Hm. It seems the U.S. government did fly flying saucers out of Area 51 after all. If this story is to be believed (and I think it is), Area 51 was the home base for a top-secret spy plane named OXCART which had a large disc-like fuselage to carry fuel. Information about the program is just now becoming public because the records are being declassified as they become fifty years old.
Not quite as cool as reverse-engineered alien technology, but pretty cool nonetheless.