YF-12A

The YF-12A is the prototype for a proposed fighter jet, the F-12, derived from the CIA's A-12 reconnaissance plane, and related to the SR-71 Blackbird.

NASA's Mach 3+: NASA/USAF YF-12 Flight Research, 1969-1979 [direct link to 9.8 megabyte PDF] contains information about the development of the Blackbird family, the YF-12 development program, and of course the YF-12's career as a high-speed, high-altitude test platform with NASA.

The YF-12A displayed by the museum is the only remaining example still in YF-12A configuration (another YF-12A was converted to be an SR-71C).