From Wikipedia:
The Philadelphia Experiment is the name of an alleged naval military experiment said to have been carried out at the Philadelphia Naval Shipyard in Philadelphia, Pennsylvania, USA sometime around October 28, 1943. It is alleged that the U.S. Navy destroyer escort USS Eldridge was to be rendered invisible (or “cloaked”) to enemy devices. The experiment is also referred to as Project Rainbow.
The story is widely regarded as a hoax.[1][2][3]
Those first 3 references debunk the story. Of course people will believe what they want…