Alan Turing: a short biography by Andrew Hodges

This short on-line biography of Alan Turing is based on the entry I wrote for the British Dictionary of National Biography in 1995. The eight parts correspond roughly to the eight sections of my full biography Alan Turing: the enigma.

There are no hyperlinks in the text. For links and for more images, go to the corresponding page of the Alan Turing Internet Scrapbook.

Part 5 — Emergence of the Computer

By 1942 Alan Turing was the genius loci at Bletchley Park, famous as 'Prof', shabby, nail-bitten, tie-less, sometimes halting in speech and awkward of manner, the source of many hilarious anecdotes about bicycles, gas masks, and the Home Guard; the foe of charlatans and status-seekers, relentless in long shift work with his colleagues, mostly of student age. To one of these, Joan Clarke, he proposed marriage, and was gladly accepted. But then he retracted, telling her of his homosexuality.

Turing crossed the Atlantic in November 1942, for highest-level liaison not only on the desperate U-boat Enigma crisis, but on the electronic encipherment of speech signals between Roosevelt and Churchill. Before his return in March 1943, logical weaknesses in the changed U-boat system had been brilliantly detected, and U-boat Enigma decryption was effectively restored for the rest of the war. With the battle of the Atlantic regained for the Allies, crisis resolved, chess champion C. H. O'D. Alexander, hitherto Turing's deputy, took charge of Hut 8.

Turing became an all-purpose consultant to the by now vast Bletchley Park operation. As such he saw the 'Fish' material cracked by the Colossus machines, brought into operation just before D-Day, demonstrating the feasibility of large-scale digital electronic technology. Turing himself devoted much time to learning electronics: ostensibly for creating his own, elegant speech secrecy system, which he effected with the aid of one assistant, Donald Bayley, at nearby Hanslope Park. But he had another and more ambitious end in view: in the last stage of the war (for his part in which he was awarded an OBE) he planned the embodiment of the Universal Turing Machine in electronic form, or in effect, invented the digital computer.

In 1944, at the invasion of Normandy that Allied control of the Atlantic allowed, Alan Turing was almost uniquely in possession of three key ideas:

  • his own 1936 concept of the universal machine
  • the potential speed and reliability of electronic technology
  • the inefficiency in designing different machines for different logical processes.
Combined, these ideas provided the principle, the practical means, and the motivation for the modern computer, a single machine capable of handling any programmed task. He himself was as eager as anyone in the world to bring them together, and was spurred even more by a fourth idea: that the universal machine should be able to acquire and exhibit the faculties of the human mind. Even in 1944 he spoke to Donald Bayley of 'building a brain'.

Turing was captivated by the potential of the computer he had conceived. Although his 1936 work had shown the absolute limitations of the computable, he had become fascinated by what Turing machines could do, rather than by what they could not. He had long abandoned his youthful expectations of finding free will or free spirits through quantum mechanics. His later thought was strongly determinist and atheistic in character. And by the end of the Second World War he had turned against the tentative idea that there were steps of 'intuition' in human thought corresponding to uncomputable operations. Instead, he held that the computer would offer unlimited scope for practical progress towards embodying intelligence in an artificial form.

For the second time, he experienced being pre-empted by a parallel American publication, in this case the EDVAC plan for an electronic computer, with Von Neumann's name attached. Nonetheless, this publication when it appeared in June 1945 worked in practice to Turing's advantage, American competition stimulating the National Physical Laboratory to plan a rival project, to which he was appointed a Senior Principal Scientific Officer. Turing despised his nominal superior J. Womersley, but at least initially this applied mathematician showed a rapid appreciation of the scope of Turing's ideas, and with a eye for acronyms steered Turing's design towards formal approval in early 1946 as the Automatic Computing Engine, or ACE.

Continue the short biography

For links and more pictures go to the corresponding
Alan Turing Internet Scrapbook page.

© Andrew Hodges 1995












Alan Turing
Home Page


Alan Turing: the enigma


The background for this Page was generated by Roy Williams and Bruce Sears from a non-linear equation of the kind Alan Turing first studied.