Joan MURRAY, née CLARKE (1917–1996)

Cryptanalyst and numismatist

7 Larkfields, Headington Quarry, Oxford

Joan Murray (Clarke)

Joan Clarke was born at West Norwood, London, daughter of William Kemp Lowther Clarke, an Anglican clergyman, and his wife Dorothy, née Fulford. She was educated at Dulwich High School and went up to Newnham College, Cambridge, where she gained a double first in Mathematics and was a wrangler.

In 1940 while still an undergraduate she was recruited by Gordon Welchman for the Government Code and Cypher School at Bletchley Park. She was assigned to Hut 8 where she worked closely with Alan Turing, Peter Twinn, and Tony Kendrick to crack the complex German naval Enigma codes which some thought unbreakable. Their task was to intercept messages and anticipate U-boat attacks which were devastating Britain’s Atlantic supply lines. The capture of key cipher documents from German shipping at various times enabled the team to use Turing’s electronic ‘bombe’ machine which could check endless combinations at great speed. Joan was especially adept at using ‘Banburismus’, a procedure based on probability, devised by Turing to reduce dramatically the number of rotor combination readings and thus speed up the process. (The name came from the use of long sheets of paper made in Banbury.) She was unique as the only woman to work in Hut 8 where she fully held her own in the team, working on this and other cyphers and helping the allies to win the battle of the Atlantic. The ingenuity of Joan and her team is credited with shortening the war by at least two years. She was appointed MBE in 1947.

She developed a close friendship with Alan Turing and in 1941 became secretly engaged to him but the engagement was broken off by mutual consent because of Turing’s homosexual tendencies. She remained a very good and supportive friend of Turing for the rest of his life. After the war she worked at GCHQ until her marriage in 1952 to Lt Col Jock Murray, a retired army officer and colleague, when they moved to Crail in Scotland. In 1962 they moved back to Cheltenham and she resumed her work at GCHQ until 1977. She assisted with the writing of the relevant official volume of British Intelligence in the Second World War. She also became a notable numismatist, winning the prestigious Sanford Saltus medal for work on Scottish coinage.

7 Larkfields

In 1991, five years after the death of her husband, she moved to 7 Larkfields, Headington Quarry, Oxford, where she died in 1996. Her profile was raised in The Imitation Game (2014) a film about Alan Turing. Her part was played by the film star Keira Knightley. 


  • Oxford Dictionary of National Biography, article by Ralph Erskine
  • The Secret Life of Bletchley Park (2010) by Sinclair McKay.

The plaque was unveiled on 27 July 2019 at 7 Larkfields by Kerry Howard, independent Bletchley Park researcher and writer. Among those attending were John Clarke, nephew, and other family members, Cllr Altaf Khan (Deputy Lord Mayor of Oxford), representatives from Bletchley Park, and local residents.

Photographs taken at the ceremony:

  • Members of Joan Murray's family
    Walter Roberts, John Clarke, Caroline Roberts, and Charlotte Roberts
  • Invited dignitaries with the speaker
    Cllr Chewe Munkonge (city councillor for Quarry & Risinghurst), Cllr Tim Hallchurch (Cherwell District Council), Cllr Altaf Khan (Deputy Lord Mayor of Oxford), Cllr Roz Smith (city councillor for Quarry & Risinghurst and county councillor for Headington & Quarry), Cllr Les Sibley (Chairman of Oxfordshire County Council), Kerry Howard (speaker), and Cllr Dave Bretherton (Chair of South Oxfordshire District Council)

Oxford Mail, 30 July 2019: “Blue plaque in Oxford for Bletchley Park's Joan Murray (Clarke)


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