Typex was a cipher machine developed by some chaps in the RAF in the 1930's, originally called "RAF Enigma with Type-X Attachments", since it was copied from the German Enigma. I think there was a legal patent battle, which evaporated in September 1939. Later it was called just Typex. Here are a couple of links, the second is quite detailed: Typex - Wikipedia, the free encyclopedia Typex There is not much on how it worked though. There were 5 wheels, or rotors. The three on the left operated exactly like the 3 wheels in the German Enigma. The two wheels on the right did not step but could be set to one of 26 positions as part of the machine key. The moving wheels used 'Enigma stepping' which included the double step feature; when a carry was generated from a faster wheel to a slower wheel the fast wheel would do an extra step. Current from the keyboard passed through the two stationary wheels, then through the three movable wheels to a fixed reflector which sent the signal back through the rotors to the output, which in this case was not a lampboard but a teleprinter which printed out the enciphered character on a paper tape. Since the machine was very similar to Enigma, it was used at Bletchley Park to decode Enigma messages once the keys had been broken. For this purpose the two stationary wheels were replaced with a plugboard to replicate the Enigma Stecker, and the rotors re-wired to the Enigma specification. Later a plugabble reflector was added and this can be seen in one of the photos - The Luftwaffe had added a pluggable reflector to some of their machines. (known as UKDW, or 'Uncle Dick') The Typex was much more secure than Enigma, since there were many more rotors available and the rotor cores could be removed and inserted in reverse to give a different wiring permutation. The rotors also had more than one stepping notch, unlike Enigma's single notch. A specification I have seen had 4 notches on each rotor. I found the last comment on the above link interesting. One of the BP cryptographers wanted to build a replica cipher machine with Meccano, Hitler defeated with Mecanno and also by a condom: "And how's this for improvisation? - John Roy describes a quick fix for Typex. "When we ran out of those springs used on the Typex tape reels, we used the Army issue condoms instead of the springs. A pair of scissors and a condom were kept close by. One a time, a piece of the condom was cut off and slipped over over the spring holders. The machine was placed in operation until the condom broke. The process was repeated until we could obtain proper springs. Army condoms were only slightly thinner than car inner tubes".