Codebreaking at Bletchley Park

At a country house north-west of London, thousands of codebreakers, most of them women, broke German Enigma and Lorenz ciphers. Alan Turing's bombe machines and Colossus, an early programmable electronic computer, sped up the work. Intelligence code-named Ultra helped win the Battle of the Atlantic and plan D-Day, and the work stayed secret until the 1970s.