Code-breaking on Bombe machines, c 1943.

UNITED KINGDOM - OCTOBER 23: This is a Bombe unit room at Eastcote in Middlesex. The Bombe machine was used extensively during WWII to crack top secret German military communiques. This is said to be similar to the Bombe unit room in Hut 11 at Bletchley Park in Buckinghamshire, the British forces' intelligence centre during WWII. Several such Bombe units were sited throughout North Buckinghamshire, and by 1944 there were over 200 machines in operation. The Bombe machine was a less sophisticated codebreaker than 'Colossus' at Bletchley Park, the world's first electronic programmable computer. (Photo by SSPL/Getty Images)