U-2 Overflights of the Soviet Union
CIA Directorate of Science and Technology
2013
1956–1960
An internal history of the reconnaissance program that flew above Soviet air defenses — and, incidentally, generated a spike in UFO reports from airline pilots who had never seen anything cruise at 70,000 feet.
Why it was classified
It exposed the existence of Area 51, film-return imaging capability, and the fiction that Gary Powers' aircraft was a NASA weather plane.
Why it matters
The CIA's own historians concede the Air Force used UFO explanations as cover for U-2 sightings — official misdirection, documented in official records.