Enigma rotor details

Understanding the way the machine encrypts requires taking into account the current position of each rotor, the ring setting and its internal wiring.

No letter can map to itself, a cryptographic weakness caused by the same wires being used for forwards and backwards legs.

As an example, let us take rotor type I of Enigma I (see table below) without any ring setting offset.

With the rotors I, II and III (from left to right), wide B-reflector, all ring settings in A-position, and start position AAA, typing AAAAA will produce the encoded sequence BDZGO[citation needed].

With the rotors I, II, III (from left to right), wide B-reflector, all ring settings in B-position, and start position AAA, typing AAAAA will produce the encoded sequence EWTYX.

The surviving Swiss Air Force machines do not show any signs of modification.

Breaking Shark on 3-rotor bombes would have taken 50 to 100 times as long as an average Air Force or Army message.

Encoding mistakes by cipher clerks allowed the British to determine the wiring of the new reflector and its rotor.

Detail of rotor internal structure and wiring on display at the US National Cryptologic Museum
The scrambling action of the Enigma rotors shown for two consecutive letters — current is passed through the rotors, around the reflector, and back out through the rotors again. Note: The grayed-out lines represent other possible circuits within each rotor, which are hard-wired to contacts on each rotor.
The German Navy 4-rotor Enigma machine (M4) which was introduced for U-boat traffic on 1 February 1942.