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Colossus Developed by a Secret English Team, c. 1940-c. 1945

Table of Contents:Further Readings

A secret team of specialists developed Colossus, the first all-electronic calculating device, in

response to the need to decipher German military codes duringWorldWarII

Principal Personages

Thomas H. Flowers, the electronics expert who led the team that designed and built the Colossus

and who was a major proponent for the use of vacuum tubes in computers

Max H. A. Newman (1897- ), a gifted mathematician and lecturer who was responsible for

formulating the requirements for Colossus

Alan Turing (1912-1954), a brilliant mathematician who contributed to the codebreaking

computers that were the forerunners of Colossus

C. E. Wynn-Williams, a member of the Telecommunications Research Establishment who

worked on the electronic components of Colossus

Summary of Event

In 1939, during WorldWarII, a team of scientists, mathematicians, and engineers met at

Bletchley Park, outside London to discuss the development of machines that would break the

secret code used in Nazi military communications. The Germans were using a machine called

"Enigma" to communicate in code between headquarters and field units. The Enigma used a

substitution code whereby a set of letters were substituted for the ones that normally made up the

words. This in itself was not new; however, the Enigma enciphered (coded) only one letter and

then shifted to a new position so that each letter of every word had a different key. The senders

and receivers of the codes knew which rotor was being used for the substitution. The machine-

made code used several rotors and so had vast substitution possibilities, which made the code

extremely difficult to decode. The Enigma was portable, easy-to-use, and seemingly generated

unbreakable codes. Polish scientists, however, had had been able to examine a German Enigmaand were able to break the codes from 1928 to 1938 by using electromechanical codebreaking

machines called "bombas." In 1938, the Germans made the Enigma more complicated, and the

Polish were no longer able to break the codes. In 1939, the Polish machines and codebreaking

knowledge passed to the British.

Alan Mathison Turing was one of the mathematicians gathered at Bletchley Park to work on

codebreaking machines. Turing was one of the first people to conceive of the universality of

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digital computers. He first mentioned the "Turing machine" in 1936 in an article published in

"Proceedings," a publication of the London Mathematical Society. The Turing machine is a

hypothetical device for solving any problem dependent on mathematical computation and is not

restricted to only one task, hence, the universality feature. Turing's original and innovative

contributions made him essential to the team working on codebreaking machines. Turing

suggested an improvement to the Bletchley codebreaking machine, the "Bombe," which had

been modeled on the Polish "bomba." This improvement increased the computing power of the

machine. The Bombe was an electromechanical relay machine that was similar to the Enigma.

The Bombe did not decode messages itself, but worked out the position of the Enigma rotors.

Once the position of the Enigma rotors was known, the message could be decoded by specialists.

The codebreaking machines replaced the tedious method of decoding by hand, which in addition

to being slow, was ineffective in dealing with very complicated encryptions that were changed

daily.

The Bombe was very useful until 1942, when the Germans started using a more sophisticated

cipher machine known as the "Fish." The Fish used a binary code (a system of numbers in base

two, in which the only numerals are 0 and 1). Max H. A. Newman, who was in charge of one

subunit at Bletchley Park, believed that an automated device could be designed to break the

codes produced by the Fish. Thomas H. Flowers, who was in charge of a switching group at the

Post Office Research Station at Dollis Hill, had been approached to build a special purpose

electromechanical device for Bletchley Park in 1941. The device was not useful, and Flowers

was assigned to other problems. He worked closely with Turing, Newman, and C. E. Wynn-

Williams of the Telecommunications Research Establishment (TRE) to develop a machine to

break the Fish codes. The Dollis Hill team worked on the tape driving and reading problems, and

Wynn-Williams' team at TRE worked on electronic counters and the necessary circuitry. Theirefforts produced the Heath Robinson, which could read two thousand characters per second. The

Heath Robinson used vacuum tubes, an uncommon component in the early 1940's. The vacuum

tubes performed more reliably and rapidly than the relays that had been used for counters. Heath

Robinson and the companion machines proved that high-speed electronic devices could

successfully do cryptoanalytic work (solve decoding problems). Entirely automatic in operation

once started, the Heath Robinson was put together at Bletchley Park in the spring of 1943. The

Heath Robinson machine had a small total output because of problems with reliability and, when

the machine overheated, it was known to seize up and catch fire. The team working on the

problems finally solved them and was able to use the machine in codebreaking. The Heath

Robinson was inadequate for the codebreaking needs shortly after it was put into use, so workbegan on a bigger, faster, and more powerful machine: the Colossus.

Flowers led the team that designed and built the Colossus in eleven months at Dollis Hill. The

first Colossus (Mark I) was a bigger, faster version of the Heath Robinson and read about five

thousand characters per second. Colossus had approximately 1,500 vacuum tubes, which was

more than any tried elsewhere at the time. Although Turing and Wynn-Williams were not

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directly involved with the design of the Colossus, their previous work on the Heath Robinson

was crucial, since the first Colossus was based on the Heath Robinson.

Colossus was operational at Bletchley Park in December, 1943, and Flowers made arrangements

for the manufacture of the time-consuming components in case other machines were required.

The request for additional machines came in March, 1944. The second Colossus, the MarkII,was extensively redesigned and was able to read twenty-five thousand characters per second

because it was capable of parallel operations (it carried out several different operations at once,

instead of one at a time) and, in addition, it had a short-term memory. The MarkII was in

operation on June 1, 1944. Several more machines were made, each with further modifications,

for a total of ten. The Colossus machines were special-purpose, program-controlled electronic

digital computers, the only known electronic programmable computer in existence in 1944. The

use of electronics allowed for a tremendous increase in the internal speed of the machine.

AfterWorldWarII ended in 1945, the Bletchley team disbanded. The fates of the Colossus,

Heath Robinson, and Bombe machines were not known for certain, since the British governmentconsidered the codebreaking work at Bletchley Park a state secret. Approximately ten thousand

men and women who worked there were sworn to secrecy and worked under the "need to know"

rule. (A person was told only the information needed to complete an assigned task.) The

commitment to secrecy was so effective that no one outside the project knew about the

codebreaking work at Bletchley Park for more than thirty years afterWorldWarII ended. The

British government officially revealed some information on the work and the people involved in

1975, but the rest of the information is still considered a state secret.

Impact of Event

The full impact of the development of the Colossus is difficult to assess accurately because all

the information about the project has not been revealed. The Colossus machines gave Britain the

best codebreakers during WorldWarII and provided information that was crucial for the Allied

victory. The information decoded by Colossus, the actual messages, and their influence on

military decisions still remains classified.

The later work of several of the people involved with the Bletchley Park projects was important

in British computer development after the war. Newman's and Turing's postwar careers were

closely involved with emerging computer advances. Newman went to Manchester Universityshortly after the war. He was interested in the impact of computers on mathematics and received

a grant from the Royal Society in 1946 to establish a calculating machine laboratory at

Manchester. He was also involved with postwar computer growth in Britain. Several other

members of the Bletchley Park team joined Newman at Manchester, including Turing in 1948.

Before going to Manchester University, however, Turing joined Britain's National Physical

Laboratory (NPL). At NPL, Turing worked on an advanced computer known as the Pilot

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Automatic Computing Engine (Pilot ACE). While at NPL, Turing proposed the concept of a

stored program, which was a controversial but extremely important idea in computing. A

"stored" program is in residence inside the computer and then a particular program and data are

fed through an input device simultaneously. (The Heath Robinson and Colossus machines were

limited by utilizing separate input tapes, one for the program and one for the data to be analyzed.

) Turing was among the first to explain the stored program concept in print. He was also among

the first to imagine how subroutines could be included in a program. (A subroutine allows

separate tasks within a large program to be done in distinct modules, a directed detour within a

program. After the completion of the subroutine, the main program takes control again.) Turing

also contributed to the computer output facilities, worked on the art of programming, and wrote

the first Manchester programming manual.

Some of the people who were involved in the Colossus project and its predecessors contributed

to Britain's postwar computer development. DuringWorldWarII, the codebreaking work at

Bletchley Park enabled Allied forces to make informed, decisive moves that eventually resulted

in Allied victory. The full story of the Colossus and the people at Bletchley Park will not be

known, however, until the British government declassifies the information.