The US 6812 Division Bombe Report Eastcote 1944 Page 84

Tony Sale's Codes and Ciphers

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- 69 - TOP SECRET-T
Again the junction of enigmas 2 and 3, and 5 and 6 are patched to the third
set of "commons". The inner end of enigma 1 is also brought to this set.
Now returning to the top set of commons a patch is made to letter E of the
diagonal board and another patch to INPUT CHAIN I jack. In a similar manner
letter N on the diagonal board to the third set of "commons".

SETTING SWITCHES + (CHAIN, SEARCHING, CARRY, INPUT).

After the drums have been attached and the plugging finished, the

next step is to set the switches controlling the chain to be used, the
letter at which searching is to be done, and the type of input, single or
double. These switches art located in a panel 26 1/2 inches high and 8 1/2
inches wide on the right hard end of the bombe as seen from the front.
There are four columns of toggle switches. At the top of the first column
is a switch labelled "CHAIN 1, OFF-ON". There are similar switches at the
top of each of the other columns for chains 2 and 3. In each column below
the chain switch are 26 searching switches labelled and reading downwards
from Z to A. At the bottom of the second column is the CARRY OFF-ON switch.
On the 30 point machine there is a DOUBLE INPUT, OFF - ON switch at the
bottom of the fourth column. At the bottom of the third column is the CARRY
HOME, OFF - ON switch. On the older 39 point bombe the setting of the
machine for the type of input is accomplished by the insertion of a single
or double input plugboard. The receptacle for this plugboard is located on
the left hand end of the machine as seen from the front.

In the description above of setting up the bombe for "Test Menu No.1"

the menu was only set up on 7 enigmas connected to the input of CHAIN 1.
Hence CHAIN 1 switch is operated to the ON position and all other CHAIN
switches to the OFF position. It is specified in "TEST MENU NO.1" that the
current entry shall be at "A". The "A" searching switch in the first column
is therefore operated and all the other searching switches in all the
columns are restored to the OFF position. This menu is of the single input
type, so the DOUBLE INPUT switch remains in the OFF position. If the
bombe happens to be the old 39 point type, the SINGLE INPUT plugboard is
inserted in the machine. The CARRY and CARRY HOME switches must be OFF.
Operate the MOTOR and CONTROL switches. (The MOTOR switch is at the left
and the CONTROL switch is at the right as you face the bombe). Depress the
START key. (The START key is at the right as you face the bombe). Operate
the CARRY switch when the bombe has attained its normal running speed.

BOMBE RUNNING AND SENSING - ELECTRICAL CONTROL CIRCUIT.

The bombe as it is running is essentially a mechanical mechanism

operating under the control of an electrical relay circuit. This relay
circuit consists of 34 control relays, 2 high speed relays and 4 sets of 26
sensing relays each for the detection of the straight or OC which indicates
a possible solution, 26 stop relays for controlling the stopping of the
bombe at a proper place to indicate the straight, 2 clutch magnets for
controlling the driving mechanism, 2 sets of dual carry magnets for each of
the three banks, 7 multi relays for closing the circuits to the indicating
unit coils sets of 26 indicating unit coils, a heavy duty coil for opening
the sensing circuit when The operator is verifying the indicated stop, 6
circuit breakers for making and breaking the sensing circuit with
sufficient margin to prevent it being made or broken on the commentators
associated with the drums, and 11 cams and contacts for controlling the
time of making and breaking of the control circuits. The circuit is shown
in a block diagram on page 70.

A round core relay with the spring pile-up mounted above the core is

used for the control relays and stop relays. The armature is hinged at the
front of the relay and acts as a lever to push the moving spring upward
away from the coil. The relay is of moderately heavy construction. It is
designed to operate in .007 - .008 seconds and is known as the standard
general purpose International Business Machines Corp. or British Tabulating
Machine Co. Ltd. relay.

The two high speed relays are of the telegraph sounder type with two

round spool magnets mounted vertically with respect to the base. The spring
pile-up is also mounted vertically and is


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