A. The ENIGMA Machine
1. The Enigma is a mechanical device for performing a varying simple substitution on the successive letters of clear text of a message. It is so arranged that the substitution does not repeat (i.e. occurs a second time) until a consecutive stretch of about 17,000 letters has been encoded.
2. The machine is contained in a wooden box about a foot square and six inches deep. It consists of three WHEELS (Walzen) mounted between the CURRENT ENTRY DISC (Eintrittswalze) and REFLECTOR (Umkehrwalze), together with a KEYBOARD (Tastenbrett), LAMPBOARD (Lampenbrett), STECKER BOARD (Steckerbrett), BATTERY, and SWITCH (See Diagram 1). The lid of the box contains spare lamps, plugs, etc., and the whole is fitted with a handle for carrying.
Diagram 1. The Layout of the German 3 Wheel Enigma Machine.