The US 6812 Division Bombe Report Eastcote 1944 Page 37

Tony Sale's Codes and Ciphers

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- 32 - TOP SECRET-T

in one of the 26, the chances of it being that one is 25-i. By suppressing
the others we arrive at the same condition we would have if we added a
closure. The possible number of stops per wheel order is 26x26x26x26.
Therefore with four self steckers we could run a menu which would average
only 1 stop per wheel order. The searching point is usually put at some
letter off the menu. The menu is plugged by the use of EEL plugs. An EEL
plug is one in which the wires from the plug contacts are brought out to a
plug board mounted on the plug and used with a "daisy chain". A "daisy
chain" is a cord with 25 single conductor plugs connected to each other to
permit short circuiting 25 of the letters. The plug is always inserted with
the metal plate on the bottom and under that condition the plug board is
designated A/B C/D --- Y/Z. In plugging the above menu, the inner end of
enigma 1 would be patched to the first "common" jacks. An EEL plug with A
left open is plugged into these common jacks. The plugging is similar for
all other letters except that a different letter is left open on the EEL
plug. On a completely self steckered menu you do not need a diagonal board.
The bombe runs until it reaches a wheel order and ringstellung where all
the above letters are self steckered. To make a check stop pull out the EEL
plug furthest away from the input.

If there is a menu with one self stecker only, choose that as the

input provided it is not a straggler. This gives a quick check that the
correct relay is coming up. For example, if ,as below, the input is at B,
only the B relay should appear on a stop.



A bombe stops when there is an open circuit on the input and, under normal
conditions, one to three relays come up. If, with the input at B as ind-
cated , relay F comes up there is an open circuit at F and current on the
remaining positions. But we do not want to stop at F for this menu. So we
short circuit all other letters except B which puts current on F and
rejects the stop. For this example we plug the bombe normally and then in
the common to which B is connected plug an EEL plug with the B point
isolated,

Where a self steckered letter is used, commons must be employed

except in extreme cases, such as in the first example where the EEL plugs
can be plugged directly into the enigmas at A,C,D,E and F, using a common
only at B(the input). The menu then becomes a Dummy Letter Menu in which
contradictions are not permissible and each letter must be self steckered.

Prohibitive or Mandatory Steckered Menus. - This type of menu is similar to
the self steckered menu except that some of the letters are specified to be
coupled to letters other than themselves. For instance:



In this case EEL plugs are used for all the letters and arranged to couple
the letters as indicated. The EEL plug at F will have A isolated , that at
W will have R open and that at D will have Q isolated. P, of course is self
steckered and it's EEL plug will have P open.


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