For decades, a U.S. military installation located roughly 100 miles (161 kilometers) north of Las Vegas had been one of the worst-kept secrets on the planet. Area 51, as it's commonly known to UFO conspiracy theorists and aviation buffs who piece together the details of classified military spy plane prototypes, is a place whose existence the U.S. government long refused even to acknowledge.
But in August 2013, the shroud over Area 51 finally lifted, at least a bit. Jeffrey T. Richelson, a researcher at the Washington, D.C.-based National Security Archive, a nonprofit think tank, obtained declassified documents about the development and use of the U-2 and OXCART surveillance aircraft in the 1950s and 1960s. The documents made repeated references to Area 51 and detailed how it was selected as a testing area by the CIA, the U.S. Air Force and defense contractor Lockheed because of its remote location. They even included a map that confirmed its exact location [source: National Security Archive].