Gordon Welchman - at Bletchley Park

At Bletchley Park

Just before World War II, Welchman was invited by Commander Alastair Denniston to join the Government Code & Cypher School at Bletchley Park, in case war broke out. He was one of four early recruits to Bletchley (the others being Alan Turing, Hugh Alexander, and Stuart Milner-Barry), who all made significant contributions at Bletchley, and who became known as 'The Wicked Uncles'. They were also the four signatories to an influential letter, delivered personally to Winston Churchill in October 1941, asking for more resources for the code-breaking work at Bletchley Park. Churchill responded with one of his 'Action This Day' stickers.

Welchman envisaged an enhancement to Alan Turing's improved design of the Polish electromechanical Enigma-cipher-breaking machine, the bombe. Welchman's enhancement, the 'diagonal board', rendered the device substantially more efficient in the attack on ciphers generated by the German Enigma machine. Bombes became the primary mechanical aid in breaking Enigma ciphers during the war, by speeding up the search for current settings being used with the Enigma machines; these were changed often, initially at least once per day.

Welchman was head of Hut Six, the section at Bletchley Park responsible for breaking German Army and Air Force Enigma ciphers. In 1943 he became Assistant Director in charge of mechanisation, and also had responsibility for cryptographic liaison with the USA.