Cryptographic History of Work on the German Naval Enigma

on a "good fit" list as

ARX = AYR + 6.5 Octagram [i.e. 8 letter repeat] Certain (i.e. certainly right).

6.5 is the distance obtained by subtracting 5.6 from 11.11. This means (again ignoring double turn-over wheels) that X is 5 ahead of R in the end wheel alphabet and R is 6 (possibly 7) ahead of Y in the middle wheel alphabet. The third of the three entries is not good enough for immediate use but would be recorded and counted by the Big Room girls for future reference [Para. 17]. The difference between the first and third entries is that the initial letters of the message trigrams are the same for the third entry.

13. From the tetra catalogues and the "deciban-sheets" (the sheets on which all the results from end wheel comparisons are recorded by Big Room - so called because our scoring units were called decibans) all the good fits were collected and recorded together with their scores and odds. Here is the list as it might look [this is a far more favourable case than normal, in order to show simply how the method works]. A score 16/95 means 16 repeats including 6 consecutively out of an overlap of 95 letters between the messages - other scores are similarly interpreted.

and a number of weaker fits

*[9 letter repeat for benefit of non classical readers!]


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