an expert permanently at work analysing the weaknesses of the machine does on the other hand little credit to their technical ability. The crib chasers gave us a fairly bad time, especially in the areas nearer home where the cyphers were better organized, and by March 1945 Dolphin - a large key of some 400 messages a day - had been rendered almost cribless and we might have failed to read some of the last days had we not captured the Hackle keys which kept us supplied with re-encodements.
Cribs in the early days were largely weather messages. A very large amount of weather was sent in enigma and it was obvious that it was regarded as of first importance. In 1941 weather cribs from the Channel ports were our principal standby and WEWA BOULOGNE and WEWA CHERBOURG were trusty friends. The security officers pounced on this habit of announcing internally from whom the weather originated one day during the late autumn, but first class cribs of a rather shorter variety continued to come regularly at the beginnings and ends of messages. Rather curiously this habit of signing weather messages at the end never caught on elsewhere and after the death of the Channel weather cribs in spring 1942 we never again had cribs at the ends of messages. This was, on the whole, convenient as a message always finished with a complete 4 letter group (irrespective of the number of letters in the plain text, dummy letters being added at the end) so that an end crib could be written in 4 different places and one had to be fortunate with the crashing out for a single really good shot to be available.
The reprimand to the Channel weather stations for insecurity in April 1942 is something of a landmark as the Channel cribs never recovered except for the remarkable run of ZUSTANDOSTWAERTIGERKANAL during the summer of the same year. Henceforth they omitted such lengthy statements as WETTERZUSTANDEINSACHTNULNULUHR and satisfied themselves with a terse NANTESBISBIARRITZ buried somewhere in the middle of the message. This habit of burying sign-offs was an almost completely effective anti-crib measure and became more and more widespread as time went on.
Weather cribs in Norway and the Baltic were useful for a long time and in the Mediterranean for even longer, but there can be little doubt that the security services were weather conscious and one after another cribs of this type disappeared. They were replaced by other cribs of a type which generally required more finding - some were situation reports of a fairly obviously routine nature, others were much more elusive. For instance, when looking through a days traffic one was not likely to be struck immediately by a message from Alderney to Seekommandant Kanalinseln which said FEUER BRANNTEN WIE BEFOHLEN but it was in fact a daily confirmation that various lights had been