Editing Enigma machine (section)

=== Plugboard ===
[[File:Enigma-plugboard.jpg|right|thumb|The plugboard (''Steckerbrett'') was positioned at the front of the machine, below the keys. When in use during World War II, there were ten connections. In this photograph, just two pairs of letters have been swapped (A↔J and S↔O).]]
The plugboard (''Steckerbrett'' in German) permitted variable wiring that could be reconfigured by the operator. It was introduced on German Army versions in 1928,<ref>Craig P. Bauer: ''Secret History&nbsp;– The Story of Cryptology''. CRC Press, Boca Raton 2013, p.&nbsp;248. ISBN 978-1-4665-6186-1.</ref> and was soon adopted by the ''[[Reichsmarine]]'' (German Navy). The plugboard contributed more cryptographic strength than an extra rotor, as it had 150 trillion possible settings (see below).<ref name="158,962,555,217,826,360,000">{{Cite news|last1=Van Manen|first1=Dirk-Jan|last2=Johan O. A.|first2=Robertsson|date=2016|title=Codes and Ciphers|work=Geo ExPro|url=https://geoexpro.com/codes-and-ciphers-part-i/|access-date=October 13, 2023}}</ref> Enigma without a plugboard (known as ''unsteckered Enigma'') could be solved relatively straightforwardly using hand methods; these techniques were generally defeated by the plugboard, driving Allied cryptanalysts to develop special machines to solve it.

A cable placed onto the plugboard connected letters in pairs; for example, ''E'' and ''Q'' might be a steckered pair. The effect was to swap those letters before and after the main rotor scrambling unit. For example, when an operator pressed ''E'', the signal was diverted to ''Q'' before entering the rotors. Up to 13 steckered pairs might be used at one time, although only 10 were normally used.

Current flowed from the keyboard through the plugboard, and proceeded to the entry-rotor or ''Eintrittswalze''. Each letter on the plugboard had two jacks. Inserting a plug disconnected the upper jack (from the keyboard) and the lower jack (to the entry-rotor) of that letter. The plug at the other end of the crosswired cable was inserted into another letter's jacks, thus switching the connections of the two letters.