The US 6812 Division Bombe Report Eastcote 1944 Page 83

Tony Sale's Codes and Ciphers

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- 68 - TOP SECRET-T

The drums are mounted on a shaft extending through a commutator

mounted flush in the face of the bombe. 2 sets of keys are fitted to each
shaft, passing through it and extending beyond for about a sixteenth of an
inch on either side. As the drum is pushed onto the shaft the first set of
keys encountered consists or two pins, one behind the other which fit into
a keyway inside the drum and position the drum with respect to the shaft
in the direction of rotation. The second set of keys consists of one pin,
at right angles to the first set, which rides on a shoulder inside the
drum and determines the extent to which the drum may be pushed onto the
shaft.

The drums are locked in place by the latch mechanism on the face of

the drum which engages a circumferential groove near the end of the shaft.
After the drum has been attached to its shaft the combination of drum and
shaft may be set to any desired starting position because of a ratchet
mechanism interposed between the shaft and its drive mechanism. The setting
is prescribed by the menu, as for instance test menu 1 previously mentioned
specifies that the drums of the first enigma shall be set at Z Z S. This
means that the drums of one enigma (one fast drum with its associated
intermediate and slow drums) selected as enigma no.1 shall have its
fast drum set at Z, its intermediate at Z and its slow at S. The fast drum
is rotated until Z on its dial is set against the pointer attached to the
face of the bombe etc.

PLUGGING-UP BOMBE.

The connections indicated on the menu are made by a patching

arrangement of plugs and cords. The plug consists of a rubber plastic shell
4 1/4 inches long 1 inch deep and 1 1/2 inches wide from which protrude 26
flat prongs 3/8 inch long and 1/4 inch wide. These prongs are assembled in
pairs with insulating separators. The bottom of the plug is indicated by
metal strip inserted in the plug shell.

The jack consists of an element 3 1/2 inches long, 1 1/2 inches deep

and 1 inch wide mounted between uprights of 1 1/4 inch by 1 1/4 inch angle
iron. The angle iron is notched to receive guide prongs on the side of the
plug which position the plug with respect to the contacts of the jack. The
springs of the jack lay in a vertical plane and like the plug are assembled
in pairs. They are positioned and shaped to receive the prongs of the plug
and may be described as female prongs. These jacks are mounted in columns
on the rear of the bombe. Counting from the left as one faces the rear of
the bombe, the first, fourth and seventh columns contain the jacks
connected to the diagonal board. The second, fifth and eighth columns
contain the jacks serving the commons. The eighth column also contains the
input jacks. The third, sixth and ninth columns contain the jacks connected
to the enigmas. These latter jacks are associated in pairs, one jack of
which serves the input end and the other the output end of its enigma.

Assuming that test menu no. I is the menu to be plugged up the first

step in the procedure is to tie as many enigmas together by "commoning" (or
"coupling") jacks as is possible. This jack is a unit 5 inches long, 2 1/8
inches deep and 2 1/8 inches wide and consists of a jack element, described
above, in a special mounting on the rear of which is mounted a double ended
set of plug prongs extending in a vertical direction instead of in the
horizontal direction of a normal plug. This jack is inserted between the
"OUT" jack of a lower numbered enigma and the "IN" jack of a higher
numbered enigma be tied together. In the case of this menu 6 such jacks
would be inserted. Once inserted the jack is held in place by means of a
latching mechanism on the jack which grips extension plates on the angle
iron of the column. The two ends of the enigmas are thereby electrically
connected lead for lead and brought out to an auxiliary jack.

The next step in plugging up the bombe is to plug the enigmas to the

"common" jacks. The top set of "common" jacks is selected to connect to the
"input" because of its accessibility to the INPUT jacks. A patch is made
from the "comnoning" jack tying enigmas 4 and 5 to the bottom jack of this
set of "commons". Similarly the junction of enigmas 6 and 7 is patched to
the next to the bottom jack of this set of "commons". The junctions of
enigmas 1 and 2, and 3 and 4 are then patched to the second set of
commons. In addition the outer end of enigma 7 is patched to this set of
commons.


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