The US 6812 Division Bombe Report Eastcote 1944 Page 74

Tony Sale's Codes and Ciphers

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CHAPTER III. - DESCRIPTION AND CHARACTERISTICS OF BOMBE AND CHECKING
MACHINE.

GENERAL DESCRIPTION.

The Bombe ( figs. 44 and 45) made by the British Tabulating Machine

Company Ltd. is a portable electro-mechanical device for the rapid decoding
of enigma machine messages. It contains the equivalent of the wheels and
"uncle walters" of 36 enigma machines and is motor driven. There are four
current inputs and three stecker boards. The bombe operates on 220 volts
direct current which in the case of U S A bay is obtained from a mercury
arc rectifier connected to the 220 volt alternating current mains. It is a
self contained unit only requiring connection to a power line.

WEIGHT.

The bombe weighs approximately one ton.


POWER CONSUMPTION.

The total consumption of the bombe is about 10 amperes. Its supply

leads are fused on both sides of the line with 12 ampere fuses. The motor
is a Thomson Houston Shunt Wound Direct Current 220 Volt Motor rated at
0.75 horsepower and drawing 3.8 amperes when running at 800 rpm or 3.42
amperes at 1000 rpm.

OPERATING SPEED.

The bombe is designed to operate at a speed of 64 carries per minute

(64 steps of the drums of the middle row per minute). Each step of the
middle row follows a complete revolution of the fast drums (top row)
providing the "carry" circuit is operative.

INSTALLATION AND PREPARATION FOR USE.

The following procedure is necessary to install the bombe and make it

ready for use. The machine is put in position and the current supply leads
connected to the power mains. The Motor and Control power switches should
be in the OFF position when this is done. The bombe is inspected for
general condition to detect any breakage or damage that may have occurred
during shipment. The machine shall be completely lubricated. All
adjustments of the drive and carry mechanisms and of the relays are
inspected. The "hot spot" on the control cam is blocked out so that the
bombe will not latch up at setting ZZZ and then the machine is run for 24
hours to wear in all the moving parts.

RELOCATION OF MOTOR AND CONTROL SWITCHES.

When the bombe is received from the factory the Motor and Control

power switches are located at the bottom on the right hand end of the
machine. These are relocated to a position adjacent to the Start and Stop
switches as shown on figure 44.

RUNNING TEST MENUS.

In order to prove the proper functioning of the bombe it is necessary

to set up test menus and run them to get the expected right stops. These
test menus are shown in figures 46 to 50 inclusive. The first step in
setting up the machine for these menus is to attach the wheels in the
proper wheel order as indicated at the top of the menu.

ATTACHING DRUMS.

The drums to be used are specified in the wheel order assignment. For

instance in figure 46, test menu no.1 calls for wheels 3 2 4. This means
that no.3 drums shall be used for the top or fast drums, no.2 shall be used
for the intermediate, and no.4 shall be used for the bottom or slow drum.
By referring to the table of drum color codes on page 9, it will be found
that the no.3 drums are green, no. 2 maroon and no. 4 are yellow.


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