Advanced Military Cryptography

A U.S. Army instructional text on cipher and code systems by the cryptologist William F. Friedman, reprinted by Aegean Park Press from Signal Corps training material. It picks up where an introductory volume leaves off, treating transposition and substitution systems at a more advanced level, with particular attention to systems that combine the two.

The text also covers cryptographs and their limitations, and code systems with an emphasis on enciphered codes. A separate section covers cipher machines: their function, the main types in use, and their relative advantages and disadvantages. The material began as Special Text No. 166 in the Army's extension-course curriculum. The Signal Corps revised it across several editions from the 1930s into the 1940s, and Aegean Park Press then issued this civilian reprint.

Friedman wrote it during his long tenure directing the Army's cryptologic training and research. He came to cryptology as a geneticist at George Fabyan's Riverbank Laboratories in Illinois. There he and his wife Elizebeth Smith Friedman turned a private research post into wartime code-breaking work. He founded and led the Army's Signal Intelligence Service starting in 1929, and later directed the team that broke the Japanese PURPLE cipher and helped design the SIGABA cipher machine.