History's Mysteries - The True Story of the Philadelphia Experiment (History Channel Documentary)
Narrated by David Ackroyd
The Philadelphia Experiment is an alleged military experiment supposed to have been carried out by the U.S. Navy at the Philadelphia Naval Shipyard in Philadelphia, Pennsylvania, sometime around October 28, 1943. The U.S. Navy destroyer escort USS Eldridge (DE-173) was claimed to have been rendered invisible (or "cloaked") to enemy devices.
The story first appeared in 1955, in letters of unknown origin sent to a writer and astronomer, Morris K. Jessup. It is widely understood to be a hoax; the U.S. Navy maintains that no such experiment was ever conducted, that the details of the story contradict well-established facts about USS Eldridge, and that the alleged claims do not conform to known physical laws.
~ Summary from Wikipedia