When classified planes were being built in Area 51, the Soviet Union's spy satellites made out their shapes the same way people can tell if a car has been parked in a certain space on a hot day.
Regardless of what else has been housed at Area 51, the OXCART project found a home there in the late 1950s. OXCART's team was building a spy plane that would succeed the U2. During these tests, scientists rolled prototype planes along stretches of asphalt and checked to see if they could duck radar. Those that showed up on radar were scrapped, and the designs that went by unseen were refined.
