Bletchley Park, Britain's codebreaking headquarters, grew from a small country estate with a handful of eccentric academics to a vast operation employing roughly 10,000 people at its peak. Approximately 75% of the workforce were women, mostly from the Women's Royal Naval Service (Wrens), the Women's Auxiliary Air Force, and civilian volunteers.
These women operated the Bombe machines that cracked Enigma settings, ran the Colossus computers that broke the Lorenz cipher, performed the tedious but critical work of indexing and cross-referencing intercepted messages, and managed the vast administrative apparatus that supported the codebreakers.
All personnel signed the Official Secrets Act and were told that revealing their work could result in prosecution—and potentially death during wartime. The secrecy was maintained with extraordinary discipline: husbands and wives who both worked at Bletchley sometimes never knew the other was there, working in different huts on different shifts. Many workers did not learn the full significance of their contribution until the secret was partially declassified in 1974, nearly 30 years after the war ended.