Area 51
There was intense secrecy surrounding the base. The U.S. government did not acknowledge its existence until July 14, 2003. This secrecy made it the frequent subject of fiction and conspiracy theories and a central component to unidentified flying object (UFO) folklore. Testing the U-2 plane in the 1950s – at altitudes much higher than commercial aircraft then flew – provoked "a tremendous increase in reports of unidentified flying objects (UFOs)".