Joan Clarke - The Best Banburist at Bletchley Park

"The Imitation Game" starred Benedict Cumberbatch as Enigma Genuis, Alan Turing and Keira Knightly as Joan Clarke. Clarke was the English cryptanalyst and numismatist who worked alongside Turing as a top code-breaker at Bletchley Park and who was also engaged to him briefly.

This film, and Joan's story have some connections for me. I had once worked near Bletchley Park and knew it very well. My partner was lucky enough to actually work on the set  of The Imitation Game for a few weeks, ensuring no modern day cars or traffic could be heard, whilst the location filming took place. (He was even more delighted to be given an extra a Hot Dog at the catering truck by Actor Charles Dance who was also in the cast),

Before I went to see the movie myself, I wanted to know who Joan Clarke was. What was her background and why was her particular role in breaking the Enigma Code during World War II  so important and significant?

 KEIRA KNIGHTLY AS JOAN CLARKE

POSTER FOR THE FILM (2O14)

TRAILER FOR THE IMITATION GAME

Joan Elisabeth Lowther Clarke was born on 24 June 1917 in West Norwood, London, the youngest child of Dorothy (née Fulford) and the Rev William Kemp Lowther Clarke, a clergyman. She had three brothers and one sister.

She attended Dulwich High School for Girls in south London and won a scholarship to attend Newnham College, Cambridge where she gained double first degree in mathematics and was a Wrangler. By 1939 she had completed Part I and II of her Mathematics Tripos, and completed Part III (Honours) in 1940. However this was merely the title of her degree, as Cambridge did not admit women to "full membership of the body academic" until after the end of the Second World War. In 1939 Clarke was awarded the distinguished Philippa Fawcett Prize and in 1939-1940 the Helen Gladstone Scholarship.

Her Geometry supervisor, and fellow  Bletchley Park codebreaker, Gordon Welchman recruited her to the Government Code & Cipher School in June 1940. After a period of clerical work, Joan’s abilities soon led her to becoming one of the few women codebreakers at Bletchley Park.

Joan worked in the section known as Hut 8, and quickly became one of the practitioners of Banburismus, a cryptanalytic process developed by Alan Turing which reduced the need for bombes. Hugh Alexander, head of Hut 8 from 1943 to 1944, described her as "one of the best Banburists in the section".

Records describe Clarke as ‘congenial but shy, gentle and kind, non-aggressive and always subordinate to the men in her life‘ - qualities that would allow her to conform within the male dominated world of Bletchley Park. She was well-respected by her male peers and became Deputy Head of Hut 8 in early 1944, Code breaking was almost entirely done by men during the war. There were only one or two occasions were women held leadership roles at Bletchley Park.

Clarke was paid £2 per Week - less than the men - and felt that she was prevented from progressing further by her sex. A pay rise was engineered to recognise Joan’s abilities and contributions to the team. She was promoted to Linguist even though she spoke no other language. Joan ‘enjoyed answering a questionnaire with ‘Grade: Linguist, Languages: none’. The Deputy Director at Bletchley Park, Commander Edward Travis, later told her that she might have to enroll in the WRNS (Women's Royal Naval Service) in order to earn significantly more money, but Clarke did not wish to pursue this route.

Alastair Denniston, who was to become the first Head of Bletchley Park, at one time actually shared the German belief that the military Enigma was invincible; he is recorded as telling his fellow code breakers  "all German codes were unbreakable". Joan Clarke and her colleagues were destined to prove him wrong. Initially, Clarke was not exactly told what the job would entail, only that  the work didn't really need mathematics but mathematicians tended to be good at it.

William F Friedman, the founder of modern US cryptology wrote that a code breaker required unusual powers of inductive and deductive reasoning, much concentration, perseverance and a vivid imagination. The fact that Joan Clarke was able to move so quickly into the male cryptology area at Bletchley Park indicates she possessed these attributes.

The Naval Enigma was different to the Army and Luftwaffe Enigma and more complex to break. Firstly, two extra wheels had been added so there was now a choice of three from five giving a total number of 336 possible wheel orders. Secondly, to give added security, a different indicator system was applied; instead of transmitting the indicators directly, they were super enciphered using bigram tables.

The need for breaking the Naval Enigma code was growing greater by the day. By mid 1940, following the German occupation of France, German U-Boats now had easy access to the Atlantic from the Bay of Biscay. Britain had become extremely dependent on imports and was importing half of its food and all of its oil. The provisions now had to come across the Atlantic from North America and the convoys rapidly become targets for the U-boats. At one stage, Britain was only three days from running out of food and therefore it was crucial the Naval Enigma code was broken.

In early May 1940, matched plaintext and Enigma cyphertext became available from a German patrol boat, Schiff 26, captured off the Norwegian Coast. Joan Clarke's first task on arriving at Bletchley Park was to use a new key-finding aid called the Bombe, against the recovered data. This successfully resulted in Clarke and her colleagues breaking approximately six days of April traffic over a period of three months.

By the end of 1940 rotors VI, VII and VIII had been recovered and a library of cribs built up - the cribs were assembled by using anticipated text from German weather ships that were relaying messages in the German Meteorological cipher (which was easier to decipher than the dolphin cipher). This provided Clarke and the team, with the knowledge of what information to expect in a message and how the Naval indicator system worked.

Turing had invented a new codebreaking technique called Banburismus. Turing's method exploited the German cryptographic mistake of having different positions of turnover for each wheel. Professor Jack Good, who also worked on Banburismus, has since said that it was the first example of Sequential Analysis and describes it as  "a complicated but enjoyable game".

There were eight male Banburists and Joan Clarke was the only female. However, she was so enthusiastic and fascinated with the technique that she would sometimes be unwilling to hand over her workings at the end of her shift and would continue to see if a few more tests would produce a result. Clarke devised a method of her own to speed up the technique, and she was told, to her surprise, that she had used pure Dillysimus. This was a method which had been invented by Dillwin (Dilly) Knox, one of the few cryptographic experts of World War One, who had originally headed the attack on the German enigma.

Banburismus was impossible without the Bigram substitution tables and therefore without them, very little progress against the Naval Enigma was accomplished. The breakthrough came in February and June 1941, when trawlers were captured along with cipher equipment and codes. Clarke and her co-workers successfully performed Banburismus for two years, only stopping in August 1943 when ultra fast Bombes became available.

The successful results of their efforts were evident immediately. Between March and June 1941, the Wolf Packs (a term used to describe the mass attack tactics used against convoys by U-boats), had sunk 282,000 tons of shipping a month. From July, the figure dropped to 120,000 tons a month and by November, to 62,000 tons.

Clarke and fellow code-breaker Alan Turing became very good friends at Bletchley Park. Clarke and Turing had actually met previously to working at Bletchley Park, as Turing was a friend of her older brother. Turing would arrange their shifts so they could be working together, as well as spending a lot of their free time together.

In the spring of 1941, Turing proposed marriage to Clarke and subsequently introduced her to his family. After admitting his homosexuality to his fiancée, who was reportedly "unfazed" by the revelation, their engagement continued.  Choosing to keep their relationship secret from their colleagues, they talked of the future and Turing told her of his desire to have children.

They shared many interests, both were keen chess players and, as Clarke had studied Botany at school, she shared Turing's lifelong enthusiasm of the growth and form of plant life. When Turing wrote his account of the Enigma Theory for the use of new recruits in Hut 6 and Hut 8, (known at Bletchley Park as "Prof's book") he used Joan Clarke as his 'guinea pig' - she had to read and trial it, checking that it was understandable for them.

In the late summer of 1941, following a holiday in North Wales, their engagement ended by mutual consent, because of Turing's belief that the marriage would  ultimatley be a failure because of his homosexuality.

My Engagement to Alan Turing by Joan Clarke (later Murray) is an extract from the 1992 Horizon programme about Alan Turing featuring Joan. In this short extract from the original programme you can hear Joan talk about Alan’s proposal of marriage:

The team continued to break the Naval Enigma until the end of the war. The war in the west officially ended at midnight on 9 May 1945. By March 1946, all the workers had vacated Bletchley Park and every scrap of evidence of their secret code breaking exploits was disposed of.

Clarke was to remain friends with Turing for the rest of his life. Years later, after they had both left Bletchley Park, Turing revealed in a letter to Clarke that he "did occasionally practice" his homosexuality and that he had been "found out". Homosexuality was illegal at this time, with imprisonment or chemical castration the punishment for offenders.

In 1952 in Manchester, Alan Turing was convicted of "acts of gross indecency" following admission to a relationship with another man. In his defense, Turing said he did not consider he had done anything wrong. As a result of the conviction, Turing was given oestrogen injections for a year, and shortly afterwards committed suicide.

Cast of The Imitation Game talk about why Alan Turing is important to British history

After the war Clarke worked for GCHQ where she met Lieutenant-Colonel John Kenneth Ronald Murray, a retired army officer who had served in India. They married on 26 July 1952 in Chichester Cathedral; the union was childless. Shortly after their marriage John Murray retired from GCHQ due to ill health and the couple moved to Crail in Scotland. They returned to work at GCHQ in 1962 where Clarke remained until 1977 when she retired aged 60.

Clarke was a gifted numismatist. She established the sequence of the complex series of gold unicorn and heavy groat coins that were in circulation during the reigns of James III and James IV of Scotland. In 1986, her research was recognised by the British Numismatic Society when she was awarded the Sanford Saltus Gold Medal. Issue #405 of the Numismatic Circular described her paper on the topic as "magisterial".

Following her husband's death in 1986, Clarke moved to Headington, Oxfordshire, where she continued her research into coinage.

.After her retirement, Clarke also assisted Sir Harry Hinsley on what became Appendix 30 to Volume 3, Issue 2 of the 1988 British Intelligence in the Second World War, a substantially revised assessment of the Polish, French and British contributions to breaking the Enigma.

In 1987, the play "Breaking the Code" by Hugh Whitmore, about the life of Alan Turing, opened in London. The play is based on the 1983 book, "Alan Turing, the Enigma" by Andrew Hodges. Whitmore based the character in the play named Pat Smith, on Joan Clarke. Clarke co-operated with Andrew Hodges when he was researching and writing his book, but she chose not see Whitmore's play, declaring that: it would have been too painful.

She also assisted other historians studying war-time code breaking at Bletchley Park but due to continuing secrecy among cryptanalysts, the full extent of her accomplishments remains unknown.

On 4 September 1996, Joan Clarke Murray MBE died at her home in Headington.

She is remembered as "one of the really good cryptanalysts" of GCHQ who was liked and admired by colleagues throughout her long and dedicated career.

In this Interview, Actress Keira Knightly talks about Joan's unusual relationship with Turing, and explains how Joan can be seen to fit a feminist ideal.

You can read more about Joan and the other female codebreakers at Bletchley Park in Kerry Howard's excellent Book which you can buy at  
www.bletchleyparkresearch.co.uk/authors-researchers/kerry-howard/

Joan Clarke is portrayed by Keira Knightley in The Imitation Game, opposite Benedict Cumberbatch playing Alan Turing. However the film has been criticized for placing undue emphasis on the importance of the relationship between Turing and Clarke, with Andrew Hodges, a biographer of Turing, saying "the script built up the relationship with Joan much more than it actually was."

I believe Knightly has striven to give a faithful portrayal of Joan, but some of the facts may be a little blurry around the edges and some artistic license will always be used in movies.