William Frederick Friedman was a US Army cryptographer who ran the research division of the Army's Signal Intelligence Service (SIS) in the 1930s, and parts of its follow-on services into the 1950s. In 1940, subordinates of his led by Frank Rowlett broke Japan's PURPLE cipher, thus disclosing Japanese diplomatic secrets before America's entrance into World War II.

Abraham Sinkov was a US cryptanalyst. An early employee of the U.S. Army's Signal Intelligence Service, he held several leadership positions during World War II, transitioning to the new National Security Agency after the war, where he became a deputy director. After retiring in 1962, he taught mathematics at Arizona State University.