OP-20-G

OP-20-G
ActiveJuly 1, 1922 - July 10, 1946
Allegiance United States
Branch United States Navy
TypeCode and Signal Section
RoleSignals intelligence
Cryptanalysis
Garrison/HQNavy Department building, Washington, D.C.
Commanders
Notable
commanders
Captain Laurance Safford
Captain Joseph Rochefort
Captain John R. Redman

OP-20-G or "Office of Chief Of Naval Operations (OPNAV), 20th Division of the Office of Naval Communications, G Section / Communications Security", was the U.S. Navy's signals intelligence and cryptanalysis group during World War II. Its mission was to intercept, decrypt, and analyze naval communications from Japanese, German, and Italian navies. In addition OP-20-G also copied diplomatic messages of many foreign governments. The majority of the section's effort was directed towards Japan and included breaking the early Japanese "Blue" book fleet code. This was made possible by intercept and High Frequency Direction Finder (HFDF) sites in the Pacific, Atlantic, and continental U.S., as well as a Japanese telegraphic code school for radio operators in Washington, D.C.