Bletchley Park

Bletchley Park, Victorian mansion situated 80 km. (50 mi.) north-west of London. Known as Station X, from 1939 it was the site of the British Government Code and Cypher School (Government Communications HQ from 1942). This had been formed in 1919, from the cryptanalytical sections of the Admiralty (Room 40 O.B.) and the War Office, ‘to advise as to the security of codes and cyphers used by all Government departments and to assist in their provision’, but it was also secretly ordered to ‘study the methods of cypher communications used by foreign powers’. This meant that its staff worked to break those ciphers and it was, in fact, not a school at all but a highly secret organization which came under the aegis of the head of MI6.

In 1939 the staff, headed by Alistair Denniston, numbered about 150, but it grew so rapidly that wooden huts were erected to accommodate the overflow. By late 1942 the numbers had risen to about 3,500, and to more than 10,000 by 1945. Some were civilians (see Turing); others came from the armed services of several nations, including France, Poland, and the USA. They worked on the decryption of German and Japanese hand codes and ciphers; on the ENIGMA and PURPLE machine ciphers, which produced ULTRA and MAGIC intelligence; and on the Geheimschreiber transmissions. Initially, ‘bombes’—devices which simulated the workings of an ENIGMA—helped decrypt signals, but by June 1944 the first electronic digital computer, COLOSSUS II, was being used. Staff in Hut 6 deciphered the German Army and Luftwaffe ENIGMA signals, the latter task often being simplified by the signals sent by FLIVOS; those in Hut 3 translated and interpreted them, and dispatched the resulting intelligence to Special Liaison Units and other recipients; and those in Huts 4 and 8 dealt with naval ENIGMA signals which were passed to the Naval Intelligence Division.

Bletchley had three cryptanalytical outposts overseas: the Combined Bureau, Middle East, the Wireless Experimental Centre at Delhi, and the Far East Combined Bureau, all of which had their own outposts.

The Germans never knew the purpose of Bletchley Park, though at least one person mentioned in the Black Book was listed as having gone ‘to Bletchley’.

Bibliography

Hinsley, F. H. , British Intelligence in the Second World War, 5 vols. (London, 1979–90).
—— and Stripp, A. (eds), Codebreakers: The Inside Story of Bletchley Park (Oxford, 1993)
Lewin, R. , Ultra Goes To War (London, 1978).
Smith, M. , The Emperor's Codes: Bletchley Park and the Breaking of Japan's Secret Ciphers (London, 2000).
Stripp, A. , Codebreaker in the Far East (London, 1989).