The German Signals Service failed, however, lamentably in its functions (though Werft and R.H.V. are not, of course, low grade cyphers) and its cyphers were most extensively read. In later years we should never have been able to continue regular breaking on a large number of keys if it had not been for the steady flow of reencodements and their complete failure to master the reencodement problem was without doubt one of the biggest blunders the German Security Service made.
AUGUST - NOVEMBER 1941.
During the Autumn of 1941 the outlook became steadily brighter. In August there were 6 bombes in action and we had the bigram tables without which Banburismus was impossible.
The results speak for themselves. All August was broken except 1 - 4, 24 - 25, all September, and all October except 3 - 4 and 12 - 13. From October 14th, 1941 Dolphin was broken consistently until March 7th, 1945.
During these months methods of Banburismus and Cribbing improved considerably and the situation gradually developed that stability which can only arise from a long period of regular breaking.
Early in October, on the 3rd, 4th, or 5th, we were mystified by the failure of the U Boat traffic to decode when Dolphin for the day had been broken. The situation was saved by a Werft crib, one of Werft’s earliest triumphs, and it transpired that the key was the same as for the rest of the traffic except for the Grundstellung, which was entirely different. This was a further development of the innovation of April when the U Boats started to use a Grundstellung which was the reverse of that used by surface craft. This new development made very little difference except that it delayed slightly the reading of the U Boat, traffic.
November 29th brought the first real crisis in the form of a change of bigram tables and K book. 6 months earlier this would have beaten us, but we now knew enough about cribs to be able to break the traffic without Banburismus if sufficient bombes were available and there were now 12 bombes in action. Rather curiously we thought it worth while to indulge in the luxury of a Freeborn catalogue of fits in the hope of being