Lockheed SR-71 Blackbird - Origins and Evolution

One of the world's most extreme and enigmatic aircraft, the Lockheed SR-71 Blackbird, is the ultimate evolution of a long line of top secret projects which first coalesced in the form of the CIA's A-12 reconnaissance platform. American aircraft development specialist Scott Lowther looks in detail at the vast range of different variants and configurations proposed for this remarkable family of high-speed high-altitude jets.