CHAPTER 12

Bombes

jack copeland (with jean valentine

and catherine caughey)

T

uring’s Enigma-cracking ‘bombe’ was one of his major contributions to winning

the war. His revolutionary machine gave the Allies open access to Germany’s secret

military communications. This chapter explains what the bombe was for and how it

worked. Jean Valentine and Catherine Caughey, both Bletchley Park ‘Wrens’, describe their

first encounters with Turing’s awe-inspiring bombes. They speak of the morale-sapping

secrecy that surrounded the work of bombe operators. Jean Valentine also describes a visit to

the secret factory where the bombes were made.^1

from bomba to bombe

Poland’s codebreakers were reading German military Enigma from early 1933. Their intellectual

leader was the legendary Marian Rejewski, one of the twentieth century’s greatest codebreakers.

As explained in Chapter 11, Rejewski and his colleagues invited a party of their British oppo-

site numbers to Poland a few weeks before Hitler’s army poured across the frontier. An ultra-

secret meeting took place at the Biuro Szyfrów (the cipher bureau), a cluster of buildings hidden

in the forest at Pyry, near Warsaw. The visitors included Dilly Knox, at that time Britain’s most

experienced warrior against Enigma (see Chapter 11), and Commander Alastair Denniston,

head of British military and civil codebreaking.

‘The Poles called for us at 7 a.m.’, recalled Denniston, ‘and we were driven out to a clearing in

a forest about 20 kilometres from Warsaw’.^2 The Poles had decided to reveal everything before

it was too late. ‘At that meeting we told everything we knew and showed everything we had’,

Rejewski said.^3 After the meeting, Knox sang for joy—although his immediate reaction, as he

had sat listening to Rejewski’s codebreaking triumphs, had been undisguised fury that the Poles

were so far ahead of him.^4

In 1938 Rejewski and his colleagues had built a small machine they called a ‘bomba’.^5 Their

reasons for choosing this distinctive name, whose literal meaning is ‘bomb’ or ‘bombshell’, went

unrecorded at the time, and theories later abounded. At Bletchley Park Turing told Joan Clarke,

to whom he was briefly engaged, that the bomba ‘got this nickname because it made a ticking