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Faces of HPC: Joan Clarke

Joan Clarke worked closely with Alan Turing in ‘Hut 8’ at Bletchley Park - made famous for the work deciphering the Enigma Ciphers. Clarke’s personal contributions to the work is still largely unknown due to the secrecy of the work, although she was appointed MBE in 1947 for her work during World War Two.


Clarke was the only woman to work on the Enigma project, alongside Alan Turing, during WW2. Recruited straight from her education at the University of Cambridge, where Clarke excelled but was not awarded a full-degree as this privilege wasn’t given until women until 1948, Clarke started out in clerical work before eventually rising to deputy head of the now infamous ‘Hut 8’ where the Enigma code was broken, a key turning point of WW2.


Joan Clarke was born in West Norwood, London, UK. Born into a family with three brothers and one sister, and the daughter of a Reverend, Clarke quickly excelled in her education, being awarded a scholarship in 1936 to attend Newnham College at the University of Cambridge.

Clarke went on to be awarded a double first in Mathematics. However, she was unable to gain a full degree as women were not granted degrees by Cambridge until 1948.

On completing her studies she was recruited into the Government Code and Cypher School (GCCS), which was formed in 1939 with the purpose of breaking German cyphers during the Second World War. Clarke was sent to work at Bletchley Park on 17 June 1940 where she became one of the ‘The Girls’ (never referred to as women) that performed clerical work supporting the code-breaking efforts. At this time cryptography was not viewed as a job suitable for women.

Within days of starting work Clarke was given additional duties and joined the team in ‘Hut 8’ - made famous as the place where Turing and others worked to break the Enigma ciphers. Clarke was the only woman to use ‘Banburismus’: the cryptanalytic process developed by Alan Turing. The Head of Hut 8, Hugh Alexander, later described Clarke as ‘one of the best Banburists in this section’.

During this time, in order to receive any pay beyond ‘Clerical Assistant’ Clarke was promoted to a ‘Linguist’ despite not speaking any other languages. Clarke reportedly delighted completing forms with her job title ‘Linguist’ alongside ‘Languages - none’. However, Clarke was never paid the equivalent of her male colleagues.

The ciphers that Clarke and her colleagues broke were the most complex that Bletchley Park worked on, and yet her job required real-time deciphering of the codes. The results of Clarke’s work resulted in immediate military action on U-boats, saving thousands of lives.

Clarke was the only woman to work directly on the cracking of the German Enigma ciphers, and with the information obtained in the capture of the cipher equipment and codes, Clarke and her team were able to reduce the amount of shipping sunk from 282,000 tons to 62,000 tons per month.

Clarke later became deputy head of Hut 8 in 1944, but could not progress further or receive more pay due to being a woman.

During her time at Bletchley Park, Clarke developed a close friendship with Alan Turing. In 1941 Turing proposed marriage to Clarke and they remained briefly engaged despite an open acknowledgment of Turing’s homosexuality between them. The engagement was short lived, with the engagement being called off just a few months later by Turing who believed the marriage would fail. Clarke and Turing remained close friends until his death in 1954.

Clarke rarely commented on her work on the Enigma project up until her death in 1996. Along with the few other female codebreakers at Bletchley, Clarke’s work as a human ‘computer’ to break codes is still rarely acknowledged, with the focus on male professors who dominated the work.

After the war Clarke went on to work for Government Communications Headquarters (GCHQ).


BBC News, "Joan Clarke, Woman who cracked Enigma cyphers with Alan Turing"; http://www.bbc.co.uk/news/technology-29840653, last accessed 30/9/2017
Wikipedia Foundation, "Joan Clarke", https://en.wikipedia.org/wiki/Joan_Clarke, last accessed 30/9/2017

Last updated: 02 Oct 2017 at 20:17