The legend of the Philadelphia Experiment claims the USS Eldridge was rendered invisible (and possibly teleported) in 1943 using electromagnetic equipment. The truth is rooted in the very real practice of degaussing—wrapping ships' hulls in electrical cables to neutralize their magnetic signature and protect against magnetic mines.
Degaussing was genuinely secret and genuinely strange-looking: ships wrapped in massive coils undergoing calibration did appear to shimmer or create unusual visual effects, particularly in certain lighting conditions. The process was classified, and sailors were forbidden from discussing it.
The conspiracy theory originated with Carl M. Allen (Carlos Allende), who wrote annotated letters to astronomer Morris K. Jessup in 1955, claiming to have witnessed the experiment. While the story has been thoroughly debunked—Navy records show the Eldridge was nowhere near Philadelphia in October 1943—it illustrates how wartime secrecy and genuine technological marvels combined to create enduring myths.