The US government has officially confirmed the existence of Area 51, and in that report, they state that it "was a test site for the military's U-2 spy planes." To be more specific: "The Central Intelligence Agency and Overhead Reconnaissance: The U-2 and OXCART Programs, 1954-1974." Continue reading for a 43-minute documentary that takes you inside the base.
Inside Area 51 - Full Documentary
What the documents do include, though, is a lot of interesting reading material about the U-2 program. Not only does it contain a full list of every pilot involved with the program, there is also information about how the British participated, along with specifics about several unmanned aerial reconnaissance missions.
A map of Area 51 is also included, along with accounts of some covert U-2 operations.