Enigma-M4

The Enigma-M4 (also called Schlüssel M, more precisely Schlüssel M Form M4) is a rotor key machine that was used for encrypted communication by the German Kriegsmarine during World War II from October 1941.

In contrast to the previously used Enigma-M3 and the Enigma I and the Enigma-G used by the German Secret services, the Enigma-M4 is characterized by four rollers (except for the entry roller and the reverse roller). This makes its encryption cryptographic significantly stronger than that of the other Enigma variants with only three rotors and therefore could not be broken by the Allies for a long time.