Cryptographic History of Work on the German Naval Enigma

day to day but repeated from month to month). This work had been started by Wylie and passed on by him to Ashcroft who did a great deal of patient and valuable work on all forms of short signals particularly W W's and B bars.

19. We were still however a long way from being able to use the W W's for breaking when, in October 1942, the Wetterkurz schluessel complete with indicator tables was captured in the Mediterranean from U-559. This pinch enabled us to read 8 days traffic in November, 25 in December, all January and February except Jan. 19/20th and February 28th and March 7th and 8th. On March 10th the book was changed and the great days of W W's were over.

20. Once the book had been captured things were fundamentally fairly plain sailing although there were a good many practical snags. Archer's section went onto 3 shifts as the operational importance of their work was of course tremendously increased by the pinch and constant and close liaison was maintained between us; we were always more than satisfied with the help they gave us and hope that they were equally happy about our cooperation.

21. As the whole subject of W W's is intrinsically very interesting in a general way and not particularly complicated technically it is worth giving an (imaginary but typical) example quoted by Ashcroft in a comprehensive write up of the subject.

22. (1) Instructions from control. "U-531 and U-668 are to send W W's between 0020 and 0400 tomorrow morning." Naval section (N.S. IV) estimate of positions

U-531 (signature LX) 53 x 33.

U-668 (signature PJ) 48 x 21.

[U-boats had two letter signatures known to us]

(2) Archery decodes spotted as being derived from W W reports :


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