The US 6812 Division Bombe Report Eastcote 1944 Page 11

Tony Sale's Codes and Ciphers

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- 6 - TOP SECRET-T


The bombe is designed to try simultaneously 26 steckers of the

input letter on as many enigmas as there are possible pairs leading
to steckers(indicated by the crib). The test of 26 possible steckers
is made at each position of the wheels. The wheels are advanced
through 17,576 positions in each run. Each enigma has the same wheel
order and is set to a starting position which bears the same relation
to ZZZ that the actual machine bore to its "starting point".

The DIAGONAL BOARD is made up of 26 jacks of 26 contacts

each, representing all possible steckering of each letter to itself
and each other letter. The purpose of the board is to ensure that all
steckers obtained are legal(good), conforming to the characteristics
of the German machine and that no illegal contradictions (bad
steckers) are shown. A miniature diagram for 6 letters is shown.




Fig. 6. Partial Diagonal Board


The diagonal board is arranged so that all reciprocals are
permanently wired together, i.e. if A is connected to f then F is
connected to a. When encoding or decoding on the German machine
current is present on only one out of 26 possible circuits.
Conversely a correct stecker will be obtained on the bombe when the
diagonal board has only one set of contacts (a "straight") without
current - current is on all other 25 circuits. The use of the
diagonal board may be understood from the following menu:




Fig. 7. Sample Menu.

With such a menu set up on a bombe the following paths through the
enigmas were found by test to exist when the bombe stopped.


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