The Ghost Army was a United States Army tactical deception unit during World War II officially known as the 23rd Headquarters Special Troops. The 1,100-man unit was given a unique mission within the Army to impersonate other U.S. Army units in order to fool the enemy. From a few weeks after D-Day, when they landed in France, until the end of the war, they put on a traveling road show, using inflatable tanks, sound trucks, phony radio transmissions and even playacting. They staged more than 20 battlefield deceptions, often operating very close to the front lines.

The Ghost Army (Wikipedia)