An unusual Enigma variation. This is the only variant with four stepping wheels, however the fourth leftmost wheel is actually a reflector. The stepping mechanism is by gears which gives a simple cyclometric stepping sequence. A detailed description of this machine can be found in the paper: Hamer David H. 1999. G-312: An Abwehr Enigma. Cryptologia 24(1) 41-54.
The Abwehr Enigma Simulator can be downloaded Here. (Windows 3.1/95/98/NT4/2000/XP)