Roswell Incident
It is alleged that on July 6 1947, near the US base at Roswell New Mexico, a flying saucer crashed. Film exists of the dissection of an alien being (could it be a fake?), said to come from this crash. To those who like a conspiracy theory, it seems perfectly logical that the US government would hush up the crash in the hope that they could make use of the flying saucer technology to give them total supremacy in warfare. If this is the case, they've been pretty darned slow.