What does an Enigma machine do?

The Enigma machines were a series of electro-mechanical rotor cipher machines developed and used in the early- to mid-twentieth century to protect commercial, diplomatic and military communication. Enigma was invented by the German engineer Arthur Scherbius at the end of World War I. Early models were used commercially from the early 1920's, and adopted by military and government services of several countries, most notably Nazi Germany before and during World War II. Several different Enigma models were produced, but the German military models, having a plug board, were the most complex. Japanese and Italian models were also in use.

The Army Enigma machine used only the 26 alphabet characters. Punctuation was replaced with rare character combinations. A space was omitted or replaced with an X. The X was generally used as period or full-stop.

The effort to break the Enigma was not disclosed until the 1970's. Since then, interest in the Enigma machine has grown. Enigmas are on public display in museums around the world, and several are in the hands of private collectors and computer history enthusiasts.