In the autumn of 1943, according to some accounts, the US Navy succeeded in making a ship invisible, both to the naked eye and to radar systems. The USS Eldridge, so the story goes, was part of an experiment dubbed Project Rainbow — now more commonly known as the Philadelphia Experiment — which sought to test invisibility technology that used electromagnetic fields to bend space and time. Some “witnesses” have claimed that they saw the vessel disappear from view for several minutes, and it has even been suggested that during this time the Eldridge was “teleported” from the US port of Philadelphia in Pennsylvania, to Norfolk in Virginia, some hundreds of miles down the coast.

This story is now widely believed to be a hoax, with official Navy records placing the USS Eldridge nowhere near Philadelphia during that part of 1943. It is certainly true, however, that “invisibility” has been a key factor in how we conduct warfare since ancient times. As the Chinese general Sun Tzu wrote in The Art of War — which, dating from around 450 BC, is probably the world’s oldest treatise on military strategy — “all warfare is based on deception”. The military quest for invisibility also appears in Greek mythology: Perseus’ helmet and Gyge’s ring rendered their wearers invisible, which proved useful for fighting monsters and formed the basis for the “One Ring” in Tolkien’s famous books.

Such abilities no longer remain in the realm of fantasy, however. In the March issue of Physics World, Chris Lavers reviews some of the techniques modern warships are employing to disguise themselves from attackers.

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