Comment by dingaling
18 hours ago
It's also largely PR guff. The first privately-developed supersonic aircraft was the Northrop N-156F, forerunner of the F-5, that first flew in 1959. Funded entirely from company funds with no military contract. And it went supersonic in its first flight with no drama.
In fact the chase plane for the Boom XB-1 is a T-38, derived from the N-156F. It can outrun the XB-1.
I'm not sure how strictly privately developed the N-156F is given you could easily argue that reuse of design, knowledge and relationships from existing contracts saved them a lot of money.