, that is, sites from which the same task
can be performed but in a different locality. The garrison, if spotted and
shelled, can then move to a safer place and avoid casualties.
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(4) Local reserves will be so placed that they can immediately counter-
attack any enemy who have succeeded in gaining a footing on our bank.
This is their duty.
(5) At night, or during mist or fog, moving patrols must guard the gaps
between posts to ensure that the water is kept under constant
observation,
(6) When time permits, dummy' trenches of conspicuous nature will be
made to draw the enemy's fire on to places where it will not harm our
troops.
The scenarios above are applicable to the Taunton Stopline with the following
main variation: each post mentioned would, instead of being a temporary
construction, have been formed by one or more pillboxes, thus making it harder
for an attacking enemy to destroy those defending the obstacle and consequently
cross it.
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Appendix IV: German Attack Tactics German techniques of attack relied mainly upon armoured fighting vehicles.
Light and medium tanks formed the hard core of a ‘Panzer’ or armoured
division. To prepare the way ahead of them, there were armoured cars and
motorcyclist machine gunners. For close support there were batteries of field
artillery and batteries of anti-tank guns and machine guns. To occupy the
ground that the tanks had overrun, trucks and troop carriers followed close
behind, deploying infantry troops to hold the newly captured ground. Engineers
were carried to advise on crossing water obstacles, and a crew of maintenance
personnel ensured mechanical equipment and vehicles did not break down.
Communication was key and radio operators and signallers ensured all parties
were able to pass on vital information. The division also had its own aircraft, in
constant communication with the front-line troops, to provide air support to the
attack. The armoured corps as a whole was the pride of the German army and
nothing was spared in providing it with a solution to every situation.
An attack began long before the first shell was fired. A great number of
divisions was assembled in an area invisible to the defending force, then a
‘crash bombardment’ of the defences ensued, with attack coming from the air
and from artillery weapons on the ground. The leading tanks quickly followed
this up with a vigorous mass advance in which obstacles were charged through,
brushed aside or overcome in some way. Tactics were ruthless to the level that a
leading tank would be sacrificed to fill a ditch so that others could drive over it
and continue unhindered. This kamikaze nature continued into minefields – if
they were destroyed, others would know that the ground they had already
crossed was safe, and clearing the way would be much easier. Used thus, with
reckless disregard of loss, at full speed and with maximum weight, the tanks
would certainly, at one point or several, succeed in bursting through the defence
network.
This ‘break in’ was only the first phase, after which the next aim was to cripple
or destroy the defending air force before it had the chance to give warning of the
coming assault. When aircraft could not be destroyed, prolonged attacks on
aerodromes would ensure aircraft were grounded and could not retaliate. The
air, therefore, was kept clear for the dive-bomber (vulnerable to fighter aircraft,
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so only deployed at this point) to clear up any centres of anti-tank resistance that
may have survived the initial wave of attack. Immediately following dive-
bomber attack, tanks and infantry would ‘mop up’ the survivors, enabling even
the most formidable of defences to be overcome.
Immediately the first tanks had breached the defended line, infantry and faster
vehicles (motorcycles and armoured cars) would pour through the gap leaving
the slow moving tanks to clear up localised resistance. This influx of troops was
designed to thrust boldly and unhesitatingly ahead in their appointed zones of
action. Some would fan out on either side of the gap and attack the unbroken
portions of the line from the rear – a situation seldom planned for. This would
widen the opening for more reinforcements to enter. Most, however, would
thrust deeper into the newly gained land, aiming for the administrative
organisations which were largely undefended, deprived of which an army can
never fight or hold together for long. Headquarters, communications, dumps,
depots, supply and transport columns, repair shops, railways, airfields and more
were the new targets, with the aim of causing confusion amongst the defending
force. Aircraft were also re-routed to this task. Panic, confusion and congestion
were the new tactics in the field.
(Adapted from Anon 1942:88-93)
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Appendix V: Visual Basic Complex Fireshed Script By Graeme Earl Attribute VB_Name = "Module1" Option Explicit Public SCRIPTroot As String Public DBFFiles As String Public TEMPFiles As String Public RASTERFiles As String Public MAINDEM As String Public IMPERIALDataInput As String Public MaxRANGEofFIRE As Long Public FEATUREField As String Public NUMBERofFEATURES As Integer Public BarrelDepression As Single Public NUMBERBarrelIterations As Integer Public MaxBarrelAngle As Single Public BarrelIterationValue As Single Sub SetGlobals() ' set constants SCRIPTroot = "y:\" DBFFiles = SCRIPTroot & "gis\" TEMPFiles = SCRIPTroot & "Temp\" RASTERFiles = SCRIPTroot & "gis\" MAINDEM = "dem25mtrees" IMPERIALDataInput = True MaxRANGEofFIRE = 600 ' in yards for the weapon FEATUREField = "CountMe" ' the name of the field in your geodatabase with feature ID integers from 1 upwards NUMBERofFEATURES = 1 ' the number of features in your table (NB this the number of guns not every row corresponding to a barrel angle) NUMBERBarrelIterations = 9 ' the number of angle samples to produce MaxBarrelAngle = 13 ' the maximum barrel angle, in ArcGIS "VERT" notation BarrelIterationValue = 3.375 ' degrees ' NB: the Maximum and calculated barrel angles must fall within the constraints for the pill box/ weapon ' Also the values in the weapon feature table must match the above ' e.g. with number barrel it as 5 and max angle as 45 and barrelitvalue as 10, five samples will be produced at 45, 35, 25, 15 and 5 degrees ' INSTRUCTIONS ' Ensure all of the above variables are completed an correct. For example, do the directories exist ? Is the number of features ' the same as the table in the geodatabase ? Ensure that only one feature geodatabase is loaded as the script searches down
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' until it finds one and uses the first one it finds. Also ensure that the Feature field matches that specified above and that ' this field contains ALL INTEGER values between 1 and your value for NUMBERofFEATURES. ' If necessary change the bounding box values for the calculations. These use the values a few lines below. ' Finally, go to the ReclassifyRaster function and make chanes to the reclassification parametres as required. End Sub Sub IDigGuns() 'set mouse cursor to hourglass Dim pMCur As IMouseCursor Set pMCur = New MouseCursor pMCur.SetCursor 2 ' declare variables Call SetGlobals Dim inputRasterFilename As String Dim RANGEofFIRE As Integer Dim XMin As Double Dim YMin As Double Dim XMax As Double Dim YMax As Double RANGEofFIRE = MaxRANGEofFIRE If IMPERIALDataInput = False Then RANGEofFIRE = Int(RANGEofFIRE * 0.9144) End If ' **************************** These values define the analysis bounding box ************** ' default values to enclose whole study area XMin = 325800 YMin = 120700 XMax = 332200 YMax = 128200 'XMin = 331280 - RANGEofFIRE 'YMin = 121920 - RANGEofFIRE 'XMax = 331280 + RANGEofFIRE 'YMax = 121920 + RANGEofFIRE ' **************************** These values define the analysis bounding box **************
114
'inputRasterFilename = "stline3" ' Loop through the table creating the rasters Dim CurrentBarrelIteration As Integer CurrentBarrelIteration = 0 Dim CurrentFeature As Integer For CurrentFeature = 1 To NUMBERofFEATURES * NUMBERBarrelIterations CurrentBarrelIteration = CurrentBarrelIteration + 1 ' Loop through the angles of barrel depression BarrelDepression = MaxBarrelAngle - ((CurrentBarrelIteration - 1) * BarrelIterationValue) ' angle of the gun Dim NewRangeRaster As IRaster Set NewRangeRaster = TheRangeRaster(RANGEofFIRE, XMin, YMin, XMax, YMax, CurrentFeature) ' open raster 'Dim OpenedRaster As IRasterDataset 'Set OpenedRaster = OpenRasterDataset(RASTERFiles, inputRasterFilename) ' perform reclassification Dim ReclassifiedRaster As IRaster Set ReclassifiedRaster = ReclassifyRaster(NewRangeRaster) ' Creates the float version and divides by 100 to create centimetres Dim FloatedRaster As IRaster Set FloatedRaster = FloatDividedRaster(ReclassifiedRaster) Dim RasterWithNoNoData As IRaster 'Set RasterWithNoNoData = RemoveNoData(FloatedRaster) Set RasterWithNoNoData = FloatedRaster Dim CutDEMRaster As IRaster Set CutDEMRaster = SubtractCone(RasterWithNoNoData) Dim VisibilityRaster As IRaster Set VisibilityRaster = GetVisibility(CutDEMRaster, CurrentFeature) ' Add raster to display - use the next 5 lines to display stages in construction 'Call AddRasterLayer(NewRangeRaster) 'Call AddRasterLayer(ReclassifiedRaster) 'Call AddRasterLayer(FloatedRaster) 'Call AddRasterLayer(RasterWithNoNoData) 'Call AddRasterLayer(CutDEMRaster) ' Add fireshed raster to display Call AddRasterLayer(VisibilityRaster)
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' reset the barrel angle loop If CurrentBarrelIteration = NUMBERBarrelIterations Then CurrentBarrelIteration = 0 End If Next CurrentFeature Set pMCur = Nothing Dim MessageString MessageString = "Done creating firesheds. Created " & NUMBERofFEATURES If NUMBERofFEATURES = 1 Then MessageString = MessageString & " fireshed for each of " & NUMBERBarrelIterations & " barrel angles" Else MessageString = MessageString & " firesheds for each of " & NUMBERBarrelIterations & " barrel angles" End If MsgBox MessageString, vbOKOnly, "IDigGuns Completed" End Sub Function TheRangeRaster(RANGEofFIRE As Variant, XMin As Double, YMin As Double, XMax As Double, YMax As Double, CurrentFeature As Integer) As IRaster ' calculate new maximum range RANGEofFIRE = ConvertRange(MaxRANGEofFIRE, 0, BarrelDepression, True) 'On Error GoTo ERH: ' Get the Map Dim pMxDoc As IMxDocument Set pMxDoc = ThisDocument Dim pMap As IMap Set pMap = pMxDoc.FocusMap ' Get the input source data from the first layer in ArcMap Dim pGeoDs As IGeoDataset Dim pLy As ILayer Dim ThisLayer As Integer ' counter for looping through layers Dim NoFeatures As Boolean ' checks whether the feature has been found NoFeatures = False For ThisLayer = 1 To (pMap.LayerCount) Set pLy = pMap.Layer(ThisLayer - 1)
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' if the feature layer is found then use it If TypeOf pLy Is IFeatureLayer Then NoFeatures = False Exit For Else NoFeatures = True End If Next ThisLayer If NoFeatures = True Then MsgBox "The appropriate feature layer must be loaded." Exit Function End If Dim pFeatureLy As IFeatureLayer Set pFeatureLy = pLy Set pGeoDs = pFeatureLy.FeatureClass Dim CurrentID As Integer Dim CurrentField As String CurrentID = CurrentFeature CurrentField = FEATUREField Dim CurrentPoint As IFeatureClassDescriptor Dim sFieldName As String Dim pQueryFilter As IQueryFilter Set pQueryFilter = New QueryFilter ' Set the where clause pQueryFilter.WhereClause = CurrentField & " = " & CurrentID sFieldName = CurrentField Set CurrentPoint = New FeatureClassDescriptor CurrentPoint.Create pGeoDs, pQueryFilter, sFieldName ' Create a Distance operator Dim pDist As IDistanceOp Set pDist = New RasterDistanceOp ' Set output workspace Dim pEnv As IRasterAnalysisEnvironment Set pEnv = pDist Dim pWS As IWorkspace Dim pWSF As IWorkspaceFactory Set pWSF = New RasterWorkspaceFactory Set pWS = pWSF.OpenFromFile(TEMPFiles, 0) Set pEnv.OutWorkspace = pWS ' Set output extent and cell size Dim pExt As IEnvelope Set pExt = New Envelope pExt.XMin = XMin pExt.YMin = YMin pExt.XMax = XMax pExt.YMax = YMax
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pEnv.SetExtent esriRasterEnvValue, pExt Dim CellRes As Variant CellRes = 10 pEnv.SetCellSize esriRasterEnvValue, CellRes ' Perform the Euclidean distance Path Dim pRangeOutRaster As IRaster Set pRangeOutRaster = pDist.EucDistance(CurrentPoint, RANGEofFIRE) ' Add it into ArcMap ' Dim pRLayer1 As IRasterLayer ' Set pRLayer1 = New RasterLayer ' pRLayer1.CreateFromRaster pRangeOutRaster ' pMap.AddLayer pRLayer1 Set TheRangeRaster = pRangeOutRaster 'ERH: ' MsgBox "gone wrong: " & Err.Description ' Exit Sub End Function Function ReclassifyRaster(pInputDataset As IRaster) As IRaster 'On Error GoTo ERH ' Create the RasterReclassOp object Dim pReclassOp As IReclassOp Set pReclassOp = New RasterReclassOp ' Open a remap table using the OpenTableFromDBFFile function below 'Dim pRemapTable As ITable 'Set pRemapTable = OpenTableFromDBFFile(DBFFiles, "RemapTable2.dbf") Dim RasterToReclass As IRaster Set RasterToReclass = pInputDataset ' Set the Remap using the number remap method Dim pRemap As IRemap Dim pNRemap As INumberRemap Set pNRemap = New NumberRemap 'pNRemap.LoadNumbersFromTable pRemapTable, "Out", "From", "To", "Mapping" Dim Ranges(12) As Long ' range end points Dim Elevations(12) As Single ' heights at sample points on curve Dim DivisionsPerRange As Single ' number of divisions Dim Samples As Integer ' number of range samples
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Dim ImperialInput As Boolean ' whether input data is in imperial (default) Dim OutputElevation As Integer ' the output elevation Ranges(0) = 0 Elevations(0) = 0 ' *********** complete the ranges and elevations arrays ******* Ranges(1) = 100 Ranges(2) = 200 Ranges(3) = 300 Ranges(4) = 400 Ranges(5) = 500 Ranges(6) = 600 Elevations(1) = 1.85 Elevations(2) = 3.7 Elevations(3) = 4.4 Elevations(4) = 4.1 Elevations(5) = 2.6 Elevations(6) = 0 ' Enter the number of samples. Do NOT include the first zero value but do include the final zero value ' The final zero value should also be entered in the two arrays e.g. Ranges(11)= 1100 Elevations(11) = 0 ' If you have less than the above arrays you can ignore the array slots after the SAMPLES value ' The number of samples INCLUDES the first and last zeros Samples = 6 DivisionsPerRange = 5 ' Convert ranges and elevations to cope with rotated trajectory. In the words of MC Hammer - can't touch this Dim LoopThroughArray As Integer For LoopThroughArray = 1 To Samples - 1 Ranges(LoopThroughArray) = ConvertRange(Ranges(LoopThroughArray), Elevations(LoopThroughArray), BarrelDepression, True) Elevations(LoopThroughArray) = ConvertRange(Ranges(LoopThroughArray), Elevations(LoopThroughArray), BarrelDepression, False) Next ImperialInput = IMPERIALDataInput ' *********** complete the ranges and elevations arrays *******
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' *************** Do not change anything below here *********** Dim RangeLength As Integer Dim ThisDivisionDifference As Single Dim ThisElevationDifference As Single Dim NumberOfSamples As Integer Dim NumberOfDivisions As Integer Dim LastButOneDivision As Integer Dim CurrentRangeValue As Single Dim CurrentElevationValue As Single Dim CurrentElevation As Single Dim PreviousRange As Single PreviousRange = 0 Dim OutputString As String ' Loop through the ranges calculating the inter-range difference, stopping at the penultimate sample For NumberOfSamples = 0 To (Samples - 2) RangeLength = Ranges(NumberOfSamples + 1) - Ranges(NumberOfSamples) ' Calculate the length difference of each successive new division ThisDivisionDifference = RangeLength / DivisionsPerRange ' Calculate the elevation difference for each of these divisions ThisElevationDifference = (Elevations(NumberOfSamples + 1) - Elevations(NumberOfSamples)) / DivisionsPerRange ' Finds the start of the last division and loops through this many times adding Values LastButOneDivision = Fix(DivisionsPerRange) For NumberOfDivisions = 1 To LastButOneDivision ' Multiply the position in the sequence by the difference per division If NumberOfDivisions = 1 Then ' Check for the first value CurrentRangeValue = 0 + Ranges(NumberOfSamples) Else CurrentRangeValue = ((NumberOfDivisions - 1) * (ThisDivisionDifference)) + Ranges(NumberOfSamples) End If If NumberOfDivisions = 1 Then ' Check for the first value CurrentElevationValue = 0 + Elevations(NumberOfSamples) Else CurrentElevationValue = ((NumberOfDivisions - 1) * (ThisElevationDifference)) + Elevations(NumberOfSamples) End If If ImperialInput = True Then CurrentElevationValue = CurrentElevationValue * 0.3048 CurrentRangeValue = CurrentRangeValue * 0.9144 End If
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CurrentElevationValue = CurrentElevationValue * 100 OutputElevation = CurrentElevationValue 'OutputString = OutputString & "Range: " & PreviousRange & "-" & CurrentRangeValue & ", Elevation: " & OutputElevation & "END" ' ********************** output range value ***************** pNRemap.MapRange PreviousRange, CurrentRangeValue, OutputElevation ' ********************** output range value ***************** PreviousRange = CurrentRangeValue Next Next ' Add the last line pNRemap.MapRange PreviousRange, Ranges(Samples - 1), 0 'OutputString = OutputString & "Range: " & PreviousRange & "-" & Ranges(Samples - 1) & ", Elevation: 0END" Set pRemap = pNRemap 'Set ReclassifyRaster = pReclassOp.Reclass(RasterToReclass, pRemapTable, "From", "To", "Out", True) Set ReclassifyRaster = pReclassOp.ReclassByRemap(RasterToReclass, pRemap, True) 'Set ReclassifyRaster = RasterToReclass Erh: 'MsgBox "Failed to Perform reclassification." & Err.Description & Err.Number End Function Function FloatDividedRaster(RasterToFloat As IRaster) As IRaster ' Get the Map 'Dim pMxDoc As IMxDocument 'Set pMxDoc = ThisDocument 'Dim pMap As IMap 'Set pMap = pMxDoc.FocusMap ' Get the input raster from the first layer in ArcMap 'Dim pLayer As ILayer 'Set pLayer = pMap.Layer(0) 'If Not TypeOf pLayer Is IRasterLayer Then ' Exit Function
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'End If 'Dim pRLayer As IRasterLayer 'Set pRLayer = pLayer Dim pInRaster As IRaster Set pInRaster = RasterToFloat ' Create a Spatial operator Dim pAlgbOp As IMapAlgebraOp Set pAlgbOp = New RasterMapAlgebraOp ' Set output workspace Dim pEnv As IRasterAnalysisEnvironment Set pEnv = pAlgbOp Dim pWS As IWorkspace Dim pWSF As IWorkspaceFactory Set pWSF = New RasterWorkspaceFactory Set pWS = pWSF.OpenFromFile(TEMPFiles, 0) Set pEnv.OutWorkspace = pWS ' Bind a raster Call pAlgbOp.BindRaster(pInRaster, "R1") ' Perform Spatial operation Set FloatDividedRaster = pAlgbOp.Execute("Float ([R1]) / 100") End Function Public Function OpenRasterDataset(sPath As String, sFileName As String) As IRasterDataset ' Returns RasterDataset object given a file name and its directory ' sPath: path of the input raster dataset ' sFileName: name of the input raster dataset On Error GoTo Erh Dim pWSFact As IWorkspaceFactory Dim pRasterWS As IRasterWorkspace Set pWSFact = New RasterWorkspaceFactory If pWSFact.IsWorkspace(sPath) Then Set pRasterWS = pWSFact.OpenFromFile(sPath, 0) Set OpenRasterDataset = pRasterWS.OpenRasterDataset(sFileName) End If Exit Function Erh: Set OpenRasterDataset = Nothing MsgBox "Failed in Opening RasterDataset. " & Err.Description End Function Public Sub AddRasterLayer(pRaster As IRaster) On Error GoTo Erh ' Adds a layer to an ArcMap session Dim pRasterLayer As IRasterLayer
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Set pRasterLayer = New RasterLayer pRasterLayer.CreateFromRaster pRaster Dim pMap As IBasicMap Dim pMxDoc As IMxDocument Dim pActView As IActiveView Set pMxDoc = ThisDocument Set pMap = pMxDoc.FocusMap Set pActView = pMxDoc.ActiveView pMap.AddLayer pRasterLayer pActView.Refresh pMxDoc.UpdateContents Exit Sub Erh: MsgBox "Failed to Add Raster Layer." & Err.Description End Sub Function SubtractCone(coneRaster As IRaster) As IRaster ' takes in trajectory cone and subtracts it from the DEM ' Open DEM ' open raster Dim OpenedDEM As IRasterDataset Set OpenedDEM = OpenRasterDataset(RASTERFiles, MAINDEM) Dim ConvertedRaster As IRaster Set ConvertedRaster = OpenedDEM.CreateDefaultRaster ' Create a Spatial operator Dim pMathOp As IMathOp Set pMathOp = New RasterMathOps ' Set output workspace Dim pEnv As IRasterAnalysisEnvironment Set pEnv = pMathOp Dim pWS As IWorkspace Dim pWSF As IWorkspaceFactory Set pWSF = New RasterWorkspaceFactory Set pWS = pWSF.OpenFromFile(TEMPFiles, 0) Set pEnv.OutWorkspace = pWS ' Perform the operation Set SubtractCone = pMathOp.Minus(ConvertedRaster, coneRaster) End Function Function GetVisibility(InputDEMSurface As IGeoDataset, CurrentFeature As Integer) As IRaster ' Get the Map Dim pMxDoc As IMxDocument Set pMxDoc = ThisDocument Dim pMap As IMap Set pMap = pMxDoc.FocusMap
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' Get the input source data from the first layer in ArcMap Dim pGeoDs As IGeoDataset Dim pLy As ILayer Dim ThisLayer As Integer ' counter for looping through layers Dim NoFeatures As Boolean ' checks whether the feature has been found NoFeatures = False For ThisLayer = 1 To (pMap.LayerCount) Set pLy = pMap.Layer(ThisLayer - 1) ' if the feature layer is found then use it If TypeOf pLy Is IFeatureLayer Then NoFeatures = False Exit For Else NoFeatures = True End If Next ThisLayer If NoFeatures = True Then MsgBox "The appropriate feature layer must be loaded." Exit Function End If Dim pFeatureLy As IFeatureLayer Set pFeatureLy = pLy Set pGeoDs = pFeatureLy.FeatureClass Dim CurrentID As Integer Dim CurrentField As String CurrentID = CurrentFeature CurrentField = FEATUREField Dim CurrentPoint As IFeatureClassDescriptor Dim sFieldName As String Dim pQueryFilter As IQueryFilter Set pQueryFilter = New QueryFilter ' Set the where clause pQueryFilter.WhereClause = CurrentField & " = " & CurrentID sFieldName = CurrentField Set CurrentPoint = New FeatureClassDescriptor CurrentPoint.Create pGeoDs, pQueryFilter, sFieldName ' Create the RasterSurfaceOp object Dim pSurfaceOp As ISurfaceOp Set pSurfaceOp = New RasterSurfaceOp ' Declare the input raster object Dim pElevation As IGeoDataset
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' Calls function to open a raster dataset from disk 'Set pElevation = OpenRasterDataset(RASTERFiles, MAINDEM) Set pElevation = InputDEMSurface ' Declare the input feature class object Dim pObservers As IGeoDataset ' Calls function to open a points dataset from disk 'Set pObservers = OpenFeatureClassDataset("D:\SpatialData", "observers") Set pObservers = CurrentPoint ' Declare the output raster object Dim pOutputRaster As IGeoDataset ' Calls the method Set GetVisibility = pSurfaceOp.Visibility(pElevation, pObservers, esriGeoAnalysisVisibilityFrequency) End Function Function RemoveNoData(InputRaster As IRaster) As IRaster 'On Error GoTo Err: ' Create a Spatial operator Dim pAlgbOp As IMapAlgebraOp Set pAlgbOp = New RasterMapAlgebraOp ' Set output workspace Dim pEnv As IRasterAnalysisEnvironment Set pEnv = pAlgbOp Dim pWS As IWorkspace Dim pWSF As IWorkspaceFactory Set pWSF = New RasterWorkspaceFactory Set pWS = pWSF.OpenFromFile(TEMPFiles, 0) Set pEnv.OutWorkspace = pWS ' Bind a raster Call pAlgbOp.BindRaster(InputRaster, "R1") ' Perform Spatial operation Set RemoveNoData = pAlgbOp.Execute("con(isnull ([R1]), 0, [R1])") 'Set RemoveNoData = InputRaster 'Err: 'MsgBox "buggered up again: " & Err.Description 'Exit Function End Function Function OpenTableFromDBFFile(dbfPath As String, dbfFile As String) As ITable Dim pMxDoc As IMxDocument Set pMxDoc = ThisDocument Dim pWorkspace As IWorkspace
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Dim pFact As IWorkspaceFactory Set pFact = New ShapefileWorkspaceFactory Set pWorkspace = pFact.OpenFromFile(dbfPath, 0) Dim pFWorkspace As IFeatureWorkspace Set pFWorkspace = pWorkspace Set OpenTableFromDBFFile = pFWorkspace.OpenTable(dbfFile) End Function Function ConvertRange(InputXValue As Long, InputYValue As Single, InputAngle As Single, OutputTheX As Boolean) As Single Dim OutputAngle As Single ' convert to angles the radial angle calulator understands OutputAngle = (InputAngle * -1) + 90 Dim AngleFromZero As Double Dim RotationAboutOrigin As Single Dim TrajHypotenuse As Double Dim pi As Double Dim NewX As Double Dim NewY As Double pi = 3.14159265358979 TrajHypotenuse = Sqr((InputXValue * InputXValue) + (InputYValue * InputYValue)) AngleFromZero = (Atn(InputYValue / InputXValue)) * (180 / pi) RotationAboutOrigin = OutputAngle - AngleFromZero NewX = TrajHypotenuse * Sin((RotationAboutOrigin) * (pi / 180)) NewY = TrajHypotenuse * Cos((RotationAboutOrigin) * (pi / 180)) If OutputTheX = True Then ConvertRange = NewX Else ConvertRange = NewY End If End Function
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