 After graduation, she was recruited by the Army Signal Intelligence Service to work as a code breaker, at the recommendation of the Dean of Russell Sage.Caracristi was sent to Washington, D.C., she attended the cryptanalysis courses of William Friedman where puzzles were used to train cryptographers in the art of pattern recognition.During World War II, Caracristi's cryptography work was focused on deciphering the additive systems used by Japanese military forces and merchant fleet.