I'm surprised that nobody has yet mentioned Boeing's SST effort. It was a much more ambitious aircraft, larger and faster. Prototypes were under construction.

I'm surprised that nobody has yet mentioned Boeing's SST effort. It was a much more ambitious aircraft, larger and faster. Prototypes were under construction. There were orders for 122 planes. Development was expensive, and Boeing was relying on considerable contributions from the US government. The project was cancelled in 1971 amid cost and environmental concerns. https://en.wikipedia.org/wiki/Boeing_2707 https://en.wikipedia.org/wiki/Boeing_2707