M-94 Cylinder

Jefferson described a wheel cipher in the 1790s, Bazeries built one in 1891, and the US Army issued it as the M-94 from 1922 to 1943: 25 disks with mixed alphabets, ordered by the key. A line of plaintext is set along one row and any other row sent. The disks here are those of the Army’s 1948 history; the key phrase rule and the worked example are FM 24-5’s.

• Army Security Agency, The History of Army Strip Cipher Devices (SRH-366, 1948), fig. 3
• FM 24-5, Basic Field Manual: Signal Communication (1942), pars. 55–61