On June 27, 1940, the Germans set up two-way radio communication in their newly occupied French territory, employing their most sophisticated coding machine, Enigma, to transmit information.
The Germans established radio stations in Brest and the port town of Cherbourg.
Signals would be transmitted to German bombers so as to direct them to targets in Britain.
The Enigma coding machine, invented in 1919 by Hugo Koch, a Dutchman, looked like a typewriter and was originally employed for business purposes.
The German army adapted the machine for wartime use and considered its encoding system unbreakable. They were wrong.
The Brits had broken the code as early as the German invasion of Poland and had intercepted virtually every message sent through the system. Britain nicknamed the intercepted messages Ultra.