Well what about Area 51, most of the new technology for military aircrafts is tested overthere 
So if the Germans were able to build some kind of anti-gravity machine and the Americans took it, it can be easily transferred to Area 51, and maybe crashed during a testflight, cause it was a stormy day, maybe lightning hit them and they crashed
But I also read some books about UFOs in the past, books about Belgium, America, ....
And two military jets of the Belgian Airforce chased some kind of thing, a so called UFO, everytime when they had a Lock-on, it immediately flew the other direction, impossible for even the most modern jets and they had a breaklock
So I think UFOs exist, I also think aliens exist, but if they fit together this two terms, I don't know for sure, if they fit together than there is some kind of way to travel to this planet 
What about hyperspace and such?
Well I found a movie about some kind of interrogation of an alien at Area 51, but if it is true or not, I really don't know, and no, it is not those dissection on an alien, cause those one is fake, but maybe a real video, cause u see muscles move in those body and such
http://www.crowdedskies.com/alien_interogation.htm