Cryptographic History of Work on the German Naval Enigma

On the basis of this a menu would be made up and the Hut 8 duty officer (who might or might not be the short signal cribster) would decide whether to run it on the bombe or to wait for more signals to come in. While the final decision had to be taken by us it was of course greatly influenced by N.S. IV's opinion and in this connection Hut 8 owe a particular debt of gratitude to Jackson himself who worked all hours and showed a complete mastery of the facts and a soundness of judgment for which we all had the greatest respect.

31. From March 10th to May 20th there were U-boat patrol lines in the North and Central Atlantic; about 10 B bars a day were sent when no convoy was being attacked, many more when an operation was in progress - 70 were sent on one day when 3 conveys were being attacked simultaneously. Thus it was fairly easy to break in periods of activity and considerably harder in lulls. At the end of May the U-boats were withdrawn owing to heavy losses; new instructions (involving long R.E's) were plentiful, but B bars dropped to about 6 a day - mostly from returning boats in the Bay of Biscay reporting that they were 48 or 36 hours out of port. June was a period of declining usefulness of Short Signals and of increasing importance of R.E's. After June, the chief use of B bars was in breaking paired days.

32. The whole of the W W and B bar period was most interesting and contains several important lessons. First it shows the great importance of close cooperation - in the narrower field between all cryptographic sections and in the larger field between all sections - between everybody working in any way on a problem of this kind. In breaking W W's and B bars the following groups of people were involved (1) Hut 8 (2) the Met. section (under Archer) (3) The U-boat room (N.S.IV) (4) the Z watch (N.S.II, who translated the decodes and would see all the Shark short signal acknowledgments) (5) the D/F stations all over the world (6) Admiralty, providing position reports from our ships and sighting by Coastal Command - all this in addition to intercept stations, the bombe hut and Scarborough. The Hut 8 cryptographers sitting down on


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