After two years at Princeton, developing ideas about secret ciphers, Turing returned to Britain and joined the government’s code-breaking department. In July 1939, the Polish Cipher Bureau passed on crucial information about the Enigma machine, which was used by the Germans to encipher all its military and naval signals. After September 1939, joined by other mathematicians at Bletchley Park, Turing rapidly developed a new machine (the ‘Bombe’) capable of breaking Enigma messages on an industrial scale