The Special Fish Report
Albert W. Small (December 1944)
Codes and Ciphers
TOP SECRET Special Fish Report Page 76
So a little piece of celluloid is used to mark down these columns that form
a good starting block, and the celluloid is slid back and forth to different
matches and partial matches, and the process is repeated until the 61-wheel
pattern has been obtained. The 37-wheel pattern then of course "falls out."
Messages in depth
The fundamental fish equations:
P + PSI' + X = Z
may also be expressed by the parametric equations:
(3) K = P + Z
(4) PSI' + X = K
both of which must usually be solved to read entirely any given message.
Newmanry and Testery both apply themselves to their solution.
Solution of (3) may be done by a process called "anagramming
messages in depth;" or by a process called "cribbing."
Solution of (4) is called "key breaking."
Recovery of key by anagramming messages in depth is well understood
by everyone. While the British are unconvinced of the ease of anagramming
two messages in depth in the Sturgeon machine, which Dr. Levine indicates
can be done without too much difficulty, in his paper on band transposition,
(wait till he gets over here!) they do it all the time on Tunny. Such a
worksheet follows. Procedure is to write out:
Message 1 - - - - - - - -
Message 2 - - - - - - - -
Difference - - - - - - -
If the difference is a 3, it probably came from 9 (or of course N) and if
a 5, from 9, and if an F, from N. In any case, they search through the