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, sometime around October 28, 1943. Allen described an experiment where the U.S. Navy attempted to make a destroyer escort, the USS Eldridge, disappear and the bizarre results that followed.

USS Eldridge (DE-173), a Cannon-class destroyer escort, was a ship of the United States Navy named for Lieutenant Commander John Eldridge Jr., who led an operation for the invasion of the Solomon Islands.