- Alan Turing Part 2 -

Alan Turing, his life
and 'The Imitation Game' - Part 2

Please click here to go to Part 1

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Turing's machine that helped decode Enigma was the electromechanical Bombe (described on the previous page), not Colossus.

Colossus was designed by the engineer Tommy Flowers to solve a problem posed by mathematician Max Newman at Bletchley Park.

Colossus, the first large-scale electronic computer, was used against the German system of teleprinter encryption known at Bletchley Park as 'Tunny'. Technologically more sophisticated than Enigma, Tunny carried the highest grade of intelligence.

From 1941 Hitler and the German High Command relied increasingly on Tunny to protect their communications with Army Group commanders across Europe.

Tunny messages sent by radio were first intercepted by the British in June 1941. After a year-long struggle with the new cipher, Bletchley Park first read current Tunny traffic in July 1942. Tunny decrypts contained intelligence that changed the course of the war in Europe, saving an incalculable number of lives.

The Tunny machine was manufactured by the German Lorenz company. The first model bore the designation SZ40, SZ standing for 'Schlüsselzusatz' ('cipher attachment'). A later version, the SZ42A, was introduced in February 1943, followed by the SZ42B in June 1944.

Turing briefly joined the attack on Tunny in 1942, contributing a fundamentally important cryptanalytical method known simply as 'Turingery'.


Colossus was the world's first electronic digital computer that was programmable.

The Colossus computers were developed for British codebreakers during World War II to help in the cryptanalysis of the Lorenz cipher.

Without them, the Allies would have been deprived of the very valuable military intelligence that was obtained from reading the vast quantity of encrypted high-level telegraphic messages between the German High Command (OKW) and their army commands throughout occupied Europe.

Colossus used thermionic valves (vacuum tubes) to perform Boolean operations and calculations.

It has sometimes been erroneously stated that Turing designed Colossus to aid the cryptanalysis of the Enigma. However Alan Turing's use of probability in cryptanalysis did contribute to its design.

For more details about Colossus and Bletchley Park please click on the link at the top of this page.

Colossus in use during the war (above).

Colossus under reconstruction 2003.


The Pilot Automatic Computing Engine (ACE), pictured below, was an early electronic stored-program computer design produced by Alan Turing at the invitation of John R. Womersley, superintendent of the Mathematics Division of the National Physical Laboratory (NPL).

The use of the word Engine was in homage to Charles Babbage and his Difference Engine and Analytical Engine. Turing's technical design, 'Proposed Electronic Calculator', was the product of his theoretical work in 1936, "On Computable Numbers" mentioned on the previous page, and his wartime experience at Bletchley Park where the Colossus computers had been successful in breaking German military codes.

In his 1936 paper, Turing described his idea as a "universal computing machine", but it is now known as the "Universal Turing machine".

On 19 February 1946 Turing presented a detailed paper to the National Physical Laboratory (NPL) Executive Committee, giving the first reasonably complete design of a stored-program computer. However, because of the strict and long-lasting secrecy around the Bletchley Park work, he was prohibited (because of the Official Secrets Act) from explaining that he knew that his ideas could be implemented in an electronic device.

The better-known EDVAC design presented in the First Draft of a Report on the EDVAC (dated June 30, 1945), by John von Neumann, who knew of Turing's theoretical work, received much publicity, despite its incomplete nature and questionable lack of attribution of the sources of some of the ideas.

Turing's report on the ACE was written in late 1945 and included detailed logical circuit diagrams.

The ACE implemented subroutine calls, whereas the EDVAC did not, and what also set the ACE apart from the EDVAC was the use of Abbreviated Computer Instructions, an early form of programming language.

Initially, it was planned that Tommy Flowers, the engineer at the Post Office Research Station at Dollis Hill in north London and who had been responsible for building the Colossus computers, should build the ACE, but because of the secrecy around his wartime achievements and the pressure of post-war work, this was not possible.

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.

The Pilot ACE had 1450 thermionic valves (vacuum tubes), and used mercury delay lines for its main memory. It ran its first program on May 10, 1950, at which time it was the fastest computer in the world with a clock speed of 1 Megaherz.

The first production versions of the Pilot ACE, the English Electric DEUCE, were delivered in the spring of 1955 and thirty one were sold.



















The picture above shows an early De Havilland Comet owned by BOAC (British Overseas Airways Corporation).

Note the windows with right angled corners.




The picture below shows a portion of Comet fuselage demonstrating metal fatigue cracks extending from the corners of one of the windows.



In 1948 Turing joined Max Newman's Computing Laboratory at Manchester University where he assisted development of the Manchester computers and became interested in mathematical biology.

There, he wrote a paper on the chemical basis of morphogenesis, and predicted various oscillating chemical reactions.

In 1952 Turing was prosecuted for homosexual acts when such behaviour was still criminalised in the UK. He accepted treatment with oestrogen injections (chemical castration) as an alternative to prison.

Turing died on 7 June 1954 aged 41 in Wilmslow, Cheshire from cyanide poisoning. An inquest determined his death a suicide - his mother and some others believed it to have been accidental.

In 2009, following an Internet campaign, British Prime Minister Gordon Brown made an official public apology on behalf of the British government for "the appalling way he was treated".

Queen Elizabeth II granted him a posthumous pardon in 2013.



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