Cryptologic History Calendar
1926: Enigma introduced into German Navy as Radio Key C.
Excerpt from Wikipedia:
The Reichsmarine was the first military branch to adopt Enigma. This version, named Funkschlüssel C ("Radio cipher C"), had been put into production by 1925 and was introduced into service in 1926.
The keyboard and lampboard contained 29 letters—A-Z, Ä, Ö and Ü—which were arranged alphabetically, as opposed to the QWERTZU ordering. The rotors had 28 contacts, with the letter X wired to bypass the rotors unencrypted.
Three rotors were chosen from a set of five and the reflector could be inserted in one of four different positions, denoted α, β, γ and δ. The machine was revised slightly in July 1933.