At Bletchley Park

Abstract

This chapter summarizes Turing’s principal achievements at Bletchley Park and assesses his impact on the course of the Second World War. On the first day of the war, at the beginning of September 1939, Turing took up residence at Bletchley Park, the ugly Victorian mansion in Buckinghamshire that served as the wartime HQ of Britain’s military codebreakers (Fig. 9.1). There Turing was a key player in the battle to decrypt the coded messages generated by Enigma, the German forces’ typewriter-like cipher machine. Germany’s army, air force, and navy transmitted many thousands of coded messages each day during the Second World War. These ranged from top-level signals, such as detailed situation reports prepared by generals at the battlefronts and orders signed by Hitler himself, down to the important minutiae of war such as weather reports and inventories of the contents of supply ships. Thanks to Turing and his fellow codebreakers, much of this information ended up in Allied hands—sometimes within an hour or two of its being transmitted. The faster the messages could be broken, the fresher the intelligence that they contained, and on at least one occasion the English translation of an intercepted Enigma message was being read at the British Admiralty less than 15 minutes after the Germans had transmitted it. Turing pitted machine against machine. Building on pre-war work by the legendary Polish codebreaker Marian Rejewski, Turing invented the Enigma-cracking ‘bombes’ that quickly turned Bletchley Park from a country house accommodating a small group of thirty or so codebreakers into a vast codebreaking factory. There were approximately 200 bombes at Bletchley Park and its surrounding outstations by the end of the war. As early as 1943 Turing’s machines were cracking a staggering total of 84,000 Enigma messages each month—two messages every minute. Chapter 12 describes the bombes and explains how they worked. Turing also undertook, single-handedly at first, a 20-month struggle to crack the especially secure form of Enigma used by the North Atlantic U-boats. With his group he first broke into the current messages transmitted between the submarines and their bases during June 1941, the very month when Winston Churchill’s advisors were warning him that the wholesale sinkings in the North Atlantic would soon tip Britain into defeat by starvation.