The US 6812 Division Bombe Report Eastcote 1944 Page 39

Tony Sale's Codes and Ciphers

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- 34 - TOP SECRET-T

(c) the input is connected to the same common (Note: There is no
enigma plugged to this common.)
(d) insert a 2nd EEL plug into the bottom jack of the input common
(i.e. at D on example) The end plug Of the trailing daisy chain from
the 1st EEL plug is connected to the normal searching position on the
2nd plug, NOT THE INPUT LETTER, and any searching switch of a letter
off the menu is operated. The current is therefore put into the
enigmas in the usual way but returns to the input through the self
couple positions on the diagonal board. As soon as a straight is
called with a self-couple on it the current does not return from
that position and the differential relay concerned operates. THUS THE
RELAY CALLED WILL BE THE SELF COUPLE OF LETTER ON THE MENU, and the
stop will have to be checked from that point.
It will not be the coupling of the input letter.




Fig. 29. Method II, Plugging Single Self Steckered Menus.


Method III. (For double input menus)
The menu is plugged normally except: -

(a) plugging for the first input is as described above.
(b) SSS jack is plugged to a common which is plugged to second input.
(c) an EEL plug with all the letters off the menu plugged together is
inserted in this common.
(d) any letter off the menu is used for the searching position on the
2nd input.
(e) use the double input board.
(f) when a stop occurs, the relays indicated for the first input will
be the couples of the input letter, and those indicated on the second
will be the self couples.
(g) this method should always be used when there is an auxiliary
chain and the first input should be on the strongest chain.
Summary.
A stop may occur without a self-couple, if the relay on the 1st chain is
the same as the searching letter. Under this condition the other 25
relays will show and all the relays on the menu will show on the 2nd
input. If 25 relays show on the 1st input and not all those on the menu
show on the 2nd, those missing will be self-couples.
When only one input is used and the searching letter is self-coupled, all
relays on the menu except those self-coupled will come down.
It is possible for as many relays to be indicated as there are self-
couples.


Dummy Letter Menus. - This type of menu is used when it is desired to put
the menu on the bombe four times. The menu must consist of at least four
closures and not more than nine letters. It is plugged up 3 times normally
as a single input menu. For the 4th time no diagonal board is used. The 4th
chain does not cut out illegal



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