Operation Fortitude was the umbrella deception plan supporting the Normandy invasion. Its southern component, Fortitude South, created the fictional First United States Army Group (FUSAG) supposedly based in southeast England and aimed at Pas-de-Calais. General George Patton, whom the Germans respected and feared, was placed in nominal command to make it convincing.
The deception used every trick available: fake encampments with inflatable equipment, scripted radio traffic, double agents feeding disinformation, misleading press references, and even fake oil storage depots designed by the architect of the London Palladium. The German intelligence network in Britain had been entirely turned or neutralized through the Double Cross system, meaning every "spy" report reaching Berlin was actually Allied disinformation.
The plan was so successful that even after the Normandy landings on June 6, 1944, Hitler held back the 15th Army and Panzer reserves at Calais for weeks, convinced that Normandy was merely a diversion. This failure to counterattack decisively in the first critical days helped ensure the invasion's success.