186 | 18 DElIlAH—ENCRyPTING SPEECH
As with Tunny, the receiver’s Delilah had to be synchronized with the sender’s, so that both
the transmitting and receiving machine produced identical key. In designing Delilah, Turing
ingeniously adapted existing cryptographic technology. At the heart of Delilah’s mechanism for
producing the key was a five-wheeled text-enciphering machine modelled on Enigma.
The receiving machine stripped the key from the enciphered message and the resulting
decrypted numbers (specifying voltages) were used to reproduce the original speech. The result
was a bit crackly, but was generally quite intelligible—although if the machine made a mistake,
there would be ‘a sudden crack like a rifle shot’, Turing said.^21 It must have been hard on the
receiving operator’s straining ears. But Turing had succeeded: Delilah was a functioning port-
able speech-encryption system that was only a fraction of the size of the gigantic SIGSALY.
mess life
At Hanslope, Turing lived in an old cottage and took his meals in the army mess.^22 As the com-
manding officer recollected:^23
In spite of having to live in a mess and with soldiers, Turing soon settled down and became
‘one of us’ in every sense; always rather quiet but ever ready to discuss his work even with an
ignoramus like myself.
figure 18.1 Turing’s Delilah.
From A. M. Turing and D. Bayley, ‘Speech secrecy system “Delilah”, Technical description’, c. March 1945, National Archives ref. HW
25/36. Crown copyright and reproduced with permission of the National Archives Image Library, Kew.