From September 1940, Bletchley Park’s decryption of the German Luftwaffe (Air Force) ‘Brown’ Enigma key played a crucial part in protecting the UK during the Battle of Britain and the Blitz.
Brown was used by the German Air Force’s radio and research regiment. In 1940, they were responsible for two beam navigation systems used by the Luftwaffe to direct their night bombing raids over Britain. Brown messages gave valuable information about the systems, allowing the British to jam navigational beams and divert German bombers away from their targets. They also helped identify the target for each night’s raid – if Hut 6 was able to decrypt the messages in time.
But the Brown network contained more information than could be read in the messages themselves. Traffic analysis at Y (wireless intercept) stations listening to Brown traffic built up a detailed picture of German navigation beam operations, from transmitter locations to operational information.