Update

In Compromise of State Department communications in WWII I made the following correction. I had written that the M-325 SIGFOY cipher machine was introduced into service in the second half of 1944, however that was not correct.

According to NARA - RG 59 - Purport Lists for the Department of State Decimal File 1910-1944 – microfilm 611 - 119.25 MC-325 the device was distributed to foreign posts in the second half of 1944 but the keylists were for the period January-June 1945. Thus the device could not have been used in 1944 by the State Department.

Information on State Department codes and ciphers

NARA has uploaded the microfilms containing entries on WWII era State Department codes and ciphers.

The entries dealing with cryptology are the 119.25.

Microfilm 444

Microfilm 445

Microfilm 611