The low traffic and experimental methods used by the German U Boats in June 1943 made B-bar cribbing difficult. After July B-bars cribs were still used from time to time, especially after the development of B-bars reporting attacks by British Aircraft. Emergency signals for use on these occasions were originally sent out in clear but on July 1943 instructions were received that all boats must carry UJKZ (a new group) and position cyphered on their machine in advance, and that the cyphered signals must be sent immediately an aircraft attack was threatened. Later boats were to describe the damage done in another signal of the form UJ.. and Position.
It was often possible to tie up suspected aircraft attacks with those reported by Coastal Command, and to accept the aircraft's estimate of the position though it was not always very accurate. In a striking case, a report of an aircraft attack was sent out uncyphered. The mistake was discovered and the identical signal sent out again cyphered 6 minutes later. This crib was spotted and used to break the day.
Even after B-bars were largely replaced by long reencodements as a means of breaking new keys, they were used extensively for getting out paired days by hand.
WWs after March 1943
The third edition of the WW book came into force at 0000 hours 10.3.43, and WWs increased in length by 4 letters. Subsequent Archery contained new information (Temperature difference between sea and air) in one place, and more detailed information in two others. It seemed certain that new indicator tables had been introduced, possibly giving 4-letter settings.
The first decode came from a WW at 0523/16 sent by U653 on the new book, but the old indicator table, the mistake being