CHAPTER 9
At Bletchley Park
jack copeland
This chapter summarizes Turing’s principal achievements at Bletchley Park and assesses his
impact on the course of the Second World War.
war party
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.^1
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 situa-
tion 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.^2
Bomber
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 code-
breakers into a vast codebreaking factory.^3
There were approximately 200 bombes at Bletchley Park and its surrounding outstations
by the end of the war.^4 As early as 1943 Turing’s machines were cracking a staggering total of