The Philadelphia Experiment was an alleged event claimed to have been witnessed by an ex-merchant mariner named Carl M. Allen at the United States Navy's Philadelphia Naval Shipyard in Philadelphia, Pennsylvania, United States, some time around October 28, 1943. Allen described an experiment where the U.S. Navy attempted to make a destroyer escort, USS Eldridge, disappear and the bizarre results that followed.
The story surfaced in late 1955 when Allen sent a book full of hand-written annotations referring to the experiment to a U.S. Navy research organization and, a little later, a series of letters making further claims to a UFO author. Allen's account of the event is widely understood to be a hoax.