Agnes Driscoll
The US Navy's leading cryptanalyst between the wars, who broke several Imperial Japanese Navy codes.
Agnes Meyer Driscoll (1889–1971) enlisted in 1918, the first year women were allowed to, and was assigned to the code section. After a spell working for Edward Hebern she came back and spent the 1920s and 30s as the Navy's top codebreaker — colleagues called her "Madame X".
She broke the Japanese navy's Red Book code, then the Blue Book in 1930, and made the first inroads into the machine the Americans named Orange. She also started work on JN-25 shortly before the war. That she is almost absent from popular history is partly because her best work stayed classified for decades, and partly because she never cared to be remembered.