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noise, like an anarchist’s time bomb’ (as she recollected).^6 On the other hand, Jean Valentine
(Fig. 12.12) remembers the bombes’ operators being told that the name had arisen because, at
a certain point in the bomba’s operations, it would release a metal component that fell to the
ground ‘like a bomb’. American military personnel stationed at Bletchley Park and its outsta-
tions were told the same story, reporting back to Washington that the Polish machine was so
named because ‘When a possible solution was reached a part would fall off the machine onto
the floor with a loud noise’.^7
It is certainly possible that a falling weight disengaged the bomba’s drive mechanism—an
early computer printer designed by the Victorian computer pioneer Charles Babbage, part of
his Difference Engine, involved the same idea. However, a sketch of the bomba by Rejewski
shows no mechanism involving falling weights, and perhaps indicates that the bomba’s stop-
ping mechanism was magnetic in nature.^8 Another explanation of the name is that Rejewski was
eating a bomba—a type of ice-cream dessert, bombe in French—when the idea for the machine
struck him.^9 Military historian Michael Foot reported being told by Rejewski himself that the
name had originated in this way.^10
Rejewski’s bomba consisted of six replicas of the Enigma. His machine worked well, and the
prototype bomba spawned several bomby (the plural of ‘bomba’). By November 1938 the Biuro
Szyfrów had half-a-dozen bomby slogging away at the German Enigma traffic.^11 Denniston and
Knox saw the bomby first-hand: ‘we were taken down to an underground room full of electric
equipment and introduced to the “bombs” ’, Denniston remembered.^12
The bomba depended on a weakness, unnoticed by the Germans, in their Enigma operating
procedures. There was a flaw in the method that the sending operator used to tell the receiving
figure 12.1 A bombe at the Eastcote outstation: notice the swastikas that someone has doodled along the top of
the bombe cabinet and the Keep Feet Off sign at the bottom right.
The Turing Archive for the History of Computing.