Mark Schaeffer wrote:
[...]


The A-12 was the first aircraft to reach Mach 3 and return in one
piece.


[...]

What are the dates for A-12 and X-15 first flying at Mach 3.0+?

Mark

A-12 was about 20 July 1963. I've interviewed Jim Eastham and
he claims to be the first. Lou Schalk was two days later. Norm
Nelson backed up Jim's claim and said that he'd tried to persuade
Schalk and Bill Park that an increase of 0.1 Mach number per flight
was much too conservative, but they wouldn't listen. Eastham did.