The scrambler unit was made up of rotors and a reflector. Each rotor had wiring within it that would change an input letter to some other letter. It was possible for a letter to not change when going through a rotor.

In our example, when "B" passed through the first rotor, it became, say, "Y". When "Y" passed through the second rotor, "Y" became, say, "S". When "S" passed through the third rotor, it was changed to, say, "N". From the third rotor, "N" went through the reflector, where it was changed to, say, "K".

The reflector was like the plugboard in that it transposed letters. If "N" was changed to "K", then "K" would be changed to "N". Unlike the plugboard, every letter got changed by the reflector. It was due to the reflector that the Enigma machine, in a given state, would only transpose letters. In other words, if the Enigma turned "A" into "B", it would turn "B" into "A". "A" would never be returned as "A" by the machine.

After leaving the reflector, the "K" passed through rotors in reverse order, changing the "K" to, say, "C", "C" to, say, "X", and "X" to, say, "U". Then the plugboard might change the letter. Let us suppose it doesn't in the case of "U". The circuit was then completed and the "U" was lit up on the Lamp Board. A letter would be changed as much as nine times by the machine.

Each time that a key was typed, the first rotor turned once. When the first rotor turned 26 times, the second rotor turned once. When the first turned 26x26 times, the second rotor turned 26 times, causing the third rotor to change once. (Note: This isn't completely accurate, due to the "double stepping" of the second rotor. For more information, read e-mail from Frode Weierud on the subject.)

To summarize, there were 26³ different rotor states for the three rotor machine, so there were 17576 states before the machine returned to its original state. The Germans had 6 different rotors, but only three rotors were used at one time. The three rotors were interchangable. This led to 6 x 17576 different rotor states. Later, the Germans used a four-rotor machine.

For Diagram of the Enigma, click here: Enigma Diagram