Manual for the Solution of Military Ciphers

The first cipher manual issued by the U.S. Army, written by Captain Parker Hitt and originally printed by the Press of the Army Service Schools at Fort Leavenworth in 1916. This Aegean Park Press edition, part of its Cryptographic Series, reprints Hitt's plain, example-driven approach to solving unknown ciphers.

The text opens with Hitt's well-known statement of what solving a cipher demands: perseverance, careful method, intuition, and luck. From there it works through monoalphabetic and polyalphabetic substitution and simple transposition systems, using real intercepted cryptograms of the period. Solutions are explained step by step, with further problems left for the reader to work through.

Hitt was an Army Signal Corps officer and instructor at the Signal School at Fort Leavenworth when he wrote the manual, drawing on his own success solving Mexican revolutionary-era ciphers. His cylindrical cipher device, developed around the same period, was later adapted by Joseph Mauborgne into the M-94 strip cipher issued to the Army and Navy. His sliding-strip variant became the basis for the M-138-A. He served in France with the American Expeditionary Forces during World War I, running AEF coding and decoding, and retired a colonel. He is widely credited as the founder of systematic American military cryptology.