Alan Turing’s Legacy: Codebreaking, Computing and Turing’s Law

From his pioneering work at Bletchley Park during the Second World War to his arrest for homosexuality and eventual pardon, we look at the legacy of Alan Turing.

The legacy of Alan Turing’s life and work did not fully come to light until long after his death in 1954. Although his impact on computer science was widely acknowledged, it wasn’t until the 1990s that his role in cracking the Enigma code in the Second World War came to light.

Born in London in 1912, Turing was a brilliant mathematician who studied at both Cambridge and Princeton universities. Before the Second World War he was already working for the British Government’s Code and Cypher School, but in 1939 he took up a full-time role at Bletchley Park - where secret work was carried out to decipher the military codes used by Germany and its allies.

It is estimated that the intelligence produced at Bletchley Park shortened the war by two to four years, and Turing played a central role in this.

Enigma

His main focus was cracking the Enigma code used by the German armed forces to send messages securely.


A four-rotor German Enigma cipher machine 

Polish mathematicians had worked out how to read Enigma messages and shared this information with the British. However, the Germans increased its security at the outbreak of war by changing the cipher system daily, making the task of understanding the code even more difficult.

Turing set about cracking the Enigma messages, inventing a machine known as the Bombe that helped significantly reduce the work of code-breakers. By the mid-1940s German Air Force signals were being read at Bletchley and the intelligence gained from them was helping the war effort.

Hut 8

The breakthrough with Enigma also played a key role in decrypting more complex German naval communications. German U-boats inflicted heavy losses on Allied shipping at the start of the war and the need to understand their signals was crucial. With the help of Enigma material, the naval messages were able to be read from 1941.

Turing headed a team in ‘Hut 8’ at Bletchley Park which carried out cryptanalysis of all German naval signals. This allowed Allied convoys to be diverted away from U-boat packs which was pivotal during the Battle of the Atlantic.

Computing

After the war Turing worked on the design of the ACE (Automatic Computing Engine) at the National Physical Laboratory, which many people see as the forerunner to the modern computer. In 1949 he became Deputy Director of the Computing Machine Laboratory at the Victoria University of Manchester, working on software for one of the earliest stored-program computers - the Manchester Mark 1.


Alan Turing in 1951 © National Portrait Gallery, London

Three years later Turing was arrested for homosexuality – which was then illegal in Britain – and was found guilty of ‘gross indecency’. He avoided a prison sentence by accepting chemical castration but the conviction led to the removal of his security clearance and barred him from continuing with his cryptographic consultancy for the Government Communications Headquarters.

On 8 June 1954 he was found dead from cyanide poisoning at his home, with an inquest ruling that it was suicide.

Pardon and Turing’s Law

In 2013 Turing was given a posthumous royal pardon after bills were submitted in Parliament and the House of Lords.

Chris Grayling, Justice Secretary at the time said: “Turing deserves to be remembered and recognised for his fantastic contribution to the war effort and his legacy to science. A pardon from the Queen is a fitting tribute to an exceptional man.”

In 2016 the Government announced gay and bisexual men convicted of now-abolished sexual offences in England and Wales were to receive posthumous pardons under an amendment dubbed the "Turing law".

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