Although hard evidence is a little sketchy, another theory floats about in the conspiratorial ether. A 1994 book entitled "The Rainbow Conspiracy" by Brad Steiger quotes a man named Vladimir Terziski, author of another book, "Close Encounters of the Kugelblitz Kind". According to Steiger, Terziski "maintains that antigravity research began in the 1920s with the first hybrid antigravity circular craft, the RFZ-1, constructed by the secret Vrill society".
Also a man named W. A. Harbinson wrote a novel he claimed was based upon fact, "Genesis: Project Saucer, Part II" which featured an appendix containing results of his research linking the "foo fighters" spotted by US wartime pilots with German designers. Harbinson also linked SS founder Heinrich Himmler with the secret "saucer" projects, and on a similar vein, Max Amann, one of Hitler's oldest friends and controller of the Nazi Party's publishing system, was also known to have been affiliated with a secret group called the Society of the Vrill.
Whatever the source, stories abound which suggest that the Nazis did indeed endeavour to develop a highly maneouvrable antigravity based weapon. As we know, after the war ended, many German scientists were captured and taken back to America under Project Paperclip where they were put to work for the military. It is not inconceivable that they passed on their research to the US army who developed it further and who still work to perfect it. The popularity of the idea of alien spacecraft and abductions would obviously be encouraged because it merely draws the attention away from the truth, which is out there.