The electro-mechanical device Alan Turing designed for breaking Enigma was called the Bombe. It tested possible settings of German Enigma machines and helped British codebreakers identify settings that could produce a known piece of plaintext.
Turing developed the initial British design at Bletchley Park in 1939. The machine built on earlier Polish work, particularly Marian Rejewski's bomba kryptologiczna. Gordon Welchman later added the diagonal board, a major improvement that made the Bombe much more effective. Harold “Doc” Keen and the British Tabulating Machine Company turned the design into working machines.
The Bombe did not simply read Enigma messages automatically. Cryptanalysts first created a likely plaintext fragment, called a crib, and wired a menu into the machine. The Bombe then rejected rotor settings that produced contradictions and left a smaller number of candidates for human examination. The first British machine, named Victory, was installed in March 1940.