Cryptographic History of Work on the German Naval Enigma

Chapter VII

September 1944 - May 1945

The Last Months

1. The last chapter dealt with a period of expansion but nevertheless one that was fundamentally stable and orderly - the expansion was part of a deliberate plan and the changes that took place were carefully calculated. We now come to a time when mingled with this planned change are a series of emergency measures designed to cope with problems arising suddenly through unexpected Allied advances. We were thus faced with a much more rapidly changing situation than ever before and all sorts of emergency procedures, which in some ways made the work harder, in some easier.

2. The exact date chosen to divide this chapter from the previous one is of course to some extent arbitrary, but September 1st is fairly satisfactory (1) because September was itself a pretty chaotic month in the cypher world (2) because September (mid August would be rather more accurate) marks the end of my own connection with Hut 8, the actual appointment of Mahon as head did not take place until November, but as I was in America from September to November he was in effective charge during the whole of the period covered by this chapter. This was an inevitable and highly desirable change; the technical work was now entirely cribbing, which I did not do and there was nothing like enough administrative work to justify my remaining. The administrative work in a section such as Hut 8 is in any case so intimately bound up with the technical details that it is (if possible) best handled by a technician.


3. In September, Bonito stopped throwing- on and all major keys now had to be broken on cribs - only Seahorse and Sunfish continued to use this discredited system (discredited by the Germans themselves since 1937), Sunfish being the sole key to retain it until the end of the war. Porpoise, Grampus, Trumpeter, Sunfish, Seahorse and Bonito were all in


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