I believe in the existence of UFO's - just not ones that we've developed on our own since the 1940's. If an aircraft like the one in the video has been (or could be) developed, I'd be more inclined to believe it to be a product of alien technology transfer than postwar research and development. In other words, more like that scene in the movie "Independence Day" where the alien spacecraft is housed in the top-secret research facility for 50+ years.