98 | 11 BREAkING mACHINES wITH A PENCIl
for ‘professor types’ during both world wars—including Dillwyn (Dilly) Knox (Fig. 11.1) in the
first and Alan Turing in the second.
Until the time of Turing’s arrival, mostly classicists and linguists were recruited. Knox him-
self had an international reputation for unravelling charred fragments of Greek papyri. Shortly
after Enigma first came on the market in 1925, offering security to banks and businesses for
their telegrams and cables, the GC&CS obtained two of the new machines, and some time
later Knox studied one of these closely. By the beginning of 1939 he was still the only person at
the GC&CS to have worked successfully on Enigma messages. A rewired version of the com-
mercial Enigma machine, lacking the plugboard, had been used for military purposes during
the Spanish Civil War (1936–39) and Knox broke the machine’s wirings, using methods he
devised while experimenting with the (differently wired) commercial machine held by the
GC&CS.
When Turing was sent to join him in the pre-war months,^1 Knox was probably working
on one of the several German Enigma ‘cribs’ that the French or Polish cipher bureau had
given to the GC&CS.^2 ‘Crib’ was the term used for a stretch of plaintext corresponding to
part of a coded message: cribs would later play a huge part in Bletchley Park’s successes
against Enigma (see Chapter 12). But not even Turing and Knox could unravel the system
from these early cribs. They would not make much headway until August 1939, after Knox
met with the Polish codebreakers at their headquarters near Warsaw. The Poles had been
breaking German military Enigma messages since the early 1930s, and they decided to hand
over their secrets just before their country was invaded. Knox seized on the Poles’ infor-
mation and, shortly before Turing joined the Enigma attack full time in September 1939,
Knox’s assistant Peter Twinn used a monster crib—supplied, ironically, by the Germans
figure 11.1 Dilly Knox, sketched by
Gilbert Spencer.
Reproduced with permission of Mavis Batey.