Area 51  is a military installation located at Groom Lake in southern Nevada. It is administered by  Air Force Base in southern California. The installation has been the focus of numerous conspiracies involving extraterrestrial life, though its only confirmed use is as a flight testing facility.

For years there was speculation about the installation, especially amid growing reports of UFO sightings in the vicinity. The site became known as Area 51, which was its designation on maps of the Atomic Energy Commission. Conspiracy theories gained support in the late 1980s, when a man alleging to have worked at the installation claimed that the government was examining recovered alien spacecraft.

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What Is Known (and Not Known) About Area 51

Area 51 has spawned more conspiracy theories than perhaps any other military facility in the world. Here’s what we know…

In 2013 the U.S. government officially acknowledged the existence of Area 51. That year the National Security Archive at the George Washington University obtained through the Freedom of Information Act (FOIA) a formerly classified CIA document that chronicled the history of the U-2 spy plane; a heavily redacted version had previously been released in 1998. According to the report, in 1955 the remote site—which included an airfield not used by the military since World War II—was selected in order to test the U-2. Test flights of that spy plane, and subsequent aircraft, accounted for many of the UFO sightings in the area; the U-2 could reach altitudes much higher than any other planes at the time. After the U-2 was put into service in 1956, Area 51 was used to develop other aircraft, including the A-12 (also known as OXCART) reconnaissance plane and the stealth fighter F-117 Nighthawk.