During World War II Alan Turing worked for the Government at Bletchley Park, the estate housed the Government Code and Cypher School (GC&CS), which regularly penetrated the secret communications of the Axis Powers – most importantly the German Enigma and Lorenz ciphers. The GC&CS team of codebreakers also included Gordon Welchman, Hugh Alexander, Bill Tutte, and Stuart Milner-Barry. The nature of the work at Bletchley remained secret until many years after the war.

According to the official historian of British Intelligence, the "Ultra" intelligence produced at Bletchley shortened the war by two to four years, and without it the outcome of the war would have been uncertain. The team at Bletchley Park devised automatic machinery to help with decryption, culminating in the development of Colossus, the world's first programmable digital electronic computer. Codebreaking operations at Bletchley Park came to an end in 1946 and all information about the wartime operations was classified until the mid-1970s.

Work After the war

After the war Turing joined the National Physical Laboratory (NPL) in October 1945, by which time scientists within the Ministry of Supply had concluded that Britain needed a National Mathematical Laboratory to co-ordinate machine-aided computation. A Mathematics Division was set up at the NPL, and on 19 February 1946 Alan Turing presented a paper outlining his design for an electronic stored-program computer to be known as the Automatic Computing Engine (ACE).

This was one of several projects set up in the years following the Second World War with the aim of constructing a stored-program computer. At about the same time, EDVAC was under development at the University of Pennsylvania's Moore School of Electrical Engineering, and the University of Cambridge Mathematical Laboratory was working on EDSAC.

The Automatic Computing Engine (ACE) was a British early electronic serial stored-program computer design by Alan Turing. Turing completed the ambitious design in late 1945, having had experience in the years prior with the secret Colossus computer at Bletchley Park.

The ACE was not built, but a smaller version, the Pilot ACE, was constructed at the National Physical Laboratory and became operational in 1950. A larger implementation of the ACE design was the MOSAIC computer which became operational in 1955. ACE also led to the Bendix G-15 and other computers.

Turing's colleagues at the NPL, not knowing about Colossus, thought that the engineering work to build a complete ACE was too ambitious, so the first version of the ACE that was built was the Pilot Model ACE, a smaller version of Turing's original design. Turing's assistant, Jim Wilkinson, worked on the logical design of the ACE and after Turing left for Cambridge in 1947, Wilkinson was appointed to lead the ACE group. The Pilot ACE had fewer than 1000 thermionic valves (vacuum tubes) compared to about 18,000 in the ENIAC. It used mercury delay lines for its main memory. Each of the 12 delay lines was 5 feet (1.5 m) long and propagated 32 instructions or data words of 32 bits each. This ran its first program on 10 May 1950, at which time it was the fastest computer in the world; each of its delay lines had a throughput of 1 Mbit/s.

The first production versions of the Pilot ACE, the English Electric DEUCE, of which 31 were sold, were delivered in 1955.

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In the Public Domain

Manchester University SSEM 'Baby' replica on display at the Museum of Science and Industry in Manchester.

Pilot Ace