Sun Tzu tells us that all warfare is based on deception. During WWII, the 23rd Headquarters Special Troops were a unit of artists, set designers, and regular guys who used inflatable tanks, vehicles, and artillery; recordings played over loudspeakers; and other means to simulate US units and deceive the German army during operations from Normandy to the Rhine. While it was serious business, they seem to have had some fun doing it, too.
The Ghost Army is an hour-long documentary that tells their story. It uses film footage, interviews with some of the veterans of the unit, and a number of sketches and paintings done by the artists during their service. It's pretty good, if you're into WWII documentaries.