Enigma Rotors Illustrating a Daily Configuration,
Courtesy of the National Security Agency Cryptologic Museum,
The Mariners' Museum photograph by Gregg Vicik
Enigma, Courtesy of the National Security Agency Cryptologic Museum, The Mariners' Museum photograph by Gregg Vicik
Codebreaking and cryptanalysis were difficult and extremely sensitive work that demanded total commitment. Constantly adapting to German alterations to the Enigma system, the Allied codebreakers understood, after painstaking efforts, the basic principles of operating the Enigma. Understanding German operating procedures was key to solving the Enigma system.
Encoding a message in naval Enigma required an extremely intricate series of steps. First, the machine must be configured to an elaborate series of predetermined settings listed in various codebooks. Using the codebooks, German signalsmen adjusted the "outer settings" of the Enigma by plugging wires into various ports on the plug-wire board in front of the typewriter keyboard. Before encrypting a message, an officer would check a list of daily settings to select the correct Enigma rotors. Aboard U-boats, the second watch officer (II W.O.) was responsible for adjusting the Enigma rotors to the proper daily configuration, establishing the "inner settings" of the machine. Each individual rotor featured internal circuitry connected to twenty-six electrical contacts representing alphabetical characters. Before typing a message, the signalsman would consult another codebook list to set the rotors to a predetermined daily starting position. For example, one daily configuration might be "T - A - M - W." By typing a letter on the keyboard, the rotors would turn. Thus, the electrical contacts on the rotors would produce an entirely different letter for each letter typedeven if the operator repeatedly typed the same letter.
With the "outer" and "inner" settings properly configured, U-boat signalsmen used codebooks to condense the length of the message text that was to be sent.
For example, in a message that reads:
My position is - EH - 56 - 61 - Am going along with supply boat - May - Have provisions for one week
the condensed code may read as follows:
KUKU = My position is
USIA = EH
MCSI = 56
MDCT = 61
VNUM = Am going along with supply boat
PPEE = May
HJIK = Have provisions for one week
Thus the message to be encrypted on Enigma would read as follows:
KUKU USIA MCSI MDCT VNUM PPEE HJIK
With the message properly condensed, the U-boat signalsman typed the text of a message on the Enigma keyboard to create an enciphered message. The alphabetical characters passed through the Enigma plug-wire array, turning the rotors to produce the enciphered characters on an illuminated panel. U-boat signalsmen then used standard Morse code to transmit the encrypted message in relative security to radio stations aboard other vessels or ashore. Once a message was transmitted, U-boat signalsman would reset the Enigma rotors to the proper daily configuration to encipher another message. To decipher messages accurately, the recipient had to set another Enigma machine to the exact plug and rotor settings of the original machine used to encrypt a given message.