increase almost to the very end, the record intercept being 2,133 messages on March 12th 1945. At the same time the number of keys in use also increased and whereas in 1941 we had one main key to deal with, Dolphin, plus its Offizier, Oyster (all our keys had the names of sea fishes, the Offiziers as the hardest to break being shellfish) there were about 20 keys in use by the end of the war, most of which we were either breaking regularly or had broken often enough to see that they were not worth further work.
58. This was the background of our problem. The story of Hut 8 in the next chapter is an account of the struggle first to break into the system at all and then to keep pace with the steadily increasing difficulty of the problem caused by the enemy measures (1) to increase the inherent security of the machine (replacement of the 3 wheel by the 4 wheel machine) (2) to improve the use of the machine (abandonment of "throw-on" systems of indication and attempt at suppression of cribs from routine messages) (3) to split their traffic amongst as many different keys as possible.