Rebuilding the Bombe [Enigma code breaking machine]

Film makers who wanted to recreate the machines that played a vital part in breaking the German Enigma code were able to turn for advice to a group of engineers who are building their own working replica. Both film and book take their name from the coding device used by the German military to communicate battle plans. The machine was almost unbreakable in its sophistication, but procedural flaws such as reusing code book settings, made it vulnerable, and as early as 1932 Polish experts had broken the Enigma cipher and constructed a machine, the Bomba, that led to the cyphers being broken for the first time. Just before the war, they handed their work over to the British and French, and it was at Bletchley Park that mathematician Alan Turing and his colleague Gordon Welchman laid the foundations for the Bombe, electro-mechanical machine that speeded up the codebreaking process. When it came to creating several replica Bombes they commissioned South London based Asylum Models and Effects to make six machines. Asylum in turn went to a group of people who have learned the hard way the complexity of these early computing devices-a team which with support from the Bletchley Park Trust and Computer Conservation Society is rebuilding its own working Bombe. The 'Target Machine' that is under construction is based on a parts list from October 1943 for one of 68 devices built to a similar specification to decode messages from three-wheel Enigmas. This article describes the project and the history behind the building of the first Bombe machines.