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A ‘brilliant’ mathematician who helped break the Nazi Enigma codes at Bletchley Park during World War II has been honoured with a blue plaque outside her childhood home.
The memorial to the late Joan Clarke was unveiled in south London shortly before the commemorations to mark the 80th anniversary of D-Day earlier this summer.
Clarke’s talent with numbers shone through at an early age, when she won several prizes for mathematics while still at school.
In 1936, she won a scholarship to study the subject at Newham College in Cambridge, where she first met Alan Turing. On the outbreak of war, she was snapped up by the Government Code and Cypher School (GC&CS) at Bletchley Park, where Turing poached her to work alongside him in the now-legendary Hut 8.
Clarke worked closely with Turing and others on deciphering the code used by the German Navy, which was generated by letter-scrambling rotors in the Enigma machine.
Putting her maths skills to use, Clarke worked out probable rotor starting positions, until the later capture of an Enigma machine enabled Hut 8 to speed up decryption. The intelligence provided greatly reduced the number of Allied ships sunk in the war.
Hut 8’s work intensified in the build-up to D-Day to decode German weather signals and provide intelligence support to special operations and bombing raids ahead of the invasion.
In spring 1941, Turing proposed to Clarke – much to her surprise. As she told a BBC documentary in 1992: ‘I really didn’t hesitate in saying yes, and then he knelt by my chair and kissed me, though we didn’t have very much physical contact.’
The engagement later ended on account of Turing’s homosexuality – then illegal in Britain – but their friendship survived. Clarke was portrayed by Keira Knightley in the 2014 Turing biopic The Imitation Game, which starred Benedict Cumberbatch.
Appointed MBE in 1946, Clarke had to wait until 1948 – when women were finally permitted to graduate from Cambridge – to receive her degree. She later worked at RAF Eastcote, decoding communications between Soviet agents, and at GCHQ in Cheltenham. Clarke retired in 1983, and died 13 years later aged 79.
The plaque, at 193 Rosendale Road in West Dulwich, describes her simply as a ‘mathematician and codebreaker.’
Image: English Heritage
