in Dolphin - Shark re-encodements and the beginning of a steady flow of 4 wheel bombes again reduced the B bars to a subsidiary position from which they never emerged.
28. In the W W period Archer was our prop and standby and we received valuable but subsidiary assistance from N.S. IV. In the B bar months the position was reversed, N.S. IV under Edgar Jackson being absolutely essential to us while the chief value of Archer was to help us to break into the new W W book, a task which proved to be of only secondary importance. The tables in the new W W book were in fact broken very quickly indeed and by mid April were built up to a substantial extent quite sufficient for the W W's to have played a major part again had it not been that unfortunately the new indicator tables changed monthly. As there was not enough W W traffic to build up these tables quickly it was only towards the end of each month that W W's were of much use to us.
29. As the U-boat room, N.S. IV under Edgar Jackson were the authorities on the probable contents of B bars and they certainly gave us every possible help. Their function was to produce all available information that might help to determine which boat had sent which signal, the type of signal it might have sent and the exact position of the sender. The available sources of information [(1), (2) and (3) being the most important] were (1) Reported positions of British conveys (2) D/F bearings (3) Shark and Dolphin decodes especially Shark messages with instructions to send short signals (4) Positions of A/C sighting from Coastal Command and Aircraft carriers (5) RFP and Tina (Radio "finger printing" a method of identifying enemy wireless operators by individual peculiarities in transmission.)
30. Whichever cryptographer on duty was responsible for short signal cribbing would go over to the U-boat room when he had sufficient signals to give a chance of a bombe menu and everything would be thoroughly thrashed out between him and whoever was on duty in N.S. IV.
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