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he Manhattan Project in World War II developed the first atomic bomb. The project was led by theUnited States, with participation

from the United Kingdom and Canada. From 1942 to 1946 the project was under the command of Major General Leslie R. Groves Jr. of

the US Army Corps of Engineers. The Army component of the project was officially designated theManhattan District, US Engineer

Department, but was usually referred to as theManhattan Engineer District (MED). "Manhattan" gradually superseded the official

codename for the project.

Manhattan Engineer District (MED)

The Manhattan Project created the firstnuclear bombs. The first human-

engineered nuclear detonation, the Trinity test, is shown.

Active 1942±1946

Country United States

United Kingdom

Canada

Branch United States Army Corps of Engineers

Garrison/HQ Oak Ridge, Tennessee

Anniversaries 13 August 1942

Engagements Allied Invasion of It aly

Allied Invasion of France

Allied Invasion of Germany

Atomic bombings of Hiroshima and Nagasaki

Allied Occupation of Japan



Disbanded 31 December 1946

Commanders

Notable

commanders

Leslie R. Groves

Kenneth D. Nichols

Insignia

Shoulder patch of

the Manhattan

Engineer District,

which was adopted

in 1945

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0.71% to 0.89%. T his mater ial was f ed into the gaseous diff usion process in the K -25 plant, which produced a product enr iched to about

23%. This was, in turn, f ed into Y-12, which boosted it to about 85%, sufficient f or nuclear weapons. The more complex plutonium

core Fat Manimplosion-type nuclear weapon required a concer ted eff or t f rom a os Alamos scienti sts to design and construct. The first

was detonated at the Tr inity test in b uly 1945. Bombs developed by the pro ject were used in the atomic bombings of Hiroshima and

Nagasaki.

The c anhattan Pro ject was also charged with gather ing intelligence on the d erman nuclear energy pro ject. Through its Operation

Alsos it gathered nuclear mater ials and rounded up d erman scientists. The c Ee

maintained control over Amer ican atomic weapons

production until the f ormation of the United States Atomic Energy f ommission in b anuary 1947.

Contents

[hig

h

i

1 Or i p iq

r

2 Feasis

ilitt

o 2.1 Proposals

o 2.2 Bomb desi u

v

concepts

3 Organiw ation

o 3.1 Manhattan Engineer Distr ict

o 3.2 Military Policy Committee

o 3.3 Collaboration with Br itain

4 Pro ject sites

o 4.1 Oak Ridge

o 4.2 Los Alamos

o 4.3 Argonne

o 4.4 Hanford

o 4.5 Trail

o 4.6 Chalk Rix

er

5 R aw mater ials

6 Uraniy m

o 6.1 Electromagnetic separation

o 6.2 Gaseous diffusion

o 6.3 Thermal diffusion

o 6.4 Weapon design

7 Plutonium

o 7.1 R eactor design

o 7.2 Thin Man

o 7.3 Separation process



o 7.4 Metallurgy

o 7.5 Weapon design

o 7.6 Tr inity

8 Foreign Intelligence

9 Bombing of Hiroshima and Nagasak i

o 9.1 Preparations

o 9.2 The use of the bombs

10 Post � War

11 Cost of the Manhattan Pro ject

12 Notes

13 R eferences

[edit]Or igins

In 1939, President �

ranklin � oosevelt called on �

yman Br iggs of the National Bureau of Standards to head the Advisory �

ommittee on

Uranium to investigate the issues raised by the Einstein±Szilárd letter . Br iggs held a meeting on 21 October 1939 which was attended

byLeo Szilard, Edward Teller and Eugene �

igner . The committee repor ted to � oosevelt in November that "it would provide a possible

source of bombs with a destructiveness vastly greater than anything now known." [1] Br iggs proposed that the National � ef ense

� esearch �

ommittee (N� �

�

) spend $167,000 on aspects of uranium research, par ticular ly into the uranium-235 isotope and recently

discoveredplutonium. On 28 � une 1941, � oosevelt signed Executive Order 8807 which created the Office of Scientific � esearch and

� evelopment(OS� � ), with Vannevar Bush as its director . The office was empowered to engage in large engineer ing pro jects in addition

to research. [2]The N� �

�

�

ommittee on Uranium became the S-1 Uranium �

ommittee of the OS� �

; the word "uranium" was soon

dropped f or secur ity reasons. [3]

� eanwhile, in the United Kingdom, Otto �

r isch and � udolf Peier ls at the University of Birmingham made a breakthrough investigating

thecr itical mass of uranium-235.[4] Their calculations indicated that it was within an order of magnitude of ten kilograms, which was small

enough to be carr ied by a bomber of the day. [5] The � arch 1940�

r isch±Peier ls memorandum resulted in the setting up of the

Br itish � aud �

ommittee, which concluded that:

(i) The committee considers that the scheme f or a uranium bomb is practicable and likely to lead to decisive results in the war

(ii) It recommends that this work continue on the highest pr ior ity and on the increasing scale necessary to obtain the weapon in the

shor test possible time

(iii) That the present collaboration with Amer ica should be continued and extended especially in the region of exper imental w ork.[6]

One of the members of the � aud �

ommittee, the Australian physicist � arcus Oliphant, flew to the United States in late August 1941 to

find out why the US was apparently ignor ing the committee's findings. He repor ted, "[T]his inar ticulate and unimpressive man [Br iggs]

had put the repor ts in his saf e and had not shown them to members of his committee."[7] Oliphant met with the Uranium �

ommittee and

visited Berkeley,�

alif ornia where he met with Ernest O. Lawrence and other physicists. Oliphant's eff or ts to galvanize the Amer icans

into action were successf ul. Lawrence in par ticular was inspired, and resolved to turn his old 37-inch cyclotron into a giant mass

spectrograph.[8]



At a meeting between President Roosevelt, Bush andVice President � enry A. Wallace on 9�

ctober 1941, the President approved the

atomic program. To control it, he created a Top Policy Group consisting of himself ²although he never attended a meeting²Wallace,

Bush, James B. Conant, Secretary of War � enry L. Stimson and the Chief of Staff of the Army, General George C. Marshall. The Army

would have principal responsibili ty for the project. Roosevelt also agreed to coordinate the effort with that of the Briti sh, and on 11

�

ctober he sent a message to thePrime Minister of the United Kingdom, Winston Churchill suggesting that they correspond on atomic

matters.[9]

[edit]Feasibility

A 194�

meeting at Berkeley with�

from left to right)Ernest�

. Lawrence, Arthur �

. Compton, Vannevar Bush, James B. Conant, Karl T. Compton and Alfred

L. Loomis

[edit]Proposals

The S-1 Commit tee held its first meeting on 1� December "pervaded by an atmosphere of enthusiasm and urgency"[1�

] in the wake of

the attack on Pearl � arbor and the subsequent declaration of war by the United Stateson Germany and Japan. Work was proceeding

on three different techniques for isotope separation to separate uranium-2�

� from uranium-2�

� . Lawrence and his team at

the University of California, Berkeleyinvestigated electromagnetic separation, whileEger Murphree and Jesse Wakefield Beams' team

looked into gaseous diffusion at the University of Columbia, and Philip Abelson directed research into liquid thermal diffusionat

the Carnegie Institution of Washingtonand later the � aval Research Laboratory.[11]

Meanwhile, there were two lines of research into reactor technology, with� arold Urey continuing research into heavy water at

Columbia, while Arthur Comptonbrought the scientists working under his supervision at Columbia Universityand Princeton University to

the University of Chicago, where he organi ed the University of Chicago Metallurgical Laboratoryin early 1942 to

study plutonium and nuclear reactors usingnuclear graphite as a neutron moderator .[12] Briggs, Compton, Lawrence, Murphree and Urey

met on 2�

May to finali e the S-1 Commi ttee recommendations, which called for all f ive technologies to be pursued. This was approved

by Bush, Conant and Brigadier General Wilhelm D. Styer , the Chief of staff of Major General Brehon B. Somervell's Services of Supply,

who had been designated as the Army's representative. They took the recommendation to the Top Policy Group with a budget proposal

for �

4 million for construction by theUnited States Army Corps of Engineers,

�

1 million for research and development by�

SRD and

� million for contingencies in fiscal year 194

�

. The Top Policy Group sent it to the President on 1

June 1942 and he approved it by

writing "�

K FDR" on the document.[11]

[edit]Bomb design concepts



Different fission bomb assembly methods explored during the July 1942 conference

Compton asked the theoretical physicist J. Robert ppenheimer of the University of California, Berkeley to take over research onfast

neutron calculations²the key to calculations of critical m assand weapon detonation²from Gregory Breit, who had quit because of

concerns over lax operational security on 1

May 1942.[1

] Johnj

. Manley, a physicist at the Metallurgical Laboratory, was assigned to

assist

ppenheimer by contacting and coordinating experimental physics groups scattered across the country.[14]

ppenheimer

and Robert Serber of the University of Illinois examined the problems of neutron diffusion²how neutrons moved in a nuclear chain

reaction²and hydrodynamics²how the explosion produced by a chain reaction might behave. To review this work and the general

theory of fission reactions, ppenheimer convened meetings at the University of Chicago in June at the University of California,

Berkeley, in July 1942 with theoretical physicists j ans Bethe, John Van Vleck, Edward Teller , Emil Konopinski, Robert Serber, Stan

Frankel, and Eldred C.k

elson, the latter three former students of

ppenheimer, andexperimental physicists Felix Bloch, Emilio Segrè,

John Manley and Edwin McMillan. They tentatively confirmed that a fission bomb was theoretically possible.[1l

]

There were sti ll many unknown factors. The properties of pure uranium-2m

n were relatively unknown, as were those of plutonium, a new

element which had only been discovered in February 1941 byGlenn Seaborg and his team. The product of uranium-2m

absorbing a

neutron which had been emit ted from a fissioning uranium-2m

n atom, it was thus able to be created in a nuclear reactor. But at this point

no reactor had been built. nly tiny quantities of plutonium were available, produced from neutrons derived from reactions started in

a cyclotron.[16] Even by December 194m

, only two milligrams had been produced.[1o

]The scientists at the Berkeley conference

determined that there were many ways of arranging the fissile material into a critical mass. The simplest was shooting a "cylindrical

plug" into a sphere of "active material" with a "tamper"²dense material that would focus neutrons inward and keep the reacting mass



together to increase its efficiency. [18] They also explored designs involving spheroids, a pr imitive f orm of "implosion" suggested

by

ichard

. Tolman, and the possibility of autocatalytic methods , which would increase the efficiency of the bomb as it exploded. [19]

onsider ing the idea of the fission bomb theoretically settled²at least until more exper imental data was available²the Berkeley

conf erence then turned in a diff erent direction. Edward Teller pushed f or discussion of a more power f ul bomb: the "super", no w usually

ref erred to as a " hydrogen bomb", which would use the explosive f orce of a detonating fission bomb to ignite a nuclear f usion reaction

in deuter ium and tr itium.[20] Teller proposed scheme after scheme, but Bethe ref used each one. The f usion idea was put aside to

concentrate on producing fission bombs. [21] Teller also raised the speculative possibility that an atomic bomb might "ignite" the

atmosphere because of a hypothetical f usion reaction of nitrogen nuclei. [22] Bethe calculated that it could not happen, [23] and a repor t co-

authored by Teller showed that "no self -propagating chain of nuclear reactions is likely to be star ted."[24] In Serber's account,

Oppenheimer mentioned it to Ar thur

ompton, who "didn't have enough sense to shut up about it. It somehow got into a document that

went to ashington" which led to the question bei ng "never laid to rest". [25]

[edit]Organization

[edit]Manhattan Engineer i

tr i t

The

hief of Engineers, a jor

eneral Eugene

eybold selected

olonel

ames

. arshall to head the Army's par t of the pro ject in

une 1942. arshall created a liaison office in ashington,

.

. but established his temporary headquar ters on the 18th floor of 270

Broadway in New York

ity, where the

orps of Engineers' Nor th Atlantic

ivision was located. This allowed him to draw on it f or

administrative suppor t. It was close to the anhattan office of Stone & ebster , the pr incipal pro ject contractor , and to

olumbia

University. It was temporary because arshall intended to later relocate to the ma jor construction site. He had permission to draw on

his f ormer command, the Syracuse

istr ict, f or staff, and he star ted with Lieutenant

olonel Kenneth

. Nichols, who became his

deputy.[26][27]

Because most of his task involved construction, arshall worked in cooperation with the head of the

orps of Engineers

onstr uction

ivision,

a jor

eneral Thomas

.

obbins and his deputy,

olonel Leslie

.

roves,

r .

eybold, Somervell and Styer decided to call

the pro ject "Development of Substitute ater ials", but

roves f elt that this would draw attention. Since engineer distr icts n ormally

carr ied the name of the city where the y were located, arshall and

roves agreed to instead name it the anhattan Distr ict. This

became official on 13 August, when

eybold issued the order creating the new distr ict. Unlike other distr icts, it had no geog raphic

boundar ies, and arshall had the author ity of a division engineer . "Development of Substitute ater ials" remained as the pro ject

codename, but was supplanted over time by "Manhattan". [27]

Marshall later conceded that "I had never never heard of atomic fission but I did know that you could not build much of a plant, much

less f our of them f or $90 million."[28] A single TNT plant that Nichols had recently built in Pennsylvania had cost $128 million.[29] Nor were

they impressed with estimates to the nearest order of magnitude, which

roves compared with telling a caterer to prepare f or between

ten and a thousand guests. [30] A survey team f rom Stone & ebster had already scouted a site f or the production plants. The ar

Production Board recommended sites in the Knoxville, Tennessee area, an isolated area where the Tennessee Valley Author ity could

supply ample electr ic power and the r ivers could provide cooling water f or the reactors. After examining several sites, the s urvey team

selected one at Oak

idge, Tennessee.

onant advised that it be acquired at once and Styer agreed but Marshall tempor ized, awaiting

the results of

onant's reactor exper iments bef ore taking action. [31] Of the prospective processes, only Lawrence's electromagnetic

separation appeared sufficiently advanced f or construction to commence. [32]



Marshall andz

ichols began assembling the resources that they would need. The first step was to obtain a high priority ratingfor the

project. The top ratings were AA-1 through AA-4 in descending order, although there was alsoa special AAA rating reserved for

emergencies. Ratings AA-1 and AA-2 were for essential weapons and equipment, so ColonelLucius D. Clay, the deputy chief of staff at

Services and Supply for requirements and resources, felt that t he highest rating he could assign was AA-{ , although he was willing to

provide a AAA on request for critical materials if the need arose.

[33]

This was disappointing, for AA-3 was the same priority as

z

ichols'

Tz

T plant in Pennsylvania.[34]

[edit]Military Policy Committee

J. Robert|

ppenheimer and Leslie Groves at remains of the Trinity test in September 194}

. The white o vershoes prevent fallout from sticking to the soles of

their shoes.

Bush became dissatisfied with Colonel Marshall's failure to get the project moving forward expeditiously, specifically the failure to

acquire the Tennessee site, the low priority allocated to the project by the Army, andthe location of his headquarters inz

ew York

City.[35] Bush spoke to General Marshall, Somervell, Styer and~

arvey Bundy about his concerns. Bush felt that more aggressive

leadership was required. ~ e wanted the project placed under a senior policy committee, with a prestigious officer, preferablyStyer, as

overall director.[34]

Somervell and Styer selected Groves for the post, informing him on 1 September of this decision, and that General Marshall ordered

that he be promoted tobrigadier general,[36] as it was felt that the title "general" would hold m ore sway with the academic scientists

working on the Manhattan Project.[37]Groves orders placed him directly under Somervell ratherthan Reybold, with Colonel Marshall now

answerable to Groves.[38] Groves established his headquarters in Washington, D.C. on the fifth floor of thez

ew War Department

Building in Washington, D.C., where Colonel Marshall had his liaison office.[39] ~ e assumed command of the Manhattan Project on 23

September. Later that day, he attended a meeting called by Stimson which established a Military Policy Committee, responsible to the

Top Policy Group, consisting of Bush, with Conant as an alternate, Styer andRear Admiral William R. Purnell.[36] Tolman and Conant

were later appointed as Groves' scientific advisers.[4

]

n 19 September Groves went to Donaldz

elson, the chairman of the War Production Board and asked for broad authority to issue a

AAA rating whenever it was required.z

elson initially balked but quickly caved in when Groves threatened to go to the



President.[41] roves promised not to use the AAA rating u nless it was necessary. It soon transpired that f or the routine requirements of

the pro ject the AAA rating was too high but the AA -3 rating was too low. After a long campaign, roves finally received AA -1 author ity

on 1

uly 1944. [42]

One of roves' ear ly problems was to find a director f or Pro ject Y, the group that would design and build the bomb. The obvio us choice

was one of the three laboratory heads, Urey, Lawrence and ompt on. However , they could not be spared. ompton recommended

Oppenheimer , but he had two drawbacks. Unlike those three, Oppenheimer had not won a Nobel Pr ize and many scientists f elt that the

head of such an impor tant laboratory should have one. There was also concern about whether was he a secur ity r isk, as many of

Oppenheimer's associates were communists, including his brother Frank Oppenheimer , his wif e Kitty and his gir lf r iend

ean Tatlock. A

long conversation on a train in October 1942 convinced roves and Nichols that Oppenheimer thoroughly understood the issues

involved in setting up a laboratory in a remote area and should be appointed as its director . roves personally waived the se cur ity

requirements and issued Oppenheimer with a clearance on 20

uly 1943. [43][44]

[edit]Collaboration with r itain

The Br itish and Amer icans exchanged nuclear inf ormation but did not initially pool t heir eff or ts. The Br itish rebuff ed eff or ts by Bush and

onant in 1941 to strengthen cooperation with the Br itish pro ject, code-named Tube Alloys.[45] However , Br itain did not have the

manpower or resources of the United States, and despite its ear ly and promising star t, the Br itish pro ject soon f ell behind i ts Amer ican

counterpar t. On 30

uly 1942, Sir

ohn Anderson, the minister responsible f or Tube Alloys, advised hurchill that: "We must f ace the

f act that... [our ] pioneer ing work... is a dwindling asset and that, unless we capitalize it quickly, we shall be outstr ipped. We now have a

real contr ibution to make to a 'merger .' Soon we shall have little or none." [46] By this time, the Br itish bargaining position had worsened,

and their motives were mistrusted by the Amer icans. ollaboration theref ore lessened markedly, and the exchange of inf ormatio n

stopped.[47]

In August 1943 hurchill and

oosevelt negotiated the Quebec Agreement, which resulted in a resumption of cooperation. [48] The

subsequent Hyde Park Agreement in September 1944 extended this cooperation to the post -war per iod.[49] The Quebec Agreement

established the ombined Policy ommittee to coordinate the eff or ts of the United States, Br itain and anada. Stimson, Bush and

onant served as the Amer ican members of the ombined Policy ommittee; Field Marshal Sir

ohn Dill and olonel

.

.

Llewellin were the Br itish members; and . D. Howe was the anadian member .[50] Llewellin returned to the United Kingdom at the end

of 1943 and was replaced on the committee by Sir

onald Ian ampbell, who in turn was replaced by the Br itish Ambassador to the

United States, Lord Halif ax, in ear ly 1945. Sir

ohn Dill died in Washington, D. . in November 1944 and was replaced both as hief of

the Br itish

oint Staff Mission and as a member of the ombined Policy ommittee by Field Marshal Sir Henry Maitland W ilson.[51]

ames hadwick pressed f or Br itish involvement in the Manhattan Pro ject to the f ullest extent. W ith hurchill 's backing, he attempted to

ensure that every request f rom roves f or assistance was honored. [52] The Br itish Mission that arr ived in the United States in December

1943 included Niels Bohr , Otto Fr isch, Klaus Fuchs,

udolf Peier ls and Ernest Titter ton.[53]

Par t of Quebec Agreement specified that

nuclear weapons would not be used against another country without mutual consent. In

une 194 5 W ilson agreed that the use of

nuclear weapons against

apan would be recorded as a decision of the ombined Policy ommittee. [54]

The ombined Policy ommittee created the ombined Development Trust in

une 1944, with roves as its chairman, to

procure uranium and thor ium ores on international markets. In 1944, the ombined Development Trust purchased 3,440,000 pounds

(1,560,000 kg) of uranium oxide ore f rom companies operating mines in the Belgian ongo. In order to avoid br iefing US Secretary of

the Treasury Henry Morgenthau

r . on the pro ject, a special account not sub ject to the usual auditing and controls was used to hold



Trust monies. Between 1944 and the time he resigned from the Trust in 1947, Groves deposited a total of

37.5million into the Trust's

account.[55]

[edit]Project sites

A selection of U.S. sites important to the Manhattan Project. Click on the location for more information.

[edit]Oak Ridge

The day after he took over the project, Groves and Colonel Marshall took a train to Tennessee to inspect the site for the proposed

production plant at

ak Ridge. Groves was suitably impressed.[56]

n 29 September, United States Under Secretary of WarRobert P.

Patterson authori ed the Corps of Engineers to compulsorily acquire 56,� � �

acres � 23,� � �

ha) of land at a cost of

3.5million. An

addition 3,� � �

acres � 1,2� �

ha) was subsequently acquired. About 1,� � �

fami lies were affected by the condemnation order which came

into effect on 7 ctober.[57] Protests, legal appeals, and a 1943 congressional inquiry were to no avail.[58] By mid-�

ovember US

Marshals were tacking notices to vacate on farmhouse doors, and construction contractors were movingin.[59] Some families were given

two weeks' notice to vacate family farms that had been their homes for generations;[6

�

] others had settled there after being evicted to

make way for the Great Smoky Mountains�

ational Park in the 192� s or the

�

orris Dam in the 1930s.[58] The ultimate cost of land

acquisition in the area, which was not completed until March 1945, was only about

2.6mil lion, which worked out to around

47 an

acre.[61] When presented with Public Proclamation�

umber Two, which declared ak Ridge a total exclusion one, theGovernor of

Tennessee,Prentice Cooper , angrily tore it up.[62]

The population of ak Ridge peaked at 75,000 in May 1945, at which time 82,000 peoplewere employed at the Clinton Engineering

Works.[63] The Chief of the Central Facilities Division, Clinton Engineering Works, was effectively the mayor of the town. The post was

held by Lieutenant Colonel Thomas T. Crenshaw from ctober 1942 to May 1944 and then Lieutenant Colonel John S. � odgson from

May 1944 to January 1946.[64]

Captain Paul E. 'Meara was town manager.[65]

The Army presence at ak Ridge increased in August

1943 when�

ichols replaced Marshall as head of the Manhattan Engineer District. ne of his f irst taskswas to move the distr ict



headquarters to�

ak Ridge although the name of the district did not change.[66] In September 1943 the administration of community

facilities was outsourced to Turner Construction Company through a subsidiary known as the Roane-Anderson Company

after Anderson and Roanecounties, in which�

ak Ridge was located.By 1945 it employed some 10,000 people.[67]

[edit]Los Alamos

Wikisource has original

text related to this article:

Los Alamos Ranch

School Seizure Letter

The idea of locating Project Y at ak Ridge was considered, but in the end itwas decided to locate it in a remote, isolated location. n

ppenheimer's recommendation, the search for a suitable site was narrowed to the vicinity of Albuquerque, ew Mexico, where

ppenheimer owned a ranch. In

ctober 1942, Major John

. Dudley of the Manhattan Project was sent to survey the area, and he

recommended a site near Jeme Springs, ew Mexico. [68] n 16 ovember 1942, ppenheimer, Groves, Dudley and others toured the

site. ppenheimer feared that the high cliffs surr ounding the site would make his people feelclaustrophobic, while the engineers were

concerned with the possibility of flooding. The party then moved on to the vicinity of theLos Alamos Ranch School. ppenheimer was

impressed and expressed a strong preference for the site.[69] The engineers were concerned about the poor access road and the water

supply, but otherwise felt that it was ideal.[70]

Patterson approved the acquisition of the site on 25 ovember 1942, authori ing

440,000 for the purchase of the 54,000-acre 22,000

ha) site, all but 8,900acres 3,600 ha) of which were already owned by the Federal Government.Secretary of Agriculture Claude R.

Wickard authori ed the War Department's use of some 46,000acres

19,000 ha) of United States Forest Service land "so long as the

military necessity continues". The need for land for a new road, and later for aright of way for a 25 miles 40 km) power line, eventually

brought wartime land purchases to 45,737acres 18,509 ha), but only

414,971 was spent.[71]

Construction was contracted to the M. M. Sundt Company of Tucson, Ari ona, with Will ard C. Kruger and Associates of Santa Fe, ew

Mexico as architect and engineer. Work commenced in December 1942. Groves initially allocated

300,000 for construction, three times

ppenheimer's estimate, with an estimated completion date of 15 March 1943. It soon became clear that the scope of Project Y was

greater than expected, and by the time Sundt finished in 30 ovember 1943, over

7million had been spent.[72]

The first post commander was Lieutenant Colonel John M. arman, who was relieved after a series of disagreements with the

scientists. e was succeeded by Lieutenant Colonel Whitney Ashbridge, a graduate of theLos Alamos Ranch School, in May 1943.

Ashbridge suffered a mild heart attack in ctober 1944 and was replaced by Colonel George R. Tyler.[73][74]

Because it was secret, Los

Alamos was referred to as "Site Y" or "the ill".[75] Birth certificates of babies born in Los Alamos during the war had their place of birth

listed as P Box 1663 in Santa Fe.[76] Initially Los Alamos was supposed to be a military laboratory with ppenheimer and other

researchers commissioned into the Army. ppenheimer went so far as to order himself a lieutenant colonel's uniform, but two key

physicists, Robert Bacher and Isidor Rabi balked at the idea. As a result, Conant, Groves and ppenheimer devised a compromise

whereby the laboratory was operated by the University of California under contract to the War Department.[77]

[edit]Argonne



Shift change at the Y-12 uranium enrichment facility at

ak Ridge.

An Army- SRD meeting on 25 June 1942 decided tobuild a pilot plutonium plant in t he Argonne Forest southwest of Chicago. In July,

ichols arranged for a lease of 1,000acres 400 ha) from Cook County, Illinois and Captain James F. Grafton was appointed Chicago

area engineer. It soon became apparent that the scale of operations was too great for the Argonne, and plans were redrawn to locate

the pilot plant at ak Ridge.[78]

Delays in establishing Argonne led Compton to authori�

e construction of the first nuclear reactor beneaththe bleachers of Stagg

Field at the University of Chicago. n 2 December 1942 a team led byEnrico Fermi, initiated the first artificial[79] self-sustaining nuclear

chain reaction in an experimental reactor known as Chicago Pile-1. The point at which a reaction becomes self -sustaining became

known as "going critical". Compton reported the success to Conant in Washington, D.C. by a coded phonecall, saying, "The Italian

navigator [Fermi] has just landed in the new world."[80] In January 1943, Grafton's successor, Major Arthur V. Peterson, ordered Chicago

Pile-1 dismantled and reassembled at Argonne, as he regarded the operation of a reactor as too potentially ha�

ardous for a densely

populated area.[81]

[edit]Hanford

By December 1942 there were concerns that even ak Ridge was too close toKnoxville, Tennessee in the unlikely but possible event

of a major nuclear accident. Groves recruitedDuPont in

ovember 1942 to be the prime contractor for the construct ion of the plutonium

production complex. DuPont was offered a standardcost-plus fixed fee contract, but the President of the company,Walter S. Carpenter,

Jr., wanted no fee or profit of any kind, and asked for the proposed contract to be amended to explicitly exclude the company fr om

acquiring any patent rights. This was accepted, but for legal reasons a nominal profit of one dollar was agreed upon. After the war,

DuPont asked to be released from the contract early, and had to retur n 33 cents.[82]



Reactor B under construction at the�

anford site

DuPont recomm ended that the site be located far from the existing uranium production faci lity at�

ak Ridge.[83] In December 1942,

Groves dispatched Colonel Franklin Matthias and DuPont engineers to scout potential sites. Matthias reported that�

anford

Site near Richland, Washington was "ideal in virtually all respects". It was isolated and near theColumbia River , which could supply

sufficient water to cool the reactors which would produce the plutonium. Groves visited the site in January and established the�

anford

Engineer Works�

�

EW), codenamed "Site W". Under Secretary Patterson gave his approval on 9 February, allocating�

5million for the

acquisition of 40,000acres�

16,000 ha) of land in the area.[84] The federal government relocated some 1,500 residents of White

Bluffs and�

anford, and nearby settlements, as well as theWanapum and other tribes using the area. A dispute arose with farmers over

the issue of crops which had already been planted before the land was acquired, for which the farmers expected compensation.Where

schedules allowed, the Army allowed the crops to be harvested, but this was not always possible.[84] The land acquisition process

dragged on and was not completed before the end of the Manhattan Project in December 1946.[85]

This did not delay work. Although progress on the reactor design at Metallurgical Laboratory and DuPont was not sufficiently advanced

to accurately predict the scope of the project, a start was made in April 1943 on facilities for an estimated 25,000 workers,half of whom

were expected to live on site. By July 1944, some 1,200 buildings had been erected and nearly 51,000 people were living in the

construction camp. As area engineer, Colonel Matthias exercised overall control of the�

anford site.[86] At its peak, the construction

camp was the third most populous town in Washington state.[87] �

anford operated a fleet of over 900buses, m ore than the city

of Chicago.[88] Like Los Alamos and�

ak Ridge, Richland was a gated community, with restricted access.�

owever it looked outwardly

more like a typical wartime Americanboomtown, because the military profile was lower, and physical security elements like high fences

and guard dogs were less evident.[89]

[edit]Trail

Cominco had produced electrolytic hydrogen at Trail, British Columbiasince 1930. Urey suggested in 1941 that it could produceheavy

water . To the existing�

10M plant consisting of 3,215 cells consuming 75MW of hydro-electric power was added secondary electrolysis

cells to increase the deuterium concentration in the water from the exchange process from 2.3% to 99.8%. For this process,�

ugh

Taylor of Princeton developed a platinum on carbon catalyst for the first three stages while Urey developed a nickel-chromia one for the

fourth stage tower. The final cost was�

2.8million. The Canadian Government did not officially learn of the project until August 1942.



Trail heavy water production started in January 1944 and continued until 1956. eavy water from Trail was used for the Argonne

reactor²the fi rst heavy water/natural uranium reactor²which went crit ical on 15 May 1944.[90]

[edit]Chalk River

The Chalk River, ntario site was established to house the Allied effort that was going on atMcGill Universityat the Montreal

Laboratory. Since the site was 120miles 190 km) west of ttawa, a new community was built atDeep River, ntario to provide

residences and facilities for the team members. The site was chosen for its proximity to the industrial manufacturing of ntario and

uebec, and access to a rail head adjacent to a large military base,Camp Petawawa. Located on the ttawa River it had access to

abundant water. The first director of the new laboratory was John Cockroft, but he was later replaced byBennett Lewis. A pilot reactor

known ZEEP Zero-energy experimental pile) became the first Canadian reactor, and the first to be completed outside the United

States, when it went critical in September 1945. A larger 10MW RX reactor which was designed during the war was completed and

went critical in July 1947.[90]

[edit]Raw materials

A billboard encouraging secrecy amongst

ak Ridge workers.

ichols arranged with the State Department for export controls to be placed onuranium oxide and negotiated for the purchase of 1,200

tons of ore from theBelgian Congo in a warehouse on Staten Island. e arranged with Eldorado Mining and Refiningfor the purchase

of ore from its mine inPort

ope,

ntario and its shipment in 100-ton lots.[91] Mallinckrodt Incorporated in St Louis, Missouri took the

raw ore, dissolved it innitric acid to produce uranyl nitrate. Ether was then added. As this has a greater affinity for ether than water, and

the two liquids do not mix,liquid-liquid extraction was used to separate uranyl nitrate from the impurities. This was then heated to

form uranium trioxide, which was reduced to highly pure uranium dioxide.

[92]

By July 1942, Mallinckrodt was producing a ton of highly

pure oxide a day, but turning this into uranium metal initially proved more difficult for Westinghouse and Metal ydrides.[93] Production

was too slow and quality was unacceptably low. A special branch of the Metallurgical Laboratory was established atIowa State

College in Ames, Iowaunder Frank Spedding to investigate alternatives. They developed the Ames process, which became available in

1943.[94]

Marshall and

ichols discovered that the electromagnetic process would require 5,000 tons of copper , which was in desperately short

supply. owever, silver could be substituted, in an 11:10 ratio. n 3 August, ichols met withUndersecretary of the Treasury Daniel W.



Bell and asked for the transfer of 6,000 tons of silver bullion fromthe West Point Depository. "Young man," Bell told him, "you may think

of silver in tons but the Treasury will always think of silver introy ounces!"[95]

Eventually, 14,700 tons would be used. The 1,000-ounce

28,000 g) silver bars were cast into cylindrical billets and taken toPhelps Dodge in Bayway, ew Jersey where they were extruded into

strips 0.625 inches 15.9 mm) thick, 3 inches 76 mm) wide and 40 feet 12 m) long. These were wound ontomagnetic coils by Allis

Chalmers in Milwaukee, Wisconsin. After the war, all the machinery was dismantled and cleaned and the floorboards beneath the

machinery were ripped up and burned to recover minute amounts of silver. In the end, only 1/36,000th of a percent was lost.[96][97]

The

last silver was returned in May 1970.[98]

[edit]Uranium

[edit]Electromagnetic separation

atural uranium consists of 99.3% uranium-238 and only 0.7% uranium-235, but only the latter isfissile. The rarer but chemically

identical uranium-235 has to be physically separated from the more plentiful isotope. Various physical m ethods were considered

for uranium enrichment, most of which was carried out at ak Ridge.[99] Electromagnetic isotope separation was developed by

Lawrence at the University of California Radiation Laboratory. This method employed devices known as thecalutron, which was a

hybrid of the familiar laboratorymass spectrometer and cyclotron. The name was derived from the words "California", "university" and

"cyclotron".[100] The electromagnetic process was based upon the fact that charged particles are deflected in amagnetic field and the

amount of deflection depends upon the particle's mass.[101] The process was neither scientifically elegant nor industrially

efficient.[102] Indeed it was reckoned that compared with a gaseous diffusion plant or a nuclear reactor, an electromagnetic separation

plant would consume more scarce materials, require more manpower to operate and cost more to build. onetheless, it was approved,

primarily because it was based on proven technology and therefore represented less risk. Moreover, it could be built in stages and

rapidly reach industrial capacity.[100] It also had the backing of Lawrence, the value of which should not be underestimated.[103]

Giant Alpha I racetr ack at Y-12.

Responsibility for the design and construction of the electromagnetic separation plant, which came to be calledY-12, was assigned to

Stone & Webster by the S-1 Committee in June 1942. The design called for f ive first stage processing units, known as Alpharacetracks,

and two units for final processing, known as Beta racetracks. In September 1943 Groves authori ed construction of four more

racetracks, known as Alpha II. Construction began in February 1943. Major Wilbur E. Kelley was placed in charge of Y-12.[104] When the

plant was started up for testing on schedule in ctober, the 14-ton vacuum tanks crept out of alignment due to the power of the



magnets. As a result, t hey were fastened more securely.ª

owever, a more serious problem arose when the magnetic coils kept shorting

out. In December Groves ordered a magnet to be broken open. Kelley reached inside and removed handfuls of rust. Groves then

ordered the racetracks to be torn down and all the magnets were sent back to the factory to be cleaned. A pickling plant was

established on site to clean the pipes and fittings.[102]

As a result, the first Alpha I racetrack was not operational until March 1944.

ª

owever the second Alpha I was operational by the end of January 1944, the first Beta and third Alpha I came online in March,and the

fourth Alpha I was operational in April.The four Alpha II racetracks were completed between July and«

ctober 1944.[105]

¬

perators at their calutroncontrol panels at the Y-12. Gladys¬

wens, the woman seated in the foreground, did not reali e what she had been doing until

seeing this photo in a public tour of the facility fifty years later.

Tennessee Eastman was hired to manage Y-12 on the usual cost-plus fixed fee basis, with a fee of ®

22,500 per monthplus®

7,500 per

racetrack for the first seven racetracks and®

4,000 per additional racetrack.[106] The calutrons were initially operated by scientists from

Berkeley to remove bugs and achieve a reasonable operating rate. They were then turned over to trained Tennessee Eastman

operators who had only a high school education. ̄

ichols compared unit production data, and pointed out to Lawrence that the young

"hillbilly" girl operators were outperforming his PhDs. They agreed to a production race and Lawrence lost, a morale boost for the

Tennessee Eastman workers and supervisors. The girls were "trained like soldiers not to reason why", while "the scientists could not

refrain from time-consuming investigation of the cause of even minor fluctuations of the dials."[107]

Y-12 shipped its fi rst few hundred grams of 13 to 15% enriched uranium to Los Alamos in March 1944.«

nly 1 part in 5,825 of the

uranium feed emerged as final product. Much of the rest was splattered over equipment in the process. Strenuous recovery efforts

helped raise the enrichment of the product to 10% in January 1945. Groves was not satisfied and ordered ̄

ichols to remove Kelley.

Kelley swapped places with Major John R. Ruhoff, the head of the MED's Manhattan office. In February 1945 the Alpha racetracks

began receiving slightly enriched ° 1.4%) feed f rom the new S-50 thermal diffusion plant. The next month it received enhanced ° 5%) feed

from the K-25 gaseous diffusion plant. By Apri l K-25 was producing uranium sufficiently enriched to feed directly into the Beta tracks.[108]

[edit]Gaseous diffusion

The most promising but also the most challenging method of isotope separation wasgaseous diffusion. This is based on Graham's law,

which states that the rate of effusion of a gas is inversely proportional to the square root of itsmolecular mass. In a box containing a

semi-permeable membrane and a mixture of two gases, the lighter molecules will pass out of the container more rapidly than the

heavier molecules. The gas leaving the container is somewhat enriched in thelighter molecules, while the residual gas is somewhat



depleted. The idea was that such boxes could be formed into a cascade of pumps and membranes, with each successive stage

containing a slightly more enriched mixture. Research into the process was carried out at Columbia University by a group that included

± arold Urey, Karl P. Cohen and John R. Dunning.[109]

²

ak Ridge K-25 Plant

In³

ovember 1942 the Military Policy Committeeapproved the constriction of a 600-stage gaseous diffusion plant.[110] ́ n 14

December, M.W. Kellogg accepted an offer to construct t he plant, which was codenamed K-25. A cost plus fixed fee contract was

negotiated, proving for a fee of µ 2.5million. A separate corporate entity called Kellex was created for the project, headed by Percival C.

Keith, one of Kellogg's vice presidents.[111] The process faced formidable technical difficulties. The highly corrosive gasuranium

hexafluoride would have to be used, as no substitute could be found. The motors and pumps would have to be vacuum tight and

enclosed in inert gas. But the biggest problem was the design of the barrier, which would have to be strong, porous and resist to

corrosion by uranium hexafluoride. Electro-deposited nickel mesh diffusion barriers were pioneered by Edward Adler and Edward

³

orris. A six-stage pilot plant was built at Columbia to test the process. Unfortunately, the³

orris-Adler prototype proved to be too brittle.

A rival barrier was created by Kellex, the Bell Telephone Laboratories and theBakelite Corporation from nickel powder. In January 1944,

Groves ordered the Kellex barrier into production.[112]

Kellex's design for K-25 called for a four-story 0.5 miles ¶ 800 m) long U-shaped structure containing 54 contiguous buildings. A survey

party began construction by marking out the 500acres¶ 200 ha) site in May 1943. Work on the main building began in

́ ctober

1943,and the six-stage pilot plant was ready for operation on 17 April 1944. In 1945 Groves canceled the upper stages of the plant,

directing Kellex instead to design and build 540-stage side feed unit, which became known as K-27. Kellex transferred the last unit to

the operating contractor, Union Carbide and Carbon on 11 September 1945. The total cost, including K-27 plant which was completed

after the war, came toµ 480million.[113]

The production plant commenced operation in February 1945, and as cascade after cascade came online, the quality of the product

increased. By April 1945, K-25 had attained a 1.1% enrichment and the output of the S-50 thermal diffusion plant began being used as

feed. Some nearly 7% product was produced the next month. In August, the last of the 2, 892 stages commenced operation. K-25 and

K-27 achieved their full potential the early post-war period, when they eclipsed the other production plants and became the prototypes

for a new generation of plants.[114]

[edit]Thermal diffusion

Mai ·

ar ticl ̧ : S-50 ( Manhatt an P roject)



The thermal diffusion process was developed by US ¹ avy scientists, and was not one of the enrichment technologies initially selected

for use in the Manhattan Project.º

owever, in April 1944, » ppenheimer, noting the progress of Philip Abelson's experiments onthermal

diffusion at the ¹ aval Research Laboratory, wrote to Groves suggesting that the output of a thermal diffusion plant could be fed into Y-

12. Groves set up a committee consisting of Warren K. Lewis, Eger Murphree and Richard Tolman to investigate the idea. They

estimated that a thermal diffusion plant costing¼

3.5million could enrich 50 kilograms of uranium per week to nearly 0.9% uranium-235.

Groves approved its construction on 24 June 1944.[115]

K-25 powerhouse with S-50 plant beyond it, viewed from the air.

Groves contracted with theº

.K. Ferguson Company of Cleveland, » hio, to buil d the thermal diffusion plant, which was designated S-

50.º

is advisers had estimated that it would take six months to build ; Groves gave them just four. ¹ ichols created a specialS-50 office

within the MED headquarters, headed by Lieutenant Colonel Mark C. Fox, with Major Thomas J. Evans, who would succeed Fox in

March 1945, as his deputy. Plans called for the installation of 2,142 48-foot-tall½

15 m) diffusion columns arranged in 21 racks. Inside

each column were three concentric tubes. Stream obtained from the nearby K-25 powerhouse at a pressure of 100pounds per square

inch½

690 kPa) and temperature of 545°F½

285 °C) flowed downward through the innermost 1.25inches½

32 mm) nickel pipe while water

at 155 °F½

68 °C) flowed upwards through the outermost iron pipe. Isotope separation occurred in uranium hexafluoride between the

nickel and copper pipes.[116]

Work commenced on 9 July 1944 and in September, S-50 began partial operation. Furgussen operated the plant through a subsidiary

known as Fercleve. The plant produced just 10.5pounds½

4.8 kg) of 0.852% uranium-235 in » ctober. Leaks limited production and

forced shut downs over the next months but in June 1945 it produced 12,730 pounds½

5,770 kg).[117] By March 1945, all 21 production

racks were operating. Initially the output of S-50 was fed into Y-12, but staring in March 1945all three enrichment processes were run in

series. S-50 became the first stage, enriching from 0.71% to 0.89%. This material was fed into the gaseous diffusion process in the K-

25 plant, which produced a product enriched to about 23%. This was, in turn, fed into Y-12, which boosted it to about 85%, sufficient for

nuclear weapons.[118]

[edit]Weapon design

Mai n ar ticl e: ¾ ittl e Boy



Workers load uranium slugs into the X10 Graphite Reactor

In March 1943, DuPont began construction of the plutonium semiworks on a 112acresÀ

45 ha) site at Á ak Ridge. Intended as apilot

plant for the larger production facilities atÂ

anford, it included the air cooledX-10 Graphite Reactor , a chemical separation plant, and

support facil ities. Because of the subsequent decision to const ruct water cooled reactors atÂ

anford, only the chemical separation plant

operated as a true pilot.[121] The X-10 Graphite Reactor consisted of a huge block of graphite, 24 feetÀ

7.3 m) on each side, weighing

around 1,500 tons, surrounded by 7 feetÀ

2.1 m) of high-density concrete as a radiation shield.[121] The greatest difficulty was

encountered with the uranium slugs produced by Mallinckrodtand MetalÂ

ydrides. These somehow had to be coated inaluminum to

avoid corrosion and the escape of fission products into the cooling system. The Grasselli Chemical Company attempted to develop

a hot dipping process without success. Meanwhile Alcoa tried canning. A new process for flux-less welding was developed but the

necessary reliability proved elusive. While 97% of the cans passed a standard vacuum test, high temperature tests indicated afailure

rate of more than 50%. The Metallurgical Laboratory eventually developed an improved welding technique with the help of General

Electric.[122]

Watched by Fermi and Compton, the X-10 Graphite Reactor went critical on 4Ã

ovember 1943 with about 30 tons of uranium. A week

later the load was increased to 36 tons, raising its power generation to 500KW, and by the end of the month first 500milligramsÀ

7.7 gr)

of plutonium was created.[123] Modifications over time gradually raised the power to 4,000KW in July 1944. X-10 operated as a

production plant until January 1945, when it was turned over to research activities.[124] An air cooled design was chosen for the reactor

at Á ak Ridge to facilitate rapid construction, but it was recogni Ä ed that this would be impractical for the much larger production reactors.

Initial designs by the Metallurgical Laboratory and DuPont usedhelium for cooling, but the difficulties led to investigation of alternatives.

When it was determined that a water cooled reactor would be simpler, cheaper and quicker to build, this was chosen instead.[125] The

design did not become available until 4 Á ctober 1943, so in the meantime Matthias concentratedon accommodation, improving the

roads, building a railway switch line, upgrading the electricity, water and telephone lines.[126]

Aerial view of Å

anfordB-Reactor site, June 1944

Work began on the first of three 250MW reactors, known as Reactor B, on 10 Á ctober 1943. Some390 tons of steel, 17,400cubic

yardsÀ

13,300 m3) of concrete, 50,000 concrete blocks and 71,000 concrete bricks were used to construct the 120-footÀ

37 m) high

building. Construction of the reactor itself commenced in February 1944.[127] As at Á ak Ridge, most difficulty was encountered with

canning the uranium slugs, which commenced atÂ

anford in March 1944. They werepickled to remove dirt and impurities, dipped in



molten bronÆ e, tin, andaluminum-silicon alloy, and canned using hydraulic presses and then capped usingarc welding under

an argon atmosphere. Finally, they were subjected to a series of tests to detect holes or faulty welds. Disappointingly,most canned

slugs initially failed the tests, resulting in an output of only a handful of canned slugs per day.Ç

owever steady progress was made and

by June 1944 production increased to the point where it appeared that enough canned slugs would be available to start the reactor on

schedule in August.

[128]

Watched by Compton, Matthias,Crawford Greenewalt and Fermi, who inserted the first slug, the process of powering up the reactor

commenced on 13 September 1944. È ver the next few days, 838 tubes were loaded and the reactor went critical. Shortly after midnight

on 27 September, the operators began to withdraw thecontrol rods to initiate production. At first all appeared well but around 03:00 the

power level started to drop and by 06:30 the reactor had shut down completely.The cooling water was investigated to see if there was a

leak or contamination. The next day the reactor started up again, only to shut down once more. It seemed that the reactor hada half-

life of about 9.7 hours.[129][130] Fermi contacted Chien-Shiung Wu, who identified the cause of the problem asneutron

poisoning from xenon-135.[131]Fortunately, DuPont engineer George Graves had deviated from the Metallurgical Laboratory's original

design in which the reactor had 1,500 tubes arranged in a circle, and had added an additional 504 tubes to fill in the corner s. The

scientists had originally considered thisoverengineering and a waste of time and money, but it was found that by loading all 2, 004 tubes

and carefully monitoring the power levels, the reactor could reach the required power level and efficiently produce

plutonium.[132] Reactor D was started on 17 December 1944 and Reactor F on 25 February 1945.[133]

[edit]Thin Man

T hi n Man casings. A Fat Man casing is also visible in the photo background.

In 1943, development efforts were directed to agun-type fission weapon with plutonium calledT hi n Man. Initial research on the

properties of plutonium was done usingcyclotron-generated plutonium-239, which was extremely pure, but could only be created in very

small amounts. Los Alamos received thefi rst sample of plutonium from the Clinton X-10 reactor in April 1944 and within days Emilio

Segrè discovered a problem: the reactor-bred plutonium had a higher concentration of plutonium-240, resulting in up to fi ve times the

spontaneous fission rate as cyclotron plutonium.

[134]

This made reactor plutonium unsuitable for use in a gun-type weapon. The

plutonium-240 would start the chain reaction too quickly, causing apredetonation which would release enough energy to disperse the

critical mass with a minimal amount of plutoniumreacted É a fiÊ Ê

le). A faster gun was suggested but found to be impractical. The

possibility of separating the isotopes was considered and rejected, as plutonium-240 is even harder to separate from plutonium-239

than uranium-235 from uranium-238.[135]

Work on an alternative method of bomb design, known as implosion, had begun earlier atthe instigation of the physicistSeth

Ë eddermeyer . Implosion would use chemicalexplosive lenses to inwardly crush a sub-critical sphere of fissile material into a smaller



and denser form. W hen the fissile atoms were packed closer together, the rate of neutron capture would increase, and the masswould

become a critical mass. The metal needed to travel only very short distances, so the critical mass would be assembled in much less

time than it would take with the gun method.[136] Ì eddermeyer's 1943 and early 1944 investigations into implosion showed promise, but

also made it clear that the problem would be much more difficult from a theoretical and engineering perspective than the gundesign.

But by July 1944, having concluded plutonium could not be used in a gun design,Í

ppenheimer abandoned the gun design for the

plutonium bomb, in favor of implosion.John von Ì eumann, who had experience with shaped charges used in armor-piercing shot and

shell argued that not only would implosion reduce the danger of predetonation and fiÎ Î

le, but would make more efficient use of the

fissionable material.[137] In August 1944, Í ppenheimer implemented a sweeping reorgani Î ation of the Los Alamos laborator y to focus on

implosion.[138]

[edit]Separation process

Meanwhile, the chemists considered the problem of how plutonium could be separated from uranium when its chemical propertieswere

not known. Working with the minute quantities of plutonium available at the Metallurgical Laboratory in 1942, a team under Charles M.

Cooper developed a lanthanum fluoride process for separating uranium and plutonium, which was chosen for the pil ot separationplant.

Ï owever Seaborg and Stanly G. Thomson also developed thebismuth phosphate process, and this was considered a good backup

process.[139] In May 1943, Greenewalt decided to use the bismuth phosphate process. In the event, both were used in

combination.[140] Í nce X-10 began producing plutonium, the pilot separation plant was put to the test. The first batch was processed at

40% efficiency but over the next few months this was raised to 90%.[141]

Chemical separation plant atÐ

anford

Early plans called for the construction of two separation plants in the areas known as 200-West and 200-East. This was subsequently

reduced to two, the T and U plants, in 200-West and one, the B plant at 200-East.[142] Each separation plant consisted of four buildings:

a process cell building or "canyon"Ñ

221), a concentration buildingÑ

224), a purification buildingÑ

231) and a maga Î ine storeÑ

213). The

canyons were each 800 feetÑ

240 m) long and 65 feetÑ

20 m) wide. Each consisted of forty 17.7-footÑ

5.4 m) by 13-footÑ

4.0 m) by 20-

footÑ

6.1 m) cells.[143] Work began on 221-T and 221-U in January 1944, with the form er completed in September and the latter in

December. The 221-B building followed in March 1945. Because of the high levels of radioactivity involved, all work in the separation

plants had to be conducted by remote control usingclosed-circuit television. Maintenance was carried out with the aid of anoverhead

crane and specially designed tools. The 224 buildings were smaller because they had less material to process, and it was less



radioactive. The 224-T and 224-U buildings were completed on 8 Ò

ctober 1944, and 224-B followed on 10 February 1945. Ó ow the

231-W purification plant was going to work was not known when construction comm enced on 8 April 1944, but it was completed by the

end of the year.[144] Ò

n 5 February 1945, Matthias hand delivered the first shipmentof 80 grams Ô 2.8 oÕ

) of 95% pure plutonium nitrate

to a Los Alamos courier inLos Angeles.[133]

[edit]Metallurgy

The ultimate task of the metallurgists was to figure out how to cast plutonium into a hollowsphere. The difficulties became apparent

when attempts to measure thedensity of plutonium gave inconsistent results. At first contamination was believed to be the cause but it

was soon determined that there were multipleallotropes of plutonium.[145] The brittle phase that exists at room temperature changes to

the plastic phase at highertemperatures. Attention then shifted to the even moremalleable phase that normally exists in the 300°C

to 450 °C range. It was found that this was stable at room temperature when alloyed with alum inum; but aluminum emits neutrons when

bombarded with alpha particles, which would exacerbate the pre-ignit ion problem. The metallurgists then hit uponplutonium-gallium

alloy, which stabiliÕ

ed the phase and could behot pressed into the desired spherical shape. As plutonium was found

to corrode readily, the sphere was coated with nickel.[146]

The work proved dangerous. By the end of the war, half the experienced chemists and m etallurgists had to be removed from workwith

plutonium when unacceptably high levels of the element appeared in their urine.[147] A minor fire at Los Alamos in January 1945 led to a

fear that a fire in the plutonium laboratory might contaminate the whole town, and Groves authoriÕ

ed the construction of a new facility

for plutonium chemistry and metallurgy, which became known as DP-site. [148] The hemispheres for the first plutoniumpit were produced

and delivered on 2 July 1945. Three more hemispheres followed on 23 July and were delivered three days later.[149]

[edit]Weapon design

Mai n ar ticl e:Fat Man

An implosion-type nuclear bomb

The accelerated effort on an implosion design, codenamedFat Man, began in August 1944. The explosives group was headed

by George Kistiakowsky.[150]

The design of lenses that detonated with just the right shape and velocity turned out to be slow, difficult and

frustrating.[151]Various explosives were tested before settling oncomposition B as the fast explosive andbaratol as the slow

explosive.[152] Getting the shape just right required fast, reliable and safe electricaldetonators. It was therefore decided to

use exploding-bridgewire detonators. A contract for their manufacture was given toRaytheon.[153] To study the behavior of

converging shock waves, Serber devised the RaLa Experiment, which used the short-lived radioisotope lanthanum-140, a potent source

of gamma radiation.[154]

With all the effort t o avoid predetonation, a method was required to start the chain reaction at precisely the right



moment.[155] For this a Polonium-Beryllium modulated neutron initiator was developed. Testing required up to 500 curies per month of

Polonium, which fortunately theMonsanto Company was able to deliver.[156]

[edit]Trinity

Mai n ar ticl e: T r i nit y ( nucl ear t est)

Because of the complexity of an implosion-style weapon, it was decided that, despite the waste of fissile material, an initial test would be

required. Groves approved the test, subject to the active material being recovered. Consideration was therefore given to a

controlled fi Ö Ö le but × ppenheimer soon opted instead for a full-scale explosion inside a containment vessel. This would enable the

active material to be recovered in the event of a failure, as Groves did not relish the prospect of explaining the loss of abillion dollars

worth of plutonium to asenate commi ttee.[157] × ppenheimer gave the nuclear test the code name "Trinity".[158]

The explosives of the Gadget were raised up to the top of the tower for the final assembly

In March 1944, planning for the test was assigned toKenneth Bainbridge, a professor of physics at Ø arvard, working under

Kistiakowsky. Bainbridge selected the Alamogordo Bombing Rangenear Alamogordo Army Airfieldas the site for the

test.[159]

Bainbridge worked with Captain Samuel P. Davalos on the construction of the Trinity Base Camp and its facilities, which

included barracks, warehouses, workshops, an explosive magaÖ

ine and a commissary.[160]

The cylindrical containm ent vessel, code-named "Jumbo", m easuring 25 feetÙ 7.6 m) long and 12 feet

Ù 3.7 m) wide, was fabricated at

great expense from 214 tons of iron and steel byBabcock & Wilcox in Barberton, × hio. It was duly brought in a special railroad car to

a siding in Pope, Ú ew Mexico and was transported the last 25miles Ù 40 km) from there to the test site on a trailer pulled bytwo tractors.

By the time it arrived confidence in the implosion method was high enough and the availability of plutonium was sufficient enough that

× ppenheimer decided not to use it. Instead, it was hoisted up in a steel tower 800yards Ù 730 m) from the gadget as a rough measure of

how powerful the explosion would be. In the end, "Jumbo" survived, though its tower did not, adding credence to the widespread belief

that Jumbo would have successfully contained a fiÖ Ö

led explosion.[161][162]

A pre-test explosion was conducted on 7 May 1945 to calibrate the instruments. A wooden test platf orm was erected 800 yards Ù 730 m)

from Ground Zero and piled with 100 tons of T Ú T, spiked withnuclear fission products in the form of a molten irradiated uranium slug

from Ø anford. The test was observed by × ppenheimer and Groves' new deputy commander, Brigadier GeneralThomas Farrell. It

served as a dress rehearsal for the main test. While most of the experiments conducted were of slight value, important lessons were

learned concerning the mundane but vital aspects of conducting a test.[162][163]



For the actual test, the device, nicknamedt he gadget , was hoisted to the top of a 100-foot-high steel tower Û

30 m) for detonation, since

this would give a better indication of how the weapon would behave when dropped from a bomber. Detonation in the air maximi Ü ed the

energy applied directly to the target, and generated lessnuclear fallout. The gadget was assembled under the supervision of Ý

orris

Bradbury at the nearby McDonald Ranch Þ ouse on 13 July, and precariously winched up the tower the following day.[164]

ß bservers

included Bush, Chadwick, Conant, Farrell, Fermi, Groves, Lawrence,ß

ppenheimer and Tolman. At 05:30 on 16 July 1945 the gadget

exploded with an energy equivalent of around 20 kilotons of TÝ

T, leaving a crater of radioactive glass in the desert 250 feetÛ

76 m) wide

and 6 feetÛ

1.8 m) deep. The shock wave was felt over 100milesÛ

160 km) away, and the mushroom cloud reached 7.5 milesÛ

12.1 km)

in height. It was heard as far away asEl Paso, Texas, so Groves issued a cover s tory about an ammunition magaÜ ine explosion at

Alamogordo Field.[165][166]

[edit]Foreign Intelligence

Mai n ar ticl e: Operati on Al sos

The Manhattan Project was charged with gathering intelligence on theGerman nuclear energy project. It was believed that

the Japanese atomic program was not far advanced because Japan had little access to uranium ore, but it was initially feared that

Germany was very close to developing its own weapons. At the instigation of the Manhattan Project, abombing and sabotage campaign

was carried out against heavy water plants in German-occupiedÝ

orway.[167]

A small m ission was created, jointly staffed byß ffice of

Ý

aval Intelligence, ß SRD, the Manhattan Project and Army IntelligenceÛ

G-2), to investigate enemy scienti fic developments. It was not

restricted to those involving nuclear weapons.[168]

The Chief of Army Intelligence, Major GeneralGeorge V. Strong, appointed

Lieutenant Colonel Boris T. Pash to command the unit,[169] which was codename "Alsos", a Greek word meaning "grove".[170] As head of

the Counter Intelligence Branch of the Western Defense Command, Pash had investigated suspectedSoviet espionage at the Radiation

Laboratory in Berkeley.[171]

The German experimentalnuclear reactor atà

aigerloch

The Alsos Mission to Italy questioned staff of the physics laboratory at theUniversity of Rome following the capture of the city in June

1944.[172]Meanwhile Pash formed a second Alsos Mission in London under the command of Captain Þ orace K. Calvert to participate

in ß peration ß verlord. This mission was to be a combined British and American one.[173] Groves considered the risk that the Germans

might attempt to disrupt theÝ

ormandy landings with radioactive poisons was sufficient to warn GeneralDwight D. Eisenhower and send



an officer to brief his chief of staff, Lieutenant General Walter Bedell Smith.[174] Under the code-nameá

peration Peppermint, special

equipment was prepared andChemical Warfare Service teams were trained in its use.[175]

Following in the wake of the advancing Allied armies, Pash and Calvert foundFrédéric Joliot-Curie at his laboratory at the College de

France and interviewed him about the activities of German scientists. They spoke to officials atUnion Minière du â aut Katangaand

learned about shipments of uranium ore to Germany. They tracked down some 68 tons of ore inBelgium and 30 in France. The

interrogation of German prisoners indicated that uranium and thorium were being processed iná

ranienburg, so Groves arranged for it

to be bombed on 15 March 1945.[176]

An Alsos team under Major John Lansdale, Jr went toStassfurt in the Sovietá

ccupation Zone and

retrieved 11 tons of ore fromWIFá

.[177] In April 1945, Pash, in command of a composite force known as T-Force, carried outá

peration

â arborage, a sweep of the cities of

â echingen, Bisingen and

â aigerloch that were the heart of the German nuclear effort. T Force

captured the nuclear laboratories, documents, equipment and supplies, including heavy water and 1.5 tons of m etallic uranium.[178]

Alsos teams rounded up German scientists includingKurt Diebner ,á

tto â ahn, Walther Gerlach, Werner â eisenberg and Carl Friedrich

von Weiã

säcker . They were taken to England where they were interned atFarm â all, a bugged house in Godmanchester . After the

bombs were detonated in Japan, â eisenberg, by thenimprisoned in Britain at Farm â all with several other nuclear project physicists,

almost immediately figured out what the Allies had done, explaining it to his fellow scientistsä

and the hidden microphones)within

days.[179]

[edit]Bombing of iroshima and agasaki

Mai n ar ticl e: At omic bombi ngs of Hi roshi ma and N agasak i

[edit]Preparations

Groves met with the Chief of United States Army Air Forces å USAAF), Generalæ

enryæ

. Arnold, in March 1944 to discuss the delivery

of the finished bombs to their targets.[180] The only Allied aircraft capable of carrying 17-foot å 5.2 m) long Thin Man orthe 59-inch å 150

cm) wide Fat Manwas the British Avro Lancaster , but using a British aircraft would have caused difficulties with maintenance. Groves

hoped that the American Boeing B-29 Superfortress could be modified to carryT hi n Man by joining its two bomb

bays together.[181] Arnold promised that no effort would be spared to modify B-29s to do the job.ç

e designated Major General è liver P.

Echols as the USAAF liaison to the Manhattan Project.[180] Starting in é ovember 1943, the Army Air Forces Materiel

Command at Wright Field, è hio began Silverplate, the modif ication of B-29s to carry the bombs. Test drops were carried out atMuroc

Army Air Field, California.[182]



Silverplate B-29 Straight Flush. Note lack of gun turrets. The tail code of the 444th Bombardment ê roup is painted on f or secur ity reasons.

The 509th ë omposite ì roup was activated on 17 December 1944 at Wendover Army Air Field, Utah, under the command of

ë olonel Paul W. Tibbets. The base close to the border with Nevada was codenamed "Kingman" or "W-47". Training was conducted at

Wendover and at Batista Army Air field, ë uba, where the 393d Bombardment Squadron practiced long distance flights over water . A

special unit known as Alber ta was f ormed at Los Alamos under ë aptain William S. Parsons as par t of the Manhattan Pro ject to assist in

prepar ing and deliver ing the bombs. [183]ë ommander Freder ick L. Ashwor th f rom Alber ta met with Fleet Admiral ë hester W.

Nimitz on ì uam in February 1945 to inf orm him of the pro ject. Wh ile he was there, Ashwor th selected Nor th Field on Tinian as a base

f or the 509th ë omposite ì roup, and reserved space f or the group and its buildings. The group deployed there in í uly 1945. [184] Farrell

arr ived on Tinian on the 30th of í uly as the Manhattan Pro ject representative. [185]

Most of the components f or Little Boy left San Francisco on the cruiser USS Indianaî

olis on 16 í uly and arr ived on Tinian on 26 í uly.

Four days later the ship was sunk by a í apanese submar ine. The remaining components, which included some uranium 235, were

delivered by three ë -54aircraft of the Air Transpor t ë ommand.[186] Two Fat Man assemblies travelled to Tinian in two specially modified

509th ë omposite

ì roup B-29s. The first plutonium core went in a specialë -54.[187] A joint Manhattan Distr ict-USAAF targeting

committee was established to determine which cities in í apan should be targets, which

recommended Kokura, Hiroshima, Niigata and Kyoto. At this point, Secretary of War Henry L. Stimson intervened, announcing that he

would be making the targeting decis ion, and that he would not author ize the bombing of Kyoto on the grounds of its histor ical and

religious significance (of which he had personal exper ience, having spent his honeymoon there). ì roves attempted to get him t o change

his mind several times and Stimson ref used each time. In the end, ì roves asked Arnold to remove Kyoto not just f rom the list of nuclear

targets, but f rom targets f or conventional bombing as well. [188] One of Kyoto's substitutes as a target became Nagasaki.[189]

[edit]The ï

ð

e of the bombs

Harry S. Truman was not inf ormed of the purpose of the Manhattan Pro ject until he became President of the United States after the

death of

ñ

oosevelt on 12 Apr il 1945, at which time he continued the program along the lines it had already been running. Wh il e in

Europe f or the Potsdam ò onf erence, Truman was told that the Tr inity test had been successf ul. Accordingly, he made an oblique

ref erence to the existence of a new weapon to Soviet le ader ó

oseph Stalin, who, in some accounts, appeared disinterested. This was

the first time that the US had officially notified the Soviet Union in any way about the bomb (though it did not mention its atomic nature),

though in f act, Stalin had known of the bomb longer than Truman due to successf ul espionage on the work at Los Alamos. [190] The

author ization to use the bomb againstó

apan had been given in ó

uly 1945; the ó

apanese re jection of the Potsdam Declaration insured

that no change would be made to the directive. [191]

On 6 August 1945, 393d Bombardment Squadron B -29 E nola ô ay , piloted and commanded by Tibbets lifted off f rom Nor th Field at

02:45 Tinian time, with Parsons on board as weaponeer , and with the Little Boy weapon in its bomb bay. Hiroshima, an impor tant army

depot and por t of embarkation, was the pr imary target of the mission, with Kokura and Nagasaki as alternative targets. With Farrell 's

permission, Parsons completed the bomb assembly in the air to minimize the r isks dur ing takeoff. At 08:09 Tibbets star ted his bomb run

and handed control over to his bombardier , Ma jor Thomas Ferebee. The bomb was released f rom 31,600 f eet (9,600 m) shor tly after

09:15 and the aircraft made a 150° bank to maximize the distance between itself and the blast. [192] The blast was later estimated to be

the equivalent of 13 kilotons of TNT (54 TJ).[193] Approximately 4.7 square miles (12 km

2) of the city were destroyed. Japanese officials

determined that 69% of Hiroshima's buildings were destroyed and another 6±7% damaged. About 70,000 to 80,000 people, or some

30% of the population of Hiroshima, were killed immediately, and another 70,000 in jured. [194]



Fat Man explodes over õ

agasaki, Japan, August 9, 1945.

ö n the morning of 9 August 1945, the B-29 Boc ksc ar , piloted by the 393d Bombardment Squadron's commander, Major Charles W.

Sweeney, lifted off with aFat Man on board. This time, Ashworth served as weaponeer and Kokura was the primary target. Sweeney

took off with his weapon already armed but with the electrical safety plugs still engaged. When they reached Kokura, they found cloud

cover had obscured the city, prohibiting the visual attack required by orders. After three runs over the city, and with fuel running low

because a transfer pump on a reserve tank had failed before take-off, they headed for the secondary target,÷

agasaki. Fuel

consumption calculations made en route indicated thatBoc ksc ar would be forced to divert toö

kinawa. Ashworth decided that a radar

approach would be used if the target was obscured. A last minute break in theclouds over ÷ agasaki allowedBoc ksc ar' s bombardier,

Captain Kermit Beahan, to visually sight the target as ordered. TheFat Manwas dropped from 29,000 feetø

8,800 m) over the city's

industrial valley midway between the Mitsubishi Steel and Arms Works in the south and the Mitsubishi-Urakami ö rdnance Works in the

north. The blast was confined to theUrakami Valley and a major portion of the city was protected by the intervening hills. The resulting

explosion had a blast yield equivalent to 21kilotons of T ÷ Tø

88 TJ), roughly the same as the Trinity blast. About 44% of the city was

destroyed; 35,000 people were killed and 60,000 injured.[195][196]

Groves expected to have another atomic bomb ready for use on 19 August, with three more in September and a further three in

ö ctober.[197] Two more Fat Manassemblies were readied. When the Japanese initiatedsurrender negotiations, Groves ordered the

shipments suspended. The third core was scheduled to leaveKirtland Field for Tinian on 12 August.[196] Robert Bacher was packaging it

at the Ice ù ouse at Los Alamos when he received the word.[198] ö n 11 August, Groves phoned Warren with orders to organi ú e a survey

team to report on the damage and radioactivity atù

iroshima and÷

agasaki. A party equipped with portablegeiger counters arrived in

ù iroshima on 8 September headed by Farrell and Warren, with Japanese Rear Admiral Masao Tsu ú uki, who acted as a translator. They

remained in ù iroshima until 14 September and then surveyed ÷ agasaki from 19 September to 8 ö ctober.[199]

[edit]Post-War

In anticipation of the bombings, Groves had ù enry DeWolf Smyth prepare a history for public consumption. At omic E nergy for M ilit ary

P ur poses ø

better known as the "Smyth Report") was released to the public on 12 August 1945.[200] Groves and ÷ ichols presented Army-

÷ avy "E" Awards to key contractors, whose involvement had hitherto been secret. ö ver twenty awards of thePresidential Medal for

Merit were made to key contractors and scientists, including Bush and ö ppenheimer. Military personnel received theLegion of Merit,

including the commander of the WAC detachment, Captain Arlene G. Scheidenhelm.[201]



Nichols recommended that S-50 and the Alpha tracks at Y-12 be closed down. This was done in September.[202] Although performing

better than ever,[203]

the Alpha t racks could not compete with K-25 and the new K-27, which had commenced operation in January 1946.

In December, the Y-12 plant was closed, thereby cutting the Tennessee Eastman payroll from 8,600 to 1,500 and saving û 2milli on a

month.[204]

Presidentü

arry S Truman signs the Atomic Energy Act of 1946 establishing the United States Atomic Energy Commission

At ý anford, plutonium production fell off as Reactors B, D and F wor e out, "poisoned" by fission products and swelling of the graphite

moderator known as the Wigner effect. The swelling damaged the charging tubes where the uranium was irradiated to produce

plutonium, rendering them unusable. In order to maintain the supply of polonium for the urchin initiators, the oldest unit, Bpile, was

closed down. Research continued, with DuPont and the Metallurgical Laboratory developing aRedox solvent extraction process as an

alternative plutonium extraction technique to thebismuth phosphate process, which left unspent uranium in a state from which it could

not easily be recovered.[205]

Bomb engineering was carried out by the Z Division, named for its director, Dr.Jerrold R. Zacharias from Los Alamos. Z Division was

initially located at Wendover Field but moved toþ

xnard Field, New Mexico in September 1945 to be closer toLos Alamos. This marked

the beginning of Sandia Base. Nearby Kirtland Field was used as a B-29 base for aircraft com patibilit y and drop tests.[206]

Byþ

ctober,

all the staff and facilities at Wendover had been transferred to Sandia.[207] As reservist officers were demobili ÿ ed, they were replaced by

about fifty hand-picked regular officers.[208]

Nowhere was this more of a problem than at Los Alamos, where there was an exodus of talent. Much remained to be done. The bombs

used on ý iroshima and Nagasaki were like laboratory pieces; work would be required to make them simpler, safer and more reliable.

There was also a long list of technological improvements, such as applying implosion to uranium in place of the wasteful gun method,

and using a composite uranium-plutonium core, now that plutonium was in short supply due to the problems with the reactors. ý owever,

uncertainty about the future of the laboratory made it hard to induce them to stay.þ

ppenheimer returned to his job at the University of

California and Groves appointed Norris Bradbury as an interim replacement. In the event, Bradbury world remain in the post for the next

25 years. [209] Groves attempted to combat the dissatisfaction caused by the lack of amenities with a construction program that included

an improved water supply, three hundred houses, and recreation facil ities.[205]



The war time Manhattan Pro ject left a legacy in the f orm of the network of national laborator ies: the Lawrence Berkeley National

Laboratory, Los Alamos National Laboratory, Oak

idge National Laboratory, Argonne National Laboratory and Ames Laboratory. Two

more were established by the ¡

roves soon after the war , the Brookhaven National Laboratory at Upton, New York and the Sandia

National Laborator ies at Albuquerque, New Mexico.¡ roves allocated $72 million to them f or research activities in fiscal year 1946±

1947.

[210]

A ser ies of nuclear weapon tests were conducted at Bikini Atoll in July 1946 as par t of Operation

¢

rossroads f or the purpose

of investigating the eff ect of nuclear weapons on warships. [211] The ser ies consisted of two Fat Man detonations. A£

le was detonated on

1 July 1946. The more spectacular Baker was detonated underwater on 25 July 1946. [212]

The United States Atomic Energy ¢

ommission (AE¢

) was created by the Atomic Energy Act of 1946 to take over the f unctions and

assets of the Manhattan Pro ject. It established civilian control over atomic development, and separated the development, prod uction

and control of atomic weapons f rom the military. Military aspects were taken over by the Armed Forces Special Weapons

Pro ject(AFSWP).[213]

[edit] ost of the Manhattan Pro ject

The pro ject expenditure to 1 October 1945 was $1.845 billion, and was

$2.191 billion when the AE¢

assumed control on 1 January 1947. Total

allocation was $2.4 billion, an amount equal to $23.6 billion in current

value. Over 90% of the cost was f or building plants and producing the

fissionable mater ials, and less than 10% f or development and production

of the weapons.[215]

A total of four weapons ¤ the Tr inity gadget, Little Boy , Fat Man, and one more unused weapon) were pr oduced by the end of

1945, making the average cost per bomb ar ound $500 million in 1945 dollars ¤ $6 billion in current USD). ¥ y compar ison, the

total pr ice by the end of 1945 was about 60% of the total cost spent on all other bombs, mines, and grenades pr oduced; 80%

of all small ar ms mater iel ¤

not including ammunition); and 31% of the cost of all tanks pr oduced, all dur ing the same time

per iod.[214] Attack on Pear l Harbor

From W ikipedia, the f ree encyclopedia

T his arti ¦

le is a§

out the histori ¦

event. For the video game, see Atta¦

k on Pearl ̈

ar §

or ©

video game

.

Attack on Pearl Harbor

Part of the Pacific Theater of World War II

Costs of the Manhattan Project through 31 December 1945[214]

Site Cost (1945 USD)

Oak Ridge $1,188,352,000

Hanford $390,124,000

Special Operating Mater ials $103,369,000

Los Alamos $74,055,000

R esearch and Development $69,681,000

Government Overhead $37,255,000

Heavy Water Plants $26,768,000

Total $1,889,604,000



Photograph from a Japanese plane of Battleship Row at the beginning of the attack.

The explosion in the center is a torpe o strike on theUSS Oklahoma. Two attacking

Japanese planes can be seen: one over the USS Neosho and one over the Naval Yard.

Dat

December 7, 1941

Lo

ation PrimarilyPearl Harbor, Hawaii Territory,

United States

R

sult Japanesemajor tactical victory

United States declares war on the

Empire of Japan

Nazi Germany and Fascist Italy declare

war on the United States.

Belligerents

United States of America Empire of Japan

Commanders andleaders

Husband Kimmel

Walter Short

Chuichi Nagumo

Isoroku Yamamoto

Strength

8 battleships,8 cruisers,

30 destroyers,

4 submarines,

49 other ships,[1]

~390 aircraft

Mobile U

nit: 6 aircraft carriers,

2 battleships,

2 heavycruisers,

1 light cruiser,

9 destroyers,

8 tankers,

23 fleet submarines,

5 midget submarines,

414 aircraft



Casualties and losses

4 battleships sun

,

4 battleships damaged including 1 run

aground

2 destroyers sun

, 1 damaged

1 other ship sun

, 3 damaged

3 cruisers damaged [nb 1]

188 aircraft destroyed

155 aircraft damaged,

2,402 military illed

1,247 military wounded

57 civilians

illed

35 civilians wounded[3][4]

4 midget submarines sun

,

1 midget submarine run aground,

29 aircraft destroyed,

55 airmen

illed

9 submariners

illed

1 submariner captured [5]

[show]v · d · e

Hawaiian Islands Ca

pai

n

[show]v · d · e

Pacific Ca

pai

ns 194042

[show]v · d · e

Pacific Ocean theater

The attack on Pear l Harbor (called Hawaii Operation or Operation Z by the Japanese Imper ial

eneral Headquar ters[6]

and the

attle of Pear l

Harbor [7]

) was a surpr ise military str ike conducted by the Imper ial Japanese Navy against the United States naval base at Pear l Harbor , Hawaii,

on the morning of December 7, 1941 (December 8 in Japan). The attack was inten ded as a preventive action in order to keep the U.S. Pacific

Fleet f rom inter f er ing with military actions the Empire of Japan was planning in Southeast Asia against overseas terr itor ies of the United Kingdom,

the Nether lands, and the United States.

The base was attacked by 353 Japanese aircraft in two waves, launched f rom six aircraft carr iers.[8]

Four U.S. Navy battleships were sunk (two of

which were raised and returned to service later in the war) and the f our others present were damag ed. The Japanese also sank or damaged

threecruisers, three destroyers, an anti-aircraft training ship,[9]

and oneminelayer . 188 U.S. aircraft were destroyed; 2,402 men were killed[10]

and

1,282 wounded. The power station, shipyard, maintenance, and f uel and torpedo storage f acilities, as well as the submar ine pi ers and

headquar ters building (also home of the intelligence section) were not attacked. Japanese losses were light: 29 aircraft and five midget

submar ines lost, and 65 servicemen killed or wounded. One Japanese sailor was captured.

The attack came as a prof ound shock to the Amer ican people and led directly to the Am er ican entry into Wor ld War II in both

the Pacific andEuropean theaters. The f ollowing day (December 8) the United States declared war on Japan. Domestic suppor t f or isolationism,

which had been strong, disappeared. landestine suppor t of Br itain (f or examp le the Neutrality Patrol) was replaced by active alliance.

Subsequent operations by the U.S. prompted

ermany and Italy to declare war on the U.S. on December 11, which was reciprocated by the U.S.

the same day.

Despite numerous histor ical precedents f or unannounced military action, the lack of any f ormal warning by Japan, par ticular ly while negotiations

were still apparently ongoing, led President Franklin D. oosevelt to proclaim December 7, 1941, "a date which will live in inf amy".

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