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 4 — The Second World War

In 1938 Turing was offered a temporary post at Princeton by von Neumann but instead returned to Cambridge. He had no University lectureship; in the year 1938-9 he lived on his King's College fellowship, as logician and number theorist. Unusually for a mathematician, he joined in Wittgenstein's classes on the philosophy of mathematics; unusually again, he engineered gear-wheel parts for a special machine to calculate the Riemann Zeta-function.

The Enigma cipher machine
Publicly, he sponsored the entry into Britain of a young German Jewish refugee. Secretly, he worked part-time for the British cryptanalytic department, the so-called Government Code and Cypher School. His appointment marked the first scientific input into a hitherto arts-based department. That revolution was caused by the failure of pre-scientific methods to penetrate the mechanical Enigma cipher used by Germany. No significant progress was made, however, until the gift of vital ideas and information in July 1939 from Poland, where mathematicians had been employed on the problem much earlier.
Upon British declaration of war on 3 September, Turing took up full-time work at the wartime cryptanalytic headquarters, Bletchley Park. The Polish work was limited as it depended upon the very particular way the Germans had been using the Enigma. One of their ideas was embodied in a machine called a Bomba. The way forward lay in Turing's generalisation of the Polish Bombe into a far more powerful device, capable of breaking any Enigma message where a small portion of plaintext could be guessed correctly. Another Cambridge mathematican, W. G. Welchman, made an important contribution, but the critical factor was Turing's brilliant mechanisation of subtle logical deductions.

From late 1940 onwards, the Turing-Welchman Bombe made reading of Luftwaffe signals routine. In contrast, the more complex Enigma methods used in German Naval communications were generally regarded as unbreakable. Happy to work alone on a problem that defeated others, Turing cracked the system at the end of 1939, but it required the capture of further material by the Navy, and the development of sophisticated statistical processes, before regular decryption could begin in mid-1941. Turing's section 'Hut 8', which deciphered Naval and in particular U-boat messages, then became a key unit at Bletchley Park. By the end of 1941, as the United States entered the war, the battle of the Atlantic was moving towards Allied advantage. On 1 February 1942, the Atlantic U-boat Enigma machine was given an extra complication and this advantage was suddenly wiped out: nothing could be decoded and catastrophe loomed.

Besides illustrating the always razor-edge state of the war of wits, this crisis brought about a new ingredient in Alan Turing's experience: electronic technology made its first appearance at Bletchley Park as telephone engineers were pressed into an effort to gain ever higher speeds of mechanical working. As it turned out, however, the electronic engineers found themselves called upon to mechanize the breaking of the 'Fish' material: messages enciphered on the quite different system used for Hitler's strategic communications. Here again Turing's statistical ideas underlay the methods employed, though it was M. H. A. Newman who played the organising role. The conjunction of Turing's thoughts with the practicality of large-scale electronic machinery, arising from this technical U-boat Enigma change, came to have momentous consequences.

Continue the short biography

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

© Andrew Hodges 1995












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