The Aliens haven't been back for a while? I mean how else do you explain the SR-71 8^)
To build craft like the SR-71 it took officers with a mission orientation and vision to find the funding, hide it from the generals, and find the right people to implement a workable design and plan. The SR-71 was black and largely but secretly backed by the intelligence agencies. The line generals at the time were no more inclined to spend time and funding on an aircraft that didn’t dogfight or drop iron bombs than they are today.
The Navy equivalent at about the same time was the Poseidon system development. The admirals wanted nothing to do with launching ICBMs from Naval platforms.