cipher"; in a similar way to the more modern DRYAD and BATCO. The M-138-A was stronger because slips with new alphabets could be issued periodically, even by radio using more secure systems like SIGABA. Both were replaced by the M-209 mechanical rotor machine as these became available. See also Jefferson disk References External links DESCRIPTION OF CSP-488 a.k.a. M-94 Jerry Proc's page on the M-94 Pictures of the M-94 Instructions for the Cylindrical Cipher Device, U.S. Navy, 1926 Classical ciphers Encryption devices World War II military equipment of the United States Cryptographic hardware