Cryptographic History of Work on the German Naval Enigma

been a wholly satisfactory solution of this difficulty. When entering self help a cribster saw a large block of traffic for an isolated day; what he really needed to see was a small block for several consecutive days. (4) Good though the service given to us by the Z watch was they could not be expected to spot everything and in fact some R.E's did slip past them. Moreover all these weaknesses were much more serious than they would have been in the past because on all keys we were working on a narrower margin.

25. The later arrangements can be summarized as follows. All traffic at all likely to carry to cribs was twice decoded the second copy going to the crib room. This was then skimmed through by the cribster on duty to see whether any significant changes had occurred. Normally he then passed it for entering to one of the girls calling her attention to anything new. If the key was in a difficult patch he might take over the entering himself for a few days to make certain that nothing was missed. On a key such as Plaice which always had a fair number of cribs but in which the situation was constantly changing and cribs appearing and disappearing all the time this procedure was essential, and on all keys we benefitted from it.

26. For the last two and a half years we always had a research cribster - first Ashcroft and then Pendered - who dealt with all keys on which we were permanently or temporarily stuck. The research cribster worked days and was able to examine the keys in a calmer atmosphere than that in which the shift workers had to maintain current breaking.

27. There were other activities for which the crib room was responsible such as Offizier, getting out paired days and menuing cribs for the M.R. but they were all subordinate to the main work and as they do not involve any point of general interest I shall not describe them further.


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