Alan Turing

Mathematician, cryptanalyst and former resident of Guildford

The Turing statue by John M Mills,
at University of Surrey Campus,
unveiled in 2004. (Photograph: Di Stiff)

Alan Turing (1912-1954), OBE, FRS, has been described as the father of the modern computer. His life's work had an immense impact on the history of the 20th century, both in breaking the German 'Enigma' code in World War II, and in laying the foundations of computer science. However, Turing was judicially persecuted for his homosexuality, which probably led to his suicide two years later.

Early life
Turing was the second son of an Indian colonial family, who later settled in Ennismore Avenue, Guildford. He graduated from Kings College Cambridge in 1934 and was elected a fellow. In 1936 he published 'On computable numbers' which introduced the idea of a machine (the 'Turing machine') which might be capable of making any mathematically imaginable computation. Turing perceived that such a machine could be 'universal', that is, it could theoretically replace any other machine.

Enigma
Probably Turing's most famous achievement was his contribution to the breaking of the Enigma, the code used by the Germans to encrypt secret messages during the Second World War. In March 1940 Turing's device, later known as the Turing Welchman Bombe, came into operation at Bletchley Park. The Bombe, a series of electromechanically driven rotors, used fragments of decoded Enigma text ('crib') to calculate any matching setting of the corresponding rotors in the Enigma encoder, which were used to scramble the messages. The Bombe was an ingenious logic engine, designed to short circuit on any calculation contradicting the 'crib', thus freeing computational power to check further settings. In 1945, Turing was awarded an OBE for his war work, which also included a secure voice communications machine ('Delilah').

Turing's post-war work, mostly while based at Manchester University, included research on the earliest stored-program computers, definitions of 'artificial intelligence' (the 'Turing test') and mathematical biology.

English Heritage Blue plaque in Ennismore Avenue,
Guildford, the home of Turing’s parents. (Photograph: Di Stiff)

Homosexuality and ‘treatment’
Although shy, Turing had not concealed his homosexuality from his friends. Tragically, Turing's short affair with 19 year old Arnold Murray in 1952 brought his private life into conflict with the society of his day. Discovering that Murray was an accomplice to a burglary of his house, Turing reported him to the police, making a full statement on their relationship. Both Turing and Murray were prosecuted for homosexual acts, then illegal whether in private or in public, under section 11 of the Criminal Law Amendment Act 1885. Turing had been unashamed in his admission, although he wrongly believed that the law was about to change (it would not until 1967). Although the law was an old one, a chemical hormonal 'treatment' programme as an alternative to punishment by imprisonment was new in the early 1950s. Turing submitted to the treatment (and its unpleasant side effects), probably in order to be able to pursue his work, although his criminalisation brought worries about his employment and barred his entry to the USA.

Suicide and apology
Turing left no suicide note before eating an apple apparently laced with cyanide. His motivation is unknown, but the humiliation he had received by the prosecution seems likely to have influenced his state of mind. Turing's ashes were buried at Woking Crematorium beside those of his father. He has been memorialised elsewhere, including at Sackville Memorial Park, Manchester, and the University of Surrey, Guildford.

In September 2009 the British Government issued a formal apology for Turing's treatment, saying 'he deserved better'.