Plaice the Baltic key, was introduced on January 1st, 1944: it was a 3 wheel key. There was nothing new in the existence of an independent Baltic key. Under the German name of Laube the East Baltic, the part concerned primarily with Russian activities, had always used a separate key for most of the year but in 1941 and 1942 it had joined Dolphin from about December to March. Presumably it was considered that with the E. Baltic largely icebound and with very little activity it was not worth while to use a separate cypher. We used to look forward to Laube joining Dolphin as, although it had never been considered worth breaking when independent, it usually brought with it some useful cribs. By the end of December 1943 we were beginning to think that Laube was going to fail us and remain independent when to our great surprise all the West Baltic traffic broke off and joined Laube, or Potsdam as the Germans now called it.
Traffic on Plaice started in the region of 150 messages a day but rose steadily throughout the year. The Russian advances in 1945 produced an unprecedented spate of traffic, on March 13th 805 messages were registered. Between January 1944 and the end of the war Plaice was broken steadily, in all some 20 days remained unread.
In the early days we were extremely dependent on cribs from Werft, primarily the reencodement of Bereich 5 weather which did great service during the first six months. When Werft changed, as it did about once every 1 or 2 months, and no cribs were forthcoming Plaice would often be difficult but it was essential to break a few days to supply cribs for Werft. Once Werft was under way again, things were fairly easy. The existence of weather reencodements from Dolphin also made the position comparatively secure but these tended to be very difficult and must bombe time could be spent on them with comparatively little result. Fortunately Plaice was never on the list of operationally urgent keys, so delays in breaking could be accepted.
Later, in the summer of 1944, a group of operational U Boats was formed in the Baltic and proceeded to reencode Shark messages. This greatly improved the position of Plaice and also of Shark and Narwhal and for some months we were in the happy position where if we could get one of the 3 keys out reencodements should break the other 2. In January 1945 mention was made of a special key for these U Boats, a development which would have been a matter of great inconvenience to us, but the key was never introduced.
On February 1st 1944 Porpoise became a 4 wheel key. There had been very good evidence that this change was to take place on March 1st and preparations for tackling the new problem had to be greatly speeded up when we got the news right at the end of January. Grampus was unaffected, remaining a 3 wheel key.