In the 1940's a program code-named: Silver Bug, to build Vertical landing/takeoff aircraft, by the USAF. The main design for this aircraft was designed by a NAZI Scientist who defected after WWII, the design was disk-shaped.
Apparently NAZIs captured a downed UFO and based there designs on this but never got past the drawing board. Later the defecting scientist went to the US.
The resulting plans are as below (left to right):
Base Plan of UFO under blue glass to enhance image.
The above pictures patterns share a likeness. Thus this plan of a UFO probably isn't a hoax at all, but credible.
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