<P> Before World War I, Tesla sought overseas investors . After the war started, Tesla lost the funding he was receiving from his patents in European countries . </P> <P> In the August 1917 edition of the magazine Electrical Experimenter, Tesla postulated that electricity could be used to locate submarines via using the reflection of an "electric ray" of "tremendous frequency," with the signal being viewed on a fluorescent screen (a system that has been noted to have a superficial resemblance to modern radar). Tesla was incorrect in his assumption that high frequency radio waves would penetrate water . Émile Girardeau, who helped develop France's first radar system in the 1930s, noted in 1953 that Tesla's general speculation that a very strong high - frequency signal would be needed was correct . Girardeau said, "(Tesla) was prophesying or dreaming, since he had at his disposal no means of carrying them out, but one must add that if he was dreaming, at least he was dreaming correctly ." </P> <P> In 1928, Tesla received U.S. Patent 1,655,114, for a biplane capable of taking off vertically (VTOL aircraft) and then of being "gradually tilted through manipulation of the elevator devices" in flight until it was flying like a conventional plane . Tesla thought the plane would sell for less than $1,000, although the aircraft has been described as impractical . This would be his last patent and at this time Tesla closed his last office at 350 Madison Ave., which he had moved into two years earlier . </P> <P> Since 1900, Tesla had been living at the Waldorf Astoria in New York running up a large bill . In 1922, he moved to St. Regis Hotel and would follow a pattern from then on of moving to a new hotel every few years leaving behind unpaid bills . </P>

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