Cracking the Enigma

Fifteen thousand people kept the secret of Britain's most important intelligence advantages during the Second World War. The 15,000 were employed by the British Secret Intelligence Service, MI6, at Bletchly Park, a Bedfordshire country estate, monitoring and decoding Germany's most secret communications. At the heart of their achievement was the German enigma code machine and . . . a simple weather report. Each morning at dawn, a German double agent prepared - with the help of the British Security Service, MI5 - a routine weather report. The report was transmitted to German Abwehr chiefs in Hamburg, then coded on the Enigma machine and sent on to Berlin. The codes used on the Enigma were regarded by Germans to be unbreakable, and as a safeguard, the codes were altered each day. In fact, all the precautions were useless. By monitoring the coded signals to Berlin, and comparing it with the original weather report, the Bletchly code-breakers were able to work out the Enigma code for the day within a few hours of dawn. The rest of the day’s messages would then be deciphered almost as soon as they were transmitted.