Anticipating enemy attempts to intercept radio signals, the German navy developed codes and cipher machines to cloak the text of radio messages. Transmitted in standard Morse, German naval signalsmen used the Spruchschlüsselmaschine-M (cipher machine-naval) to encrypt the text of their radio messages. Best known by its commercial name "Enigma," this innovative cipher machine was a uniquely complex device. Typing a given alphabetical character on the Enigma typewriter keyboard, subjected that letter to an extremely complicated electromechanical process leading from the keyboard input, out through the plug and wire connections below the keyboard, and into the rotating wheels at the top of the machine. As the rotors turned, the electrical circuit connections changed. Once a given electronic letter was processed through the rotating wheels, the character was reflected back through the rotors. The encrypted Enigma letter would then appear on the lighted output panel between the rotors and the keyboard. Thus, when one presses the letter "A," the letter is processed through the Enigma and may appear as the letter "Z" on the output panel. Pressing the letter "A" again would once again process the letter through the Enigma, but as the rotors turned, the electrical circuit would change. As a result, the letter "A" may appear as any one of the twenty-six letters in the alphabet.
The complexity of the Enigma system convinced ranking German naval leaders that the cipher was essentially unsolvable by enemy cryptanalysts. For the first years of the war, the German military was primarily equipped with the three-rotor model (M3) Enigma, which was capable of producing more than 150 thousand trillion variations of a single character. Shortly after German forces seized Poland and France, the German navy adopted a more complex version of Enigma. In 1941, selected German capital ships were equipped with a four-rotor model (M4) Enigma. Featuring an additional rotor port, the M4 Enigma vastly increased the ratio of possibilities for enciphering alphabetical characters. However, the improved M4 Enigma was only available on a highly restricted basis, and the U-boat fleet continued using the standard M3 version throughout 1941. As U-boat operations intensified in the North Atlantic, extending to African and American waters, U-boat signalsmen were equipped with the improved M4 Enigmas by February 1942. Further complicating the Enigma cipher, the fourth rotor port in the M4 models accommodated the improved "Greek" rotors known as BETA and GAMMA , which had a unique circuitry and were different from the standard issue Enigma rotors already in use. Page 1 of 2 | Next >>
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