During World War II, Friedman was part of the team that broke the codes generated by the legendary German Enigma-machine. She also exposed a ring of German spies in South America. Her Cryptanalytic Unit eventually moved from Treasury and evolved into the modern Coast Guard Intelligence program. Only recently was her legacy fully appreciated when a journalist researched declassified papers to learn that she was pivotal in the German Enigma machine code-breaking as well as the Customs Prohibition operations.
A Life in Code: Pioneer Cryptanalyst Elizebeth Smith Friedman by G. Stewart Smith is well worth reading.