The CIA created Area 51 in 1955 to test and develop top secret U.S. military projects in the remote Nevada desert. More than 50 years later, the base still doesn't officially exist and appears on no public U.S. government maps.
In the 1950s and '60s, Area 51 was the epicenter of the OXCART project, intended to create the successor for the U-2 spy plane.
The OXCART plane was expected to be undetectable in the air as it flew surveillance and information-gathering missions over the Soviet Union. But Area 51 personnel soon found it necessary to conceal the craft from the Soviets eyes even when it was still being tested on the ground.