Area 51

A top-secret air base in Nevada. Declassified CIA histories show it was used to test spy planes such as the U-2, and its secrecy made it central to UFO folklore.

Wikipedia says all research at Area 51 is classified Top Secret/Sensitive Compartmented Information. The CIA acknowledged the base publicly on 25 June 2013, in response to a FOIA request lodged in 2005, and has since declassified papers on its history and purpose. Wikipedia adds that the secrecy has made the base a regular target for conspiracy theories and a core part of UFO folklore.

The release followed a FOIA request from the National Security Archive, which received a less redacted copy of the CIA's internal history of its Oxcart and U-2 reconnaissance programmes. CNBC and NBC News summed it up: the base's mission was testing spy planes, the U-2 among them, and studying UFOs was no part of it. National Geographic says the Air Force and the CIA spent decades there developing advanced spy planes, among them the A-12 and the U-2.

Several sources tie the base's UFO reputation to those flights. In a 1997 history for the CIA, Gerald Haines wrote that U-2s often looked like fiery objects to people on the ground, and that Blue Book investigators traced many sightings to these flights while telling the public they were ice crystals or temperature inversions. National Geographic says sightings of these aircraft probably fed rumours of alien visitors, and that a Pentagon investigation suggests the Air Force itself may have kept the UFO myths going.