I remember learning about how Patton had staged a fake army in Great Britain to trick the Germans a little before Operation Neptune. And that the Germans expected the Allies to land at Calais being led by Patton. But why would they need to fake an army? What good does that do? Why does it matter if the Germans saw the real or fake army?
There wasn’t a fake army in that an army existed simply for the sake of tricking the Germans, but rather one that existed on paper and in radio traffic but not physically if that makes sense. The First US Army Group (FUSAG) was created with the express purpose of deceiving the German military into believing that the Allied invasion of mainland Europe would occur at Calais. It was also widely believed that Patton, arguably one of the Allies most aggressive commanders, would be taking part in the invasion, his aggressive character being a desirable trait when the aim is to rapidly advance inland.
Placing Patton in charge of FUSAG lent credibility to the already strong belief that the Allies would attack Calais. Except their was no FUSAG, it existed only on paper. The only personnel assigned to it were radios operators who generated fake radio traffic intended for interception, engineers who constructed fake encampments and inflatable vehicles to deceive Luftwaffe reconnaissance planes and Patton himself.
This was all part of Operation Quicksilver, the deception plan for deceiving the Germans into thinking that Calais was the target. Quicksilver was in turn part of Operation Fortitude which itself was part of Operation Bodyguard, the overall plan for deception operations pertaining to the invasion of Europe. Key to the success of these plans (and especially Quicksilver) was Operation Double Cross, the use of German double agents who communicated misinformation to their handlers. Double Cross agents reported the existence of FUSAG and so good was this information that when the Normandy invasion occurred, the continued presence of FUSAG in England led many in the German High Command to believe that the Normandy invasion was a diversion and the Patton would still lead the real invasion at Calais. To preserve the integrity of the Double Cross agents, the agents reported that because the Normandy “diversion” had been so successful, FUSAG had been broken up and transferred south for embarkation and transportation to Normandy.