The truth of this story should be considered to be highly speculative.
The experiment was allegedly conducted by one Dr. Franklin Reno (or Rinehart) as a military application of Albert Einstein's Unified Field Theory, or "Generalized Theory of Gravitation". The theory, briefly, postulates the interrelatedness of the forces which comprise electromagnetic radiation and gravity. Through a special application of the theory, it was thought to be possible, with specialized equipment and enough energy, to bend light around an object, rendering it essentially invisible. The Navy considered this application to be of obvious value in wartime (as the United States was engaged in World War II at the time) and approved and sponsored the experiment. A Navy destroyer, the USS Eldridge, was fitted with the required generator equipment at the Naval Yards in Philadelphia.
Testing began in the summer of 1943, and was initially successful to a limited degree. One test, on July 22, 1943, resulted in the Eldridge being rendered almost completely invisible, with some eyewitnesses reporting a "greenish fog" - however, crew members complained of serious nausea afterwards. At that point, the experiment was altered by the request of the Navy, with the new goal being invisibility to radar only.
Equipment was recalibrated, and the experiment was performed again on October 28. This time, the Eldridge not only actually became almost entirely invisible to the naked eye, but actually vanished from the area entirely in a flash of blue light. Concurrent with this phenomenon, the U.S. Naval base at Norfolk, Virginia, just over 600 km away, reported sighting the Eldridge offshore for several minutes, at the end of which time the Eldridge vanished again and reappeared in Philadelphia, at the site it had originally occupied - a accidental case of supposed teleportation.
The physiological effects on the crew were profound. Almost all of the crew were violently ill. Some suffered from mental illness because of the experience - behavior conforming to schizophrenia is described in some accounts. Still other members were missing - supposedly "vanished" - and allegedly five of the crew were actually fused to the metal bulkhead or deck of the ship. Horrified, Navy officials immediately cancelled the experiment. All of the surviving crew involved were discharged; in some cases, brainwashing was used to make crew members forget about the details of their experience.
The details of this supposed experiment were revealed to the public in a roundabout way.
In 1955, Morris K. Jessup, an amateur astronomer and former graduate-level researcher, published The Case for the UFO, an examination of the phenomenon of UFO's which contained some theorization as to the means of propulsion that flying saucer-style UFO's may use. Jessup speculated that anti-gravity and/or electromagnetism may have been responsible for the observed flight behavior of UFO's, and lamented, both in the book and the publicity tour which followed, that space flight research was concentrated in the area of rocketry, and that little attention was paid to these other theoretical means of flight, which he felt would ultimately be more fruitful in the long run.
On January 13, 1956, Jessup received a letter from a man identifying himself as "Carlos Miguel Allende. In the letter, Allende informed Jessup of the Philadelphia Experiment, alluding to poorly sourced contemporary newspaper articles as "proof". Allende also said that he had personally witnessed the Eldridge disappear and reappear while serving aboard a merchant marine ship in its vicinity, the SS Andrew Furuseth. He further named other crew with which he served aboard the Andrew Furuseth, and claimed to know of the fates of some of the crew members of the Eldridge after the experiment, including one whom he witnessed "disappear" during a choatic fight in a bar. Jessup replied to Allende by postcard, asking for further evidence and corroboration for the story, such as dates and specific details of his fantastic story. The reply came months later; however, this time the correspondant identified himself as "Carl M. Allen". Allen said that he could not provide the details for which Jessup was asking, but implied that he may be able to recall by means of hypnosis. Jessup decided to discontinue the correspondence.
In the spring of 1957, Jessup was contacted by the Office of Naval Research in Washington, D.C and requested to study the contents of a parcel that they had received. Upon arrival, a curious Jessup was astonished to find that a paperback copy of his book had been mailed to ONR in a manila envelope marked "HAPPY EASTER". Further, 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 lengthy annotations were written in three different colors of ink, and appeared to detail a correspondence between three individuals, only one of which is given a name: "Jemi". The ONR labeled the other two "Mr. A" and "Mr. B". The annotators refer to each other as Gypsies, and discuss two different types of "people" living in space. Their text contained nonstandard use of capitalization and punctuation, and detailed a lengthy discussion of the merits of various suppositions that Jessup makes throughout his book, with oblique references to the Philadelphia Experiment, in a way that suggested prior or superior knowledge. (For example, "Mr. B" reassures his fellow annotators, who have highlighted a certain theory of Jessup's, "HE HAS NO KNOWLEDGE, HE COULD NOT HAVE. ONLY GUESSING." [sic])
Based on the handwriting style and subject matter, and in comparison to the earlier letters he had received, Jessup identified "Mr. A" as Carlos Allende/Carl 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.
Morris Jessup committed suicide, apparently for reasons unrelated to his book, in 1959.
In 1965, Vincent Gaddis published Invisible Horizons: True Mysteries of the Sea, in which the story of the experiment from the Varo annotation is recounted.
Later, in 1977, Charles Berlitz, an author of several books on paranormal phenomena, included a chapter on the experiment in his book Without a Trace: New Information from the Triangle (though it should be noted that the experiment did not take place within the so-called Bermuda Triangle).
In 1978, a novel, Thin Air, was released. This was a dramatic fictional account, clearly inspired by the foregoing works, of a conspiracy to cover-up an horrendous experiment gone wrong on board the USS Eldridge in 1943. However, a year later, Berlitz and a co-author, William L. Moore, published The Philadelphia Experiment: Project Invisibility which, though it claims to be fact, as Berlitz's previous books do, plagiarizes Thin Air.
Two dramatic movies have been released on the subject: The Philadelphia Experiment (1984) and Philadelphia Experiment II (1993). They are best described as science fiction.
The Experiment has been the subject of several television shows dealing with the paranormal and conspiracy theories, including The Unexplained, a series produced by Bill Kurtis on the cable television network The Arts and Entertainment Network (A&E).
Detractors, skeptics, and other researchers have noted several serious issues and problems with the story of the Philadelphia Experiment.
Researcher Jacques Vallee describes a supposedly documented experiment on board the USS Engstrom, which was docked alongside the Eldridge in 1943. The operation involved the generation of an electromagnetic field on board the ship in order to degauss it, with the goal of rendering the ship undetectable - "invisible" - to magnetically guided torpedoes. He speculates that this may have resulted in mistaken tales of making ships invisible by inattentive sailors.
A veteran who served on board the Engstrom noted that the Eldridge could indeed have gotten from Philadelphia to Norfolk and back again in a single day at a time when merchant ships could not have - by use of the Chesapeake and Delaware Canal, which at the time was open only to Naval vessels.
It should be noted that this same veteran claims to be the man whom Allende witnessed "disappear" at a bar. He claims that when the fight broke out, friendly barmaids whisked him out the back door of the bar before the police arrived, because he was underaged. They then "covered" for him by claiming that he "disappeared".
In a more speculative and strongly paranormal vein, Al Bielek and Duncan Cameron both claim to have leaped from the deck of the Eldridge while it was in "hyperspace" between Philadelphia and Norfolk, and ended up, after a period of severe disorientation, at Montauk Point, Long Island in the year 1983, having experienced not only teleportation but time travel. This episode is a seminal event in another alleged secret and horrific U.S. Government experiment into the paranormal known as the Montauk Project.
Links:
The Story of the Experiment
Publication of the Story
Morris Jessup and Carlos Miguel Allende
The ONR and the Varo Annotation
Later Publications of the Story
Problems with the Story
Alternate Explanations and Stories