Turing, on the basis of his published work, was recruited to serve in the Government Code and Cypher School, located in a Victorian mansion called Bletchley Park in Buckinghamshire. The task of all those so assembled — mathematicians, chess champions, Egyptologists, whoever might have something to contribute about the possible permutations of formal systems — was to break the Enigma codes used by the Nazis in communications between headquarters and troops. Because of secrecy restrictions, Turing's role in this enterprise was not acknowledged until long after his death. And like the invention of the computer, the work done by the Bletchley Park crew was very much a team effort. But it is now known that Turing played a crucial role in designing a primitive, computer-like machine that could decipher at high speed Nazi codes to U-boats in the North Atlantic.

After the war, Turing returned to Cambridge, hoping to pick up the quiet academic life he had intended. But the newly created mathematics division of the British National Physical Laboratory offered him the opportunity to create an actual Turing machine, the ACE or Automatic Computing Engine, and Turing accepted. What he discovered, unfortunately, was that the emergency spirit that had short-circuited so many problems at Bletchley Park during the war had dissipated. Bureaucracy, red tape and interminable delays once again were the order of the day. Finding most of his suggestions dismissed, ignored or overruled, Turing eventually left the NPL for another stay at Cambridge and then accepted an offer from the University of Manchester where another computer was being constructed along the lines he had suggested back in 1937.

Since his original paper, Turing had considerably broadened his thoughts on thinking machines. He now proposed the idea that a machine could learn from and thus modify its own instructions. In a famous 1950 article in the British philosophical journal Mind, Turing proposed what he called an "imitation test," later called the "Turing test." Imagine an interrogator in a closed room hooked up in some manner with two subjects, one human and the other a computer. If the questioner cannot determine by the responses to queries posed to them which is the human and which the computer, then the computer can be said to be "thinking" as well as the human.

Turing remains a hero to proponents of artificial intelligence in part because of his blithe assumption of a rosy future: "One day ladies will take their computers for walks in the park and tell each other, 'My little computer said such a funny thing this morning!'"

Unfortunately, reality caught up with Turing well before his vision would, if ever, be realized. In Manchester, he told police investigating a robbery at his house that he was having "an affair" with a man who was probably known to the burglar. Always frank about his sexual orientation, Turing this time got himself into real trouble. Homosexual relations were still a felony in Britain, and Turing was tried and convicted of "gross indecency" in 1952. He was spared prison but subjected to injections of female hormones intended to dampen his lust. "I'm growing breasts!" Turing told a friend. On June 7, 1954, he committed suicide by eating an apple laced with cyanide. He was 41.

TIME senior writer Paul Gray writes on a Turing machine

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