A few efforts (but very few) were made to break new days on the bombe with exclusively Short Signal menus.
JANUARY 1942 - NOVEMBER 1942.
After the end of 1941 (and even before it) virtually no Short Signals of any sort were sent except by U Boats (or in a few cases by U Boat port authorities). U Boats were divided between Norway - where there were a few boats talking on Dolphin, and the Atlantic and Mediterranean where Shark was used after Feb. 1st. Long E-bars became more and more infrequent as understanding and use of the new Kurzsignalheft increased.
This new B-bar book was introduced on January 1st, and during January there was a month's Atlantic U Boat traffic which came out on Dolphin keys. In this period there was an average of 4-5 B-bars daily. The indicator addition rule was discovered in the middle of the month and the probable number of indicators reduced to 316. Rodding efforts were concentrated on level starts, and signatures cribbed from acknowledgments and an incomplete signature list. Soon the cribbed signature VU produced 26 or so possible message settings for three B-bars on January 26 with indicator FTZ. One of these gave three decodes
CKKS KOKO NDSI YY
All these groups obeyed the law a.d = b-c and the sense of the acknowledgment tied up well with the meanings of such decode groups as could be found in the skeleton Feodor used for Rossaries. Moreover messages with the same Indicator on other days gave similar decodes. From this time the Indicator Table (Nr 1) and the codebook (based on Feodor) was systematically built up with the help of acknowledgments. The greatest stride in the compilation of Feodor was made when it was realised that the position groups gave grid square letters in addition to figures and that the table could be completed by interpolation with the use of a map.
After February 1st Shark keys were not available (except on three days) and work had to be confined to Dolphin B-bars: there were 4 in all February: and 2 in March. In June more boats became active in the Arctic, so that traffic was increased and in addition Norwegian stations started to send dummy B-bars (groups beginning with W). 50 Dolphin B-bars were sent in July, Oct., and Nov., and over 100 in Sept., and they proved useful for paired days and Ringstellung. By mid-October message settings corresponding to 130 indicators were known.