Cryptographic History of Work on the German Naval Enigma

were able to read, to use the old system; the wheel order and the stecker being known, two or three messages from AFÄ were sufficient to determine the Grundstellung.

8. May 8th having been broken it was found to be on the same W.O. as April 30th and the intermediate days were duly broken and the Grunds found. Not knowing how the new indicator system worked, however, the Poles were unable to read the traffic on these days as they had done before and had to break out as many of the messages as they could individually. Knowing the stecker and wheel order this was not too difficult and about 15 messages were read on each day. They were unable from these messages to come to any more definite conclusion about the new indicating system than that it was probably some form of bigram substitution and at this stage the work was taken over by G.C.& C.S.

9. Looking back at the work done by the Poles and considering how little was known of the theory of machine cyphers when they started and how meagre was the mechanical equipment at their disposal one is filled with admiration for their work. They broke the complete wiring of the new machine, read the traffic currently by means of the "box-catalogues" until the indicating system changed, broke into the days following the change through cribbing and were beginning to discover how the new system worked when the work had to be handed over to us. Our subsequent success owed much to their early efforts.

Turing's Work.

(1) The Breaking of the New Indicating System Sept. - Dec. 1939.

10. When the war started probably only two people though that the Naval Enigma could be broken - Birch, the Head of German Naval Section and Turing, one of the leading Cambridge mathematicians who joined G.C & C.S. for the duration of the war. Birch thought it could be broken because it had to be broken and Turing thought it could be broken because it would be so interesting to break it. Whether or not


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