During the second world war, a major strategic challenge of the army was to be able to decode the messages that the opponent sent to his troops. The “code breakers” were mostly women.
US code breakers
Most of the Army’s and Navy’s code-breaking force was female. There were more than 10 000.
More on NSA code breakers:
Who were the Code Girls?, by Liza Mundy (Youtube)
Sharing the Burden: Women in Cryptology during World War II, by Jennifer Wilcox (PDF)
Among them was Agnes Driscoll.
She reconstituted several Japanese books (called “cyphers”) used to encrypt messages.
Agnes Driscoll decoded the Red Book Code in the 1920s, the Blue Book Code in 1930, and, in 1940, she made critical inroads into JN-25, the Japanese fleet’s operational code, which the U.S. Navy exploited after the attack on Pearl Harbor for the rest of the Pacific War. In early 1935, Mrs. Driscoll led the attack on the Japanese M-1 cipher machine (also known to the U.S. as the ORANGE machine), used to encrypt the messages of Japanese naval attaches around the world.
Source on NSA:
Agnes Meyer Driscoll, Hall of Honor
The Neglected Giant: Agnes Meyer Driscoll
UK code breakers
In January 1945, some 10,000 personnel were working at Bletchley and its outstations. About three-quarters of these were women.
More on Bletchley Park’s code-breakers: Who were the Codebreakers?
One of those woman was Joan Elisabeth Lowther Murray (born Clark, 1917 – 1996).
Her role in the Enigma project that decrypted Nazi Germany’s secret communications earned her awards and citations, such as appointment as a Member of the Order of the British Empire (MBE), in 1946.
She appears in the movie on Alan Turing : The Imitation Game.
Source: Joan Clarke, the woman who cracked Enigma cyphers with Alan Turing, by Joe Miller, 2014