Cryptographic History of Work on the German Naval Enigma

sometimes not until quite late on. [When we had numerous separate keys later in the war, the Offiziers of less important keys were often unbroken but OYSTER and LIMPET the Offiziers for DOLPHIN and SHARK were regularly read]. We had two standard methods of breaking which are perhaps worth mentioning. One was the "E. S. Programme" which was a routine message giving recognition signals and appeared regularly in Limpet and Oyster (the first break was made on this); the other was though use of "FORT"s, reminiscent of the Poles' early efforts - on the small Offizier traffic it was easy to spot when one message was a continuation of another in which case one tried FORT followed by the time of origin as a crib. This was very laborious as the Germans buried the FORT in the message and it might be necessary to try 100 positions - this was practicable because there was only one W.O. to test.

15. The only other event in October was a temporary panic over SHARK. When October 3rd and 4th were broken the U-boat traffic failed to decypher in the normal way. Using an R.E from Werft (a hand cypher used by small ships in Home Waters, mainly in the Baltic) a message was got out and it was found that Shark was using an entirely different Grundstellung from Dolphin. Since April it had been using as Grund the reverse of the Dolphin Grund i.e. if Dolphin had Grund ABC, Shark would have Grund CBA; this was a trivial difference and the new change was also of very minor importance in itself but it was an ominous sign of things to come.

16. In November Mahon, later to be head of the section, joined the crib room, bringing its strength up to four. Wylie, Noskwith, Mahon and six girls acting as assistants manned the three shifts while Ashcroft worked on his own chiefly on short signals (later an invaluable means of breaking Shark) and on "dummyismus" - keeping the dummy statistics up to date. This was a satisfactory arrangement, as Ashcroft was excellent at individual work which he could take in this own time, while the others were better shift workers.


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