About 7,500 women worked in Bletchley Park, the central site for British cryptanalysts during World War II. Women constituted roughly 75% of the workforce there.^[1] While women were overwhelmingly under-represented in high-level work such as cryptanalysis, they were employed in large numbers in other important areas, including as operators of cryptographic and communications machinery, translators of Axis documents, traffic analysts, clerical workers, and more.^[2] Women made up the majority of Bletchley Park’s workforce, most enlisted in the Women’s Royal Naval Service, WRNS, nicknamed the Wrens.

The Wrens performed a vital role operating the computers used for code-breaking, including the Colossus and Bombe machines. Working around the clock in three 8 hour shifts, they were the beating heart of Bletchley Park.

Women were also involved in the construction of the machines, including doing the wiring and soldering to create each Colossus computer.

Bletchley Park was the central site for British cryptanalysis during World War II. It housed the Government Code and Cypher School (GC&CS), which regularly penetrated the secret communications of the Axis Powers – most importantly the German Enigma and Lorenz ciphers. According to Sir Harry Hinsley, the "Ultra" intelligence produced at Bletchley Park shortened the war by approximately two years.^[3] Bletchley Park is famous for the impact it had on the war and for the work performed there by scholars such as Alan Turing and Dilly Knox. This work, though secret until 1974, had a significant impact on the history of science and technology – in particular, the history of technology.^[4] In the past century, archivists and historians have increasingly emphasized the role of the women who worked in Bletchley Park.^[1][2][5][6]

In 1937, when the tensions in Europe and Asia were becoming apparent, the Chief of MI6, Admiral Hugh Sinclair, ordered GC&CS to begin preparing for a war-footing and to expand its staff numbers. These were to be "men of the professor type", primarily drawn from Oxford and, in particular, Cambridge universities.^[7] However, as the cryptanalytic work became increasingly mechanized, many more staff were needed.^[2] Women were first brought into Bletchley Park after being approached at university or because of trusted family connections; debutantes especially were prized, as they were considered the most trustworthy due to their upper class backgrounds.^[8][9] These "debs" performed mostly administrative and clerical work. However, the personnel needs of Bletchley Park continued to grow. The heads of Bletchley Park next looked for women who were linguists, mathematicians, and even crossword experts. The ability to do crosswords was explored in the interview of Jean Argles a codebreaker employed outside Bletchley Park. In 1942 the Daily Telegraph hosted a competition where a cryptic crossword was to be solved within 12 minutes. Winners were approached by the military and some were recruited to work at Bletchley Park, as these individuals were thought to have strong lateral thinking skills, important for codebreaking.^[10] The majority of these women came from middle-class backgrounds^[11] and some held degrees in mathematics, physics and engineering; they were given entry into STEM programs due to the lack of men, who had been sent to war.^[12]

By the end of 1944 in excess of 2,500 women were employed by GC&CS from the Women's Royal Naval Service (whose members were called "Wrens"); over 1,500 women were assigned from the Women's Auxiliary Air Force ("WAAFs") and approximately 400 came from the Auxiliary Territorial Service.^[13][14] Six out of ten women working in Bletchley Park were serving in the British Armed Forces.^[15] Many of those women were more interested in working on planes and ships, and never expected to work in a place such as Bletchley Park.

Women held numerous roles at Bletchley Park, ranging from administrators, index card compilers and dispatch riders, to a very few as code-breaking specialists. Initially many of the men in charge were skeptical that women would be able to operate the Bombe machines and the Colossus computers; in one section which employed women, including college graduates, the male section head opined that “women wouldn't like to do any intellectual work”.^[16] Gordon Preston persuaded Max Newman (who thought that the women would not care for the "intellectual effort") to authorise talks to the Wrens to explain their work mathematically, and the talks were very popular.^[17] Women in Bletchley Park soon proved themselves to be up to the task, as they performed good work in any position they held at Bletchley Park.^[18]

Though the initial focus of recruitment, particularly during the latter years of the inter-war period, focused primarily on male academics, there soon emerged an eclectic staff of "Boffins and Debs",^[19] which caused GC&CS to be whimsically dubbed the "Golf, Cheese and Chess Society".^[20] At the outbreak of the war Dilly Knox was the GC&CS's chief cryptanalyst and, as such, took a leading role in the work on the various Enigma networks. His team, which he staffed with women ("Dilly's girls"), included Margaret Rock and Mavis Lever, sometimes termed "Dilly's Fillies".^[21][22] During a September 1941 morale-boosting visit, Winston Churchill reportedly remarked to head of GC&CS Alastair Denniston: "I told you to leave no stone unturned to get staff, but I had no idea you had taken me so literally."^[23]

Women in World War II worked in many places that previously had been largely confined to men, such as industry and the military. Bletchley Park was unusual because the women there worked on demanding intellectual labour. One of the few directly comparable scenarios during the conflict was that American women recruited to do artillery ballistics calculations and program computers. These women "computers" used a differential analyzer in the basement of the Moore School of Electrical Engineering to speed up their calculations, though the machine required a mechanic to be totally accurate and the women often rechecked the calculations by hand.^[24]

This section tells the stories of a few selected women who worked in Bletchley Park.

There have been many efforts to commemorate the contribution of women in Bletchley Park; in particular, there has been a proliferation of online articles devoted to examining the role of women in Bletchley Park during the past 5 years. Due to the secrecy of Bletchley Park and the United Kingdom's Thirty-year rule, it wasn't until the 1974 publishing of The Ultra Secret by former RAF officer F. W. Winterbotham (who supervised the distribution of Ultra intelligence) that the wartime role of Bletchley Park began to be discussed, and only in 2009 did the British government award honours to its personnel.^[11] There have been recent efforts to get women who worked in Bletchley Park to meet up some 70 years after they last saw each other, as the women tended not to stay in touch with their coworkers after the war (due to the secret atmosphere back then).^[11][55] Women often didn't even know the names of the machines they had worked on until they read books about Bletchley Park released decades after WWII; families and friends usually had no idea what these women worked on during WWII.

Interviews of women who worked at Bletchley Park have them saying they enjoyed their time there due to doing interesting work and being around interesting people, as well as a sense that they were doing important work (although most never knew just how important their work ended up being, which reportedly shortened WWII by up to two years and saved millions of lives). Most women gave up their careers after they left Bletchley Park and got married; however, many of the full fledged female codebreakers (such as Joan Clarke) went on to have fruitful careers in cryptanalysis (bolstered by the good work they had done in Bletchley Park).^[11]

• List of women in Bletchley Park
• List of people associated with Bletchley Park
• United States Naval Computing Machine Laboratory, where some women recruited from WAVES worked as codebreakers (one notable such woman being Agnes Meyer Driscoll)