Though you can see the Area 51 complex’s buildings in satellite images, it doesn’t appear on any public U.S. government maps. For decades, conspiracy theorists and UFOlogists have speculated that the government uses the secret Nevada site to experiment with extraterrestrials and their spacecrafts. 

Some have connected the site with the alleged government coverup of a 1947 incident in which an alien spacecraft supposedly crashed near Roswell, New Mexico. Others have even claimed that the moon landing was staged right there in the Nevada desert. Skeptics may find all this hard to believe—but if it’s not true, then what really goes on at Area 51?

Over the years, the CIA, U.S. Air Force and aerospace company Lockheed Martin have all used Area 51 as a staging ground for test flights of experimental aircraft (a.k.a. “black aircraft”). According to documents declassified in 2007, in the 1950s and 1960s Area 51 was home to a top-secret Cold War-era program known as Oxcart, which aimed to develop a spy plane that would be undetectable in the air and could be used for information gathering missions behind the Iron Curtain

The Archangel-12 was eventually developed at Area 51. The A-12 could travel at speeds of more than 2,000 miles an hour and take clear pictures of objects on the ground from an altitude of 90,000 feet. Other well-known aircraft tested there include the A-12’s successor, the SR-71 Blackbird, as well as the F-117 Nighthawk stealth fighter. 

In the late 1960s, at the height of the Vietnam War, personnel began evaluating covertly obtained foreign aircraft at Area 51. Test pilots flew these “found” aircraft—or their reverse-engineered re-creations—in mock sorties in and around the airspace of the Nevada site.

From the ground, experimental aircraft traveling at Mach-3 speeds undoubtedly resembled some people’s idea of what alien spacecraft would look like, helping to explain why so many people reported UFO sightings in the skies above Nevada over the years. Such sightings—along with the secrecy surrounding the Groom Lake site—fueled the rumors swirling around Area 51, and helped create the air of mystery it retains today.