Mary Louise Prather joined the Signal Intelligence Service in
1938 and worked in the clerical field. After a few years, she
was promoted to Chief of the Stenographic
Section. Her duties expanded to include logging cipher messages
and preparing the office's decrypted messages for distribution.
Due to her careful logging, she identified a relationship between
two Japanese messages that led to the recovery of a new code.
During WWII, she was promoted to Administrative Assistant and Personnel Officer for the General Cryptographic Branch. In 1946, she received the Commendation for Meritorious Civilian Service. Through the 1950s, she held a variety of positions increasing in responsibility until she was named the chief of the Soviet Information Division in 1960. In 1969, she received the Meritorious Civilian Service Award.