hope to be reading nearly all messages immediately about half way through the month.
Stab, as its name implies, was a higher grade key than the ordinary Offizier though it resembled it in many ways - the message was reencyphered in the same way and a similar list of settings existed, but the Stecker changed daily and the wheel order and Ringstellung were independent of the ordinary key and changed every 3 days.
There was very little Stab traffic at any time, in 1944 there may have been as many as 40 messages on all keys put together and in no previous year was there anything like this amount of traffic. We broke Dolphin Stab once in August 1944 off a long reencodement from Bonito, primarily with a view to discovering the nature of the key as it was only later that an example was pinched. There was far too little traffic for us to make any progress and in any case normal methods of Offizier attack were excluded by the changing wheel order. It was doubtless also the inconvenience of this change of wheel order which accounted for the very rare use of this cypher.
November 1944 saw the introduction of special keys for individual U Boats, and later for fortresses and individual flotillas. We had had warning of this development since June and it was presumably designed partly in the interests of external security partly also as a result of a desire to be able to communicate on confidential or highly operational matters with a single boat without the remainder being able to read the recyphered part of the message. Previous to this time messages of this type were preceded by an unenforceable order as to who might decode them or had to be encyphered by some complex "Captain's wife" method.
We expected that the Sonders would involve a change of Stecker and that the settings might or might not be the same as those for the Offizier; we thought it possible that the settings only would change. A less likely assumption was that the Sonder was some sort of Stichwort of the ordinary keys. All these assumptions were failed as exhaustively as possible but it was not until January that we obtained a certain reencodement from a "Captain's wife" message. We then discovered that both inner and outer settings were entirely different from those of the ordinary Shark or its Offizier.