The authors of the CIA history, Gregory Pedlow and Donald Welzenbach, said the site was nicknamed "Paradise Ranch," or simply the Ranch, to make it sound more attractive to the test project's workers. The first U-2 test flight took place at Area 51 on Aug. 4, 1955, and over the years that followed, the site was used for training U-2 pilots.
The Groom Lake facility was also used for development of the U-2 spy plane's successors, including the Lockheed A-12 Oxcart and the D-21 Tagboard. Later on, Area 51 served as a test site for the F-117 stealth fighter. To this day, the area surrounding the facility has been closely guarded, and the airspace is off-limits to civilian air traffic.
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Such high levels of secrecy, combined with the occasional sightings of strange aircraft, have fueled UFO tales for decades. For example, in a 2011 book titled "Area 51," investigative journalist Annie Jacobsen quoted her sources as saying that wreckage from the Roswell UFO incident ended up at Area 51 for study.
As one would expect, the CIA book makes no mention of Roswell or alien spacecraft.
—By Alan Boyle, NBC News