Before revision: 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.
After revision: 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.