War Diaries for Bismarck and Prinz Eugen

[Vic Dale]

Hi Tommy old friend.

It came to me in a dream - well more in the waking state after a good sleep.

The Encryption Code could not possibly be sent in the encrypted signal, because it could never be seen until the signal was decoded. The law of logic intervenes heavily here - finally. The Encryption code would never be sent "in the clear" either as this would give a beautiful crib to the Cryptanalysts at Bletchley Park.

The three letter Encryption Code for each signal is established by the time it is sent and that is the reason for the Uhrzeitgruppen - the time of send. Each machine is set up for the day and the encryption code, plug settings and selected wheel settings are applied. At Group West they would read the send time (UZ) and set the encryption code before deciphering. If the signal was a ship to ship message, the same would be done in the receiving ship. If the signal came from a ship in a different time zone that would be shown in the clear with the time-set mark, A B,C .......Z

All signals must have the time (Uhrzeitgruppen) and the time set (A,B,C...Z) appended in the clear, for example "0700 (B)" so that part can be read prior to decryption. The (B) denotes Bravo Time, or (Z) Zulu Time etc. The Uhrzeitgruppe has to be the time of send.

[tommy303]

It is true that setting books, consisting of sheets for each month of the year, but the proceedure was a bit more complex. These had for each day the rotors and reflector to be used, the rotor ring setting positions, and the wire plug settings; the possible rotor settings keys were listed in the Kenngruppenbuch which had sets of triagrams that could be used on each particular day. The operator would set up the M3 Enigma according to the settings for the day. He would then select two of the letter triagrams from the Kenngruppen list. The first was the start position for the rotors used to encode the actual message key. He then typed in the second to to obtain the encrypted message key.

The operator then added a random dummy letter to the start of the first triagram and a dummy letter at the end of the second. Together, these two formed the message indicator. This was further encrypted by use of a double letter conversion table unique to a specific day. The resulting two four letter groups were placed at the start of the message and repeated at the end.

The decoder would take the two four letter groups and reverse the process using the double letter conversion table to obtain the correct rotor start positions and decrypt the message key after deleting the dummy letter at the start of the first group and the dummy letter at the end of the second. With that, he could then set the rotors of his machine to the correct message key and decode the message. I hope that makes a little sense.

All in all, the naval proceedure was both quite different and considerably more complex than the army/luftwaffe proceedures.