That's not an accurate description at all. Both the SR-71 and the YF-12 were developed from the A-12, which was purely a reconnaissance aircraft: https://en.wik

That's not an accurate description at all. Both the SR-71 and the YF-12 were developed from the A-12, which was purely a reconnaissance aircraft: https://en.wikipedia.org/wiki/Lockheed_A-12 https://en.wikipedia.org/wiki/Lockheed_A-12 The whole concept of using the "Blackbird" family of planes as interceptors was an experimental offshoot that was quickly cancelled, the SR-71 certainly wasn't developed as some byproduct of an interceptor, it it was the other way around, the interceptor was a failed offshoot of the reconnaissance aircraft.