This was Sonder 702 - they were identified by numbers - and Sonder 224 was broken shortly afterwards on the same reencodements. No further messages in that month or the previous month could, however, be got out and we appeared to be up against a high-grade recyphering process with frequent changes of wheel order and Stecker.
The position was not actually quite as bad as it appeared. In April Sonder 161 was broken by the Americans on a reencodement from Sucker. This was the key to St. Nazaire which had already carried well over a hundred messages. It soon became apparent that the settings remained valid from month to month and that the wheel order and Stecker only changed 3 times in the month: the 26 settings never changed. Thus the same key was in force for the same 10 days of every month. 161 was soon completely broken.
With a key carrying as much traffic as 161 progress might well be rapid once an initial break had been obtained, but the average Sonder had only a few messages and the number of different Sonders was large. After a very long time indeed we might have broken enough Sonders and enough settings to have been making fairly rapid progress (a considerable amount of reencoding was inevitable) but from our experience elsewhere it is most unlikely, that the system would have remained unchanged for that length of time.
January 1942 passed peacefully enough but on February 1st Shark changed over to the 4 wheeled machines and was not broken again, with one exception, until December. This was a depressing period for us as clearly we had lost the most valuable part of the traffic and no form of cryptographic attack was available to us. I propose to leave the whole 4 wheeled machine problem until we reach the end of 1943 when we will review the evidence for its introduction, the bombe position, and the work that had been done on Shark in the meantime.
There is really very little to say about the next few months - or indeed as far as Dolphin is concerned for the next 18 months until autumn 1943 when we gave up Banburismus. We were a Section with one key which we were rapidly mastering completely; very soon it became usual to get out the Banburismus on the first day's traffic and there was normally no lack of cribs: in late 1942 the Bereich 7 weather reencodement from R.H.V. which I have already mentioned, started and the crib position became very secure. On July 1st 1942, the system of changing keys at midday rather than at midnight was introduced.