Born in Oxford, England as Ann Katharine Williamson, Mitchell attended secondary school at Headington School in Oxford, and then was awarded admission at the University of Oxford. She was one of only five women in her class, and she had chosen an unusual concentration. “My headmistress firmly told my parents that mathematics was not a ladylike subject” and shouldn’t take the offer from the prestigious university, she said. “However, my parents overruled her and I pursued my chosen path.” It’s a good thing: upon graduation in 1943 she was recruited by Bletchley Park to work on the intense and secret effort to break Germany’s Enigma code machine. She worked nine hours a day, six days a week, from fall 1943 to VE Day. For her first Christmas on the job she wrote in her journal, “Worked like the devil all day. Good fun.”
“The majority of the girls at Bletchley were part of a factory — a conveyor belt, really — to deal with the component parts of codebreaking,” says historian Tessa Dunlop, who wrote The Bletchley Girls, a book about the women who worked to break Germany’s codes. “But Ann was exceptional in the work she did finding the formula for the codebreaking machines. She was discreet, intelligent, and modest, and although she would never describe herself as a codebreaker, she was recruited for her mathematical ability.” After the war, she married (taking the name Mitchell), and worked as a marriage guidance counselor in Scotland. She then went back to school, earning her Master’s degree in Social Administration at the University of Edinburgh, and studied and wrote extensively on marriage breakup and divorce, especially how it affected children. Once the veil of secrecy about the Bletchley Park operation was lifted, Mitchell gave her oral history about her role, and was commemorated on the Codebreakers Wall at the Bletchley Park Museum. “Her experience was in many ways like that of Alan Turing and will long remain an inspiration to many,” said James Turing, the great-nephew of Alan Turing, who led the effort. Mitchell died in Edinburgh May 11, from Covid-19, at 97.