https://en.wikipedia.org/wiki/Joan_Clarke

She won a scholarship in 1936, to attend Newnham College, Cambridge, where she gained a double first degree in mathematics and was a Wrangler. She was denied a full degree, as Cambridge only awarded these to men until 1948.

In June 1940, Clarke was recruited by her former academic supervisor, Gordon Welchman, to the Government Code and Cypher School (GC&CS). She worked at Bletchley Park in the section known as Hut 8 and quickly became the only female practitioner of Banburismus, a cryptanalytic process developed by Alan Turing which reduced the need for bombes—electromechanical devices as used by British cryptologists Welchman and Turing to decipher German encrypted messages during World War II.

Although Clarke had the same position as her male coworkers, she was being paid less due to her gender. Clarke's first work promotion was to Linguist Grade which was designed to earn her extra money despite the fact that she did not speak another language. This promotion was a recognition of her workload and contributions to the team.

In the spring of 1941, Joan Clarke developed a close friendship with her Hut 8 colleague Alan Turing. Clarke and Turing had actually met previously to working at Bletchley Park, as Turing was a friend of her older brother. For a time, they became inseparable, Turing arranged their shifts so they could work together and they spent many of their leave days together. Soon after this blossoming friendship, Turing proposed marriage and Clarke accepted. However, devastatingly for Clarke, a few days after the proposal, Turing told her :-... to not count on it working out as he had homosexual tendencies.

Turing expected this to be the end of their affair, but Clarke was undeterred by his declaration, and their engagement continued. To understand her decision to continue with the engagement following his disclosure, it has to be made clear that during this period in history, marriage for many women, was considered a social duty and it was not necessary that marriage should correspond with sexual desires. Their engagement ended by mutual consent, because of Turing's belief that the marriage would be a failure because of his homosexuality