Another remarkable series of reencodements linked Dolphin and Sucker from November 1944 until the end of the war. In this case it was a weather message from the Hook of Holland which was repeated in almost identical form in the 2 cyphers. This crib was responsible for our consistently good results in Dolphin during the last months of the war.
Another weather reencodement of considerable interest was that of BEREICHDORA - an area in the Skagerrak and West Baltic of interest to Plaice and Dolphin. This message originated from Swinemunde on Plaice and was repeated on Dolphin by one of a variety of stations, in accordance with a complicated programme. The repeating station was responsible for hatting the original and for sending it out on the Dolphin frequencies; normally the repeating station encyphered it twice with the text in a different order and sent it out as 2 independent messages. Security precautions were in fact extremely strictly enforced. However, the original Plaice message always set out its observations in the same order - wind - cloud - visibility - sea - and it was possible to take the Dolphin message and reshuffle it into its original order. BEREICHDORA remained far too tricky to be a high grade crib but it was used regularly and quite successfully when nothing better was available: there were several periods when it was in fact our only crib into Plaice. The final refinement of discovering the principle on which the Plaice was hatted and using it for breaking Dolphin remained beyond our powers.
The remaining and most curious type of reencodement was between one days traffic and another on the same cypher. These reencodements were found largely in the Baltic where a series of BELEHRUNGSFUNKSPRUECHE were sent to the training U Boats and were repeated frequently for some weeks. There was no law as to when these might be retransmitted but, presumably because their content was a didactic value and the decyphering of them good practice, they occurred at one period fairly frequently and could often be identified by their exceptional length. Dolphin also produced one crib of this type, perhaps the longest lived of all our cribs and one which would have broken Dolphin daily had it been possible to intercept the message satisfactorily. It was a statement of areas off North Norway in which anti-submarine activities were to be allowed during the next 24 hours and, while the areas did indeed sometimes change, much more often they remained the same and the message of the day before supplied the crib for the message of the new day.
Commander Denniston wrote:
"The German Signal Service will do its best to prevent compromise of Enigma by inferior low-grade cyphers.....the Germans do not intend their cyphers to be read."