80 | 9 AT BlETCHlEy PARk
84,000 Enigma messages each month—two messages every minute.^5 Chapter 12 describes the
bombes and explains how they worked.
The U-boat peril
Turing also undertook, single-handedly at first, a 20-month struggle to crack the especially
secure form of Enigma used by the North Atlantic U-boats. With his group he first broke into
the current messages transmitted between the submarines and their bases during June 1941,
the very month when Winston Churchill’s advisors were warning him that the wholesale
sinkings in the North Atlantic would soon tip Britain into defeat by starvation.^6 Churchill,
Britain’s bulldog-like wartime leader, later confessed: ‘The only thing that ever really fright-
ened me during the war was the U-boat peril’.^7 Turing’s work had at last made it possible
to defuse that peril. The U-boats’ messages revealed their positions, and so the merchant
convoys could simply be rerouted away from the submarines—a simple but utterly effective
measure.
Breaking Tunny
Turing also searched for a way to break into the torrent of messages suddenly flooding from a
new, and much more sophisticated, German cipher machine (described in Chapter 14). British
intelligence code-named the new machine ‘Tunny’.
figure 9.1 The Mansion, Bletchley Park.
Reproduced with permission of the Bletchley Park Trust.