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Report #F 46 (continued)
placed on the crib tape, at the beginning and end of each blank stretch,
to stop the machine from counting and to start it again. Another symbol,
after the final stretch, causes the scores to be recorded.. It is
apparent, however, that this method requires tremendously long tapes so
that the first practical simplification is to use only a few multiples
of 31. However a much easier method which avoids the expenditure of a
lot of preliminary time in making tapes is to use the double Robinson
machine with 2Z2 tapes and 2 DeltaP2 + P5two back tapes. Z2 can be used
instead of DeltaZ2 because the machine can do the differencing. Separate
runs are then made for intervals 31, 62, etc. and the high scores compared.
This saves preparation time but takes a little longer to check and evaluate
12. It would seem that location of cribs by this method could very
easily be accomplished with IC equiprient. If equipment is used which will
not record scores the method described at the beginning of paragraph 11
is probably the best. Plates present the usual drawbacks but with the
film machine the testing would be much more rapid than on the Robinson.
The preparatory work is, of course, substantial.
13. The crib on which Jellyfish was broken by this method was from
Bream and was about 1600 letters long. Both messages were from Berlin.
The crib turned out to have been fairly correct for about two-thirds of
its length but the balance was all wrong. The message through which it
was dragged was about 2200 letters long so that approximately 600 positions
had to be tried.
14. Enclosed is description, prepared by Maj. Tester's section,
covering the method (mentioned in Report #F 43) used to recover wheel
patterns from Stickleback key. Apparently the method is not as new as I
had been informed.
15. Some Sturgeon type traffic of July 1943 has finally been read
and as a result the machine, as then used, has been reconstructed. The
link read was Halibut. It consisted of practice messages and is no longer
passing traffic. It is believed that the current permuted Fish traffic is
sent on the same type or machine but with an auto-key element added. The
Halibut machine has 10 wheels with periods ranging from 47 to 73. The
patterns are fixed and are the same as wheels previously solved. 5 of the
wheels act in a combining capacity (the British call these subtractor
wheels and designate the key they produce by capital sigma,Note I will use
£) and the other 5 act as permuters. The permutation key is designated pi.
The enciphering equation is written Z =pi(P + £) which indicates that
combination takes place before permutation. In deciphering. the permutation
is the first step and the equation is P = pi^(-1) + £ . Each wheel can act in
any capacity so there are 101 wheel orders.
16. The permutation consists of a series of exchanges between