A description of the German Enigma machine - Appendix F

A description of the German Enigma machine will show the complexity of the cipher.  The heart can be said to be three small rotors or wheels, hamburger-patty size, augmented by a few more rotors which could be interchanged with the first three.

            The basic three rotors fit on an axle or shaft between two stationary rotors, one of the stationary rotors being an entry point with the other being a reflector.  Each of the three rotatable rotors consisted of 26 plunger or spring-loaded contacts on one side of the rotor while on the other side were 26 flat contacts, all insulated from one another.  Inside the rotor the contacts were randomly connected to one another by insulated wires.  Movable rings were located on the rims of the rotors, providing a further encrypting arrangement.

            An important part of the machine was a small switch- or plug-board containing 26 jacks lettered A to Z.  Five to thirteen cords could be plugged into the board in a scheduled and changing arrangement, thus giving different electrical paths.

            A single letter, to be encrypted, started out by having a key pressed on the keyboard from where an electrical pulse proceeded through the plug-board, from there it flowed through the entry rotor, thence on a tortuous route through the three rotatable rotors to the reflector and a return tortuous route through the rotatable rotors and the entry rotor to an electric bulb with an inscribed but different letter that that typed.  It is to be noted that each time a key was pressed the right-hand rotor would advance a step.  When the rotor completed a full revolution the middle rotor rotated a step until eventually it completed its revolution and the third rotor would begin to rotate.

            Before encryption of a message it was necessary to set the keys.  First, the rings were arranged on the rotatable rotors.  The rotors were placed in the machine in a particular order for a set period of time.  Then the rotors were rotated to the basic daily setting whereby three assigned letters from an indicator list, example AJR, appeared in the apertures.  Next, three letters were picked at random, example TCA, and typed on the machine.  This would result in three encrypted letters, example LPN.  The rotors would now be rotated so that LPN appeared in the apertures.  From this position the message would be encrypted and processed into four letter groups.  The key indicator, TCA, is encrypted by using a separate table and changed into other letters that would appear as the first two groups of the message and repeated as the ending two groups.

            At the outbreak of war the Royal Air Force and Army were using a machine modelled on the Enigma that they called the Type X.  Unlike the Enigma it remained a secure system throughout the war.  It eventually came into use in the Canadian navy.  Coder Bill Sloan, of Etobicoke ON, remembers a Type X installed in the Code and Cypher Room in the Administration Building at Naval HQ in St. John’s Nfld.  Chief Petty Officer Dirks was the only operator and the only one allowed in the room.  The machine printed 5-letter groups onto tape.