Cryptographic History of Work on the German Naval Enigma

later still. This meant that occasionally we wasted a lot of time - when a very bad W.O. had in fact been used - but on balance we saved a great deal.


27. In March Op. 20 G solved the "Bellatrix" Stichwort procedure using a Prisoner of War report. Shark for some time had had a series of Stichworts changing fortnightly or at even shorter intervals. This was an innocuous procedure except that as we did not know the relation of the "basic" W.O. (i.e. the W.O. appearing on the original key sheet) to that actually used, we could not use our wheel order rules to cut down bombe time. The Bellatrix series of Stichworts had a 4 figure number and the Stichwort itself was found by looking up the "log tangent" of this number in 5 figure log tables and using the last three figures as additive - the first was added to the wheel order the second to the ringstellung and the third to the stecker (a slight simplification of the original Stichwort procedure as described in Chap. 1 in which there was a different additive for each letter of the ringstellung).

28. An extraordinary type of message which appeared about now was the "Offizier's Wife" message in which the message setting was given by reference to various members of the crew e.g. the first letter might be described as "the second letter of the Christian name of the Chief Engineer's wife". These messages very seldom occurred and were even more seldom read, though we did break at least one. On one occasion Naval Section intelligence had a minor triumph as they knew the initials of one of the people involved and were thus able to give us one letter of the message setting.


29. In April Turtle repeated its March keys, an amiable gesture by the enemy which was to be repeated on other keys nearer the end of the war when communications became disorganized. Two new "throw-on" keys appeared at this time, Trumpeter and Bonito. Trumpeter was a small 3


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