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delay before we could begin our important work. Perhaps the security people were investigating
our backgrounds. Anyway, after about 10 days we were suddenly taken back to Block B and were
shown how to operate a bombe.
meet the bombe
Housed in a large metal cabinet and weighing about a ton, the bombe was over 7 feet long,
nearly 3 feet wide, and stood 6 feet 6 inches tall (see Fig. 12.1).^46 Turing’s colleague Patrick
Mahon, who later became head of Hut 8, described the bombe with a tinge of awe:^47
The bombe was a highly complicated electrical apparatus, involving some 10 miles of wire and
about 1 million soldered connections. Its intricate and delicate apparatus had to be kept in per-
fect condition or the right answer was likely to be missed . . . From one side, a bombe appears to
consist of 9 rows of revolving drums; from the other, of coils of coloured wire, reminiscent of a
Fairisle sweater.
Victory, the prototype bombe, contained thirty replicas of the Enigma machine; later mod-
els contained thirty-six replica Enigmas. The codebreakers could connect these replica Enigmas
together in whatever configuration was best for attacking a given message. Each of the ‘drums’
(visible in Fig. 12.1) mimicked a single Enigma wheel, and each trio of drums replicated a single
Enigma machine. The three special drums on the right, in the middle section, were called the ‘indi-
cator drums’: these displayed output. Victory’s first prey consisted of naval messages transmitted
on 26 and 27 April 1940. This first successful break was hard won: after a ‘series of misadventures
and a fortnight’s work the machine triumphantly produced the answer’, Alexander said.^48
As explained in Chapter 10, before the codebreakers could decrypt a message they needed
to know
• how the Enigma machine’s plugboard was connected up
• which three wheels were inside the Enigma that day
• what position the wheels were in when the operator had started to encipher the mess
age (see Fig. 12.4).The bombe searched at high speed, its drums spinning, and then it would suddenly come to
a stop, with three letters showing on the indicator drums—BOV, for example. These were the
machine’s guess at the position of the wheels at the start of the message.^49 A panel on the right-
hand side of the bombe (Fig. 12.3) recorded the machine’s guesses at plugboard connections—
not necess arily all the connections, but (with luck) enough of them to enable the codebreakers
to decrypt the particular message under attack. Later bombes, called ‘Jumbos’, were able to print
their output on paper by means of an electric typewriter.^50
Once the bombe stopped, its guesses were processed by a human codebreaker and tested
on a replica Enigma machine. If the message decoded, all was well—and if it didn’t, the bombe
operator restarted the bombe and the search continued.
As soon as the ‘bombe runs’ for one message were finished, the Wrens would reconfigure the
machine ready for the next message. Working at the rear of the machine, they replugged the
bombe’s complex inter-drum connections, in accordance with a ‘menu’ drawn up by the code-
breaker in charge (Fig 12.6).^51 ‘The back of the machine almost defies description,’ said bombe
operator Diana Payne, ‘a mass of dangling plugs on rows of letters and numbers’ (Fig. 12.7).^52