Recruiting volunteers, at one time numbering 60, the task of reconstructing the one-ton Bombe with its countless components and moving parts began.Īlthough a few parts were sourced from the period, most were re-manufactured from the original drawings. As a former employee of ICL, John was able to make contact with some of the original engineers. As a tribute to the Bletchley Park codebreakers, John Harper, a retired engineer, decided it was timely to reconstruct a Bombe in the park which had just been saved from redevelopment.īTM, the original Bombe manufacturers, through a series of mergers, became ICL in the late 1960s. Reconstructing the Bombeįorty years after the war, GCHQ released some 2000 BTM documents and drawings about the Bombe. Many of the machines were located at out-stations, including Stanmore and Eastcote.Īfter the war, about 50 Bombes were temporarily retained, and some, according to official documents, continued to run. Huge amounts of intercepted traffic were deciphered, supplying invaluable information about enemy operations. Throughout the war the operation built around 211 Bombe machines and broke many keys on a daily basis. The engineering and construction of the original Bombes was the work of the British Tabulating Machine Company – BTM (which was later responsible for the 1950s HEC computer now at TNMOC). The first Turing-Welchman Bombe based machine, known as Agnus Dei or simply Agnes, became operational in August 1940. Turing realised that his approach was capable of being mechanised, and his invention of the Bombe, together with Gordon Welchman's diagonal board, (which dramatically reduced the number of invalid stops - false positives) increased throughput to the point that the Bombe became a major success. This approach was aided by the fact that no letter on the Enigma could be represented by itself in an enciphered message. Turing's attack was based on the use of ‘cribs’ (comparing patterns of the encrypted message and a known portion of plain text) to break the key. Because of changes to the German operating procedures and the introduction of extra wheels, the Polish Bomba was now obsolete. At Bletchley Park, attempts to decipher messages began.Īt the Park, Alan Turing was asked to find a way to break Enigma messages. With the outbreak of war in 1939, ‘Y’ Intercept stations around Britain, and indeed in many parts of the world, intercepted all sorts of communications, including Enigma messages. Using a Bomba machine in 1938, they supplied valuable pre-war information from the simpler Enigma cipher techniques then being used. Prior to the war, in the 1920s, three Polish mathematicians were the first to break the Enigma cipher. Some keys would be broken within 2-4 hours, some would never be broken – speed was always of the essence. It was the task of the Bombe to discover the daily key - wheel order, wheel settings and plugboard configuration - to enable the 3-5,000 Enigma messages intercepted each day to be deciphered.
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