spread to other keys in the near future. Believing there to be 9 bigram tables we had estimated that it would take 2 months before we could return to a normal operational basis and this estimate was made on the assumption that we should still know enough about the traffic to produce cribs and break days on assumption that was admittedly somewhat optimistic. It is, I think, possible that we should not have survived this bigram table change but I do not agree with the view that the universal use of Grund tables would in itself have been a mortal blow. It would probably have been necessary to capture the bigram tables and after that the Grund tables would have been merely a nuisance, a very great nuisance certainly but one which would have been overcome by great increases in the available equipment for breaking messages.
At the end of April and beginning of May the position from the point of view of the cribster, who thrives on a stable situation, became more and more depressing and it was certainly more by luck than good management that we made a start on all keys in May and broke Dolphin, Plaice and Shark right up to the surrender.
Our success was to a large extent due to the series of manifestoes put out by the German government which were reencoded on all keys. Security at this stage became very bad and there were several reencodements from plain language, the most remarkable being the repetition in the High Command Communique of Doenitz' final Order of the Day to his U Boats.