CIA/CSI/ History Staff Monograph, The Central Intelligence Agency and Overhead Reconnaissance: The U-2 and Oxcart Programs, 16 July 2002.

This is a CIA History Staff monograph by Gregory W. Pedlow and Donald E. Welzenbach, written in 1992 and approved for release in 2011. It covers the CIA's manned overhead reconnaissance program from 1954 to 1974 and its two aircraft, the U-2 and the A-12 OXCART. It follows their development, the overflights of the Soviet Union, the downing of Francis Gary Powers in 1960, and later operations. One section is titled "U-2s, UFOs, and Operation BLUE BOOK."

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within 30 miles of South Vietnam, all of Laos south of Paksane, and
all of North Vietnam within 30 miles of South Vietnam or the coast.
The remaining portions of Indochina remained the responsibility of
the Agency's U-2s. Then in August 1964, following the Gulf of
Tonkin Resolution, the Air Force assumed responsibility for all of
Indochina.45
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