In the general description of setting up a menu on a bombe, the
single input menu has been used as an example. There are several other
types of menus, a description of which follows.
Double Input - On some menus the crib produces several letters which are
not connected to the main menu by links and yet their menu is too strong
to be run as
a subsidiary to the main menu. In such a case both menus are plugged to
the same diagonal board and a double input used. The following is a sample
of such a menu:
This menu is numbered and plugged the same as for a single input except
that the second input patch is connected to Chain 2 or Auxiliary as the
case may be.
These menus can only be put on the bombe twice since there are only 4
chain circuits with associated inputs. In the older type machines a double
input plug board must be substituted for the single input. This changes
the association of wiring and the contacts of the sensing relays so that
the bombe will not stop unless there is an open circuit on both parts of
the menu. In the newer type machines the "double input" switch operated.
One letter (stecker) per chain must be read at each stop. On the older
type machines the letter for the auxiliary chain cannot be read on the
indicator and must be found by feeling the sensing relays for that chain.
On the new type machines this is read on the chain 2 portion of the
indicator. The search keys used for double input menus must be arranged to
cross search, that is the search key for the main menu has the same letter
designation as the input letter for the auxiliary chain and vice versa.
This practise has been adopted to give the best distribution of
current due to the association of the two search points through the
diagonal board. If this is not done you have more than one point on each
row of the diagonal board where you are applying potential and may obscure
the one o.c. point you are seeking.
5 Points of Difference in Plugging and Operating Double Input.
(1) Both menus plugged to the same diagonal board.
(2) Before starting be sure D.I.plugboard has been substituted for
S.I. board in old machines ,-D.1. key thrown on new machines,
(3) Be sure to "cross-search."
(4) Have technician find Auxiliary chain relay (indication) on old
(3) Record at least 2 relays per stop.
The checking of double input menus is somewhat different. In this
case you are supplied with two stecker letters ,one for the input of each
menu. Each menu is checked through independently. After deriving all
stecker letters, the two menus are evaluated as one to determine the type
of stop. It may be found in checking a female link that you have a boxing
stop,-you derive 4 stecker letters in going round the closure and have to
go round twice to obtain a closure. This is not a good stop since on the
enigma machine one letter can only have one stecker.