Shortly after the D-Day invasion on June 6, 1944, two Frenchmen on bicycles managed to cross the perimeter of the United States Army’s 23rd Headquarters Special Troops and what they saw astounded them. Four American soldiers had picked up a 40-ton Sherman tank and were turning it in place. Soldier Arthur Shilstone says, “They looked at me, and they were looking for answers, and I finally said: ‘The Americans are very strong.’”
===============The passage above is the opening paragraph of an interesting article at Smithsonian.com, discussing the recently broadcast documentary, The Ghost Army. You can read the article here: When an Army of Artists Fooled Hitler.
The show aired on May 21, and DVDs are for sale, but it doesn't appear to be available for streaming yet. Here's the documentary website.
Of course the first thing I thought of upon reading this were the so-called "Quaker Guns" of the Civil War era, though the WWII subterfuge is exponentially more elaborate. Civil War Quaker Guns were logs painted black to resemble artillery pieces, intended to fool the enemy into thinking fortifications were still occupied. Most famous, perhaps, was Joe Johnston's use of Quaker Guns at Centreville in March, 1862, to help mask his army's movement toward the Rappahannock River. The use of Quaker Guns in this country predates the Civil War, however. Lieutenant Colonel William Washington, George Washington's 2nd cousin once removed, used the trick to good effect against Loyalists in South Carolina in 1780.
[Below: Quaker Gun, Centreville, Virginia. Library of Congress Civil War glass negative collection.]