Alan Turing (London, 1912 – Wilmslow, 1954), a mathematician at the Government Code and Cypher School at Bletchley Park, designs in 1939 the Bombe — an electromechanical machine that automates the search for Enigma settings — building on the Polish Bomba developed by Rejewski, Różycki, and Zygalski in 1938. Turing's critical improvement is the use of logical chains of implication (cribs) to drastically reduce the search space; Gordon Welchman added the diagonal board, multiplying its efficiency. At its peak, Bletchley Park operated more than 200 Bombes, decrypting thousands of messages daily. Turing and his team's work remained classified until 1974 (partial revelation by F.W. Winterbotham) and fully until the 2000s. Turing was prosecuted in 1952 for homosexuality, chemically castrated, and died in 1954. He received a posthumous royal pardon in 2013. His contribution to the Allied victory was not publicly recognized in his lifetime.