Officially known as Project Rainbow, the experiment was to be a military application of a Unified Field Theory, a term coined by Einstein. The Unified Field Theory postulates that it may be possible, with specialised equipment and sufficient energy, to bend light around an object in such a way as to render it essentially invisible to observers. The US Navy, currently engaged in World War II, considered this application of the theory to be of obvious military value and approved and sponsored the experiment. A destroyer escort, USS Eldridge, was allegedly fitted with the required equipment at the naval yards in Philadelphia.
It is also alleged that the equipment was not properly calibrated, which may have caused the results of the experiment. When the equipment was turned on during the experiment, the USS Eldridge is alleged to have not only become almost entirely invisible to the naked eye but actually vanished from the area in a flash of blue light.
Elsewhere, the U.S. naval base at Norfolk, Virginia, just over 215 miles away, is alleged to have reported sighting the Eldridge offshore, whereupon the Eldridge vanished from their sight and reappeared in Philadelphia at the site it had originally occupied, in an apparent case of accidental teleportation.
The physiological effects of the experiment on the crew of the Eldridge were profound - all of the crew were violently ill. Some were alleged to have suffered from mental illness as a result of their experience; behaviour consistent with schizophrenia is described in other accounts. Other members, like Jacob D. Murray, were physically unaccounted for - supposedly "vanished" - and five of the crew were allegedly fused to the metal bulkhead or deck of the ship. Still, others were said to fade in and out of sight. Sometimes they would disappear, and burst into flames.
Horrified by these results, Navy officials immediately cancelled the experiment. All of the surviving crew involved were discharged; in some accounts, brainwashing techniques were employed in an attempt to make the remaining crew members lose their memories concerning the details of their experience.
Morris Jessup and Carlos Miguel Allende
In 1955, Morris K. Jessup, an amateur astronomer and former graduate-level researcher, published The Case for the UFO, a book about unidentified flying objects which contained some theorising about the means of propulsion that flying-saucer-style UFOs might use.
On January 13, 1955, Jessup received a letter from a man who identified himself as Carlos Allende. In the letter, Allende informed Jessup of the Philadelphia Experiment, alluding to two poorly sourced contemporary newspaper articles as proof. Allende also said that he had witnessed the Eldridge disappear and reappear while serving aboard the SS Andrew Furuseth, a nearby merchant ship. He also named other crew members with whom he served and claimed to know the fate of some of the crewmembers of the Eldridge after the experiment.
When Jessup responded asking for more details, the correspondent identified himself as Carl M. Allen. Allen said that he could not provide the details for which Jessup was asking, but implied that he might be able to recall by means of hypnosis. Suspecting that Allende/Allen was a fraud, Jessup decided to discontinue the correspondence.
The Office of Naval Research and the Varo annotation
Jessup was contacted by the Office of Naval Research (ONR) during the spring of 1957 and asked to study a paperback copy of his UFO book that had been mailed to ONR in a manila envelope marked "Happy Easter". On examination, the book had been extensively annotated by hand in its margins, and an ONR officer asked Jessup if he had any idea as to who had done so.
The annotations were written in three different colours of ink, and appeared to detail a correspondence among three individuals, only one of which is given a name: "Jemi". The ONR labelled the other two "Mr A" and "Mr B". Based on the handwriting style and subject matter, Jessup identified "Mr A" as Allende/Allen.
Later, the ONR contacted Jessup, claiming that the return address on Allende's letter to Jessup was an abandoned farmhouse. They also informed Jessup that the Varo Corporation, a research firm, was preparing a print copy of the annotated version of The Case for the UFO, complete with both letters he had received. About a hundred copies of the Varo Edition were printed and distributed within the Navy. Jessup was also sent three for his own use.
Jessup attempted to make a living writing on the topic, but his follow-up book did not sell well and his publisher rejected several other manuscripts. In 1958 his wife left him, and friends described him as being depressed and somewhat unstable when he travelled to New York. After returning to Florida he was involved in a serious car accident and was slow to recover, apparently increasing his despondency. Morris Jessup committed suicide in 1959. Many conspiracy theorists believe that the government murdered him because of his knowledge of the Philadelphia Experiment.
In 1984, the story was eventually adapted into a motion picture, The Philadelphia Experiment directed by Stewart Rafill. Though based only loosely on prior accounts of the experiment, it served to bring the core elements of the original story into mainstream scrutiny.
Researcher Jacques Vallee describes a procedure on board USS Engstrom (DE-50), which was docked alongside Eldridge in 1943. The operation involved the generation of a powerful electromagnetic field on board the ship in order to degauss it, with the goal of rendering the ship undetectable - "invisible" - to magnetically triggered torpedoes and mines. A Canadian invented this system, and the British used it widely during the Second World War. British ships of the era often included such systems built-in on the upper decks (the conduits are still visible on the deck of the HMS Belfast (C35) in London). Degaussing is still used today; however, it has no effect on visible light or radar. Vallee speculates that accounts of the Engstrom's degaussing may have been garbled in subsequent retellings, and these accounts may have influenced the story of the Philadelphia Experiment.