The legend of the Philadelphia experiment states that the US Navy conducted in August 1943 a series of maritime experiments for achieving radar invisibility. These experiments took place off the coast of Philadelphia on a destroyer called the USS Eldridge and were allegedly attended by the best science minds of the time, including Albert Einstein, Nicola Tesla and John von Neumann.
This distinguished college, along with the Navy brass, got more than they bargained for. The ship did not only become invisible to radar, it also vanished from their eyes into a cloud of green haze, leaving only a ship-shaped depression in the water. At around the same time, the ship was seen off Newport Mews, where it had been built. After a second event of teleportation, the ship reappeared off Philadelphia but now most of the crew were terminally insane, if not physically embedded in the ship's steel bulkheads.
The legend is known through a witness known as Carlos Allende and has been somewhat documented and researched by Morris Jessup. The latter was later found dead of an obviously staged suicide. Ever since, there has been a cottage industry of research and rumors around the Philadelphia Experiment, later joined by the Montauk mythos.
The book 'Case for the UFO' by Morris Jessup is available for download from the Cassiopaea web site. Much of the original Philadelphia Experiment story is found there.
According to the QFS's understanding, an experiment involving some 'hyperdimensional' technology most likely took place with fairly disastrous results, more or less as in the original legend. It and its successors have been the subject of a disinformation effort ever since. So, while some of the Philadelphia story may be true, the matter has been deliberately confused since. The murder of Jessup may also have been made obvious in order to dramatize the story further, so as to draw the inquisitive crowd all on this trail while follow up work went elsewhere.
The Philadelphia Experiment (PX) story has been specially promoted by alleged witness and survivor Al Bielek, by many accounts a conman and likely disinformation agent.