Topic summary
Steckerbrett
Extracted from the Wikipedia article Enigma machine.
Plugboard
The plugboard (Steckerbrett in German) permitted variable wiring that could be reconfigured by the operator. It was introduced on German Army versions in 1928, 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). 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.