@pirate @ttyymmnn @facw @f86sabre I'm rather dubious of the
WW2 pilots that claimed to have taken P38s or P51s supersonic. While propellers can be made to turn at supersonic speeds, as with the Tu-95 Bear and XF-84 Thunderscreech, a prop also becomes a rather effective speedbrake the faster the plane its attached to is going.
The XF-88B, powered by both a turboprop and two afterburner-equipped J34 jets, was able to approach Mach 0.9 in level flight, and reached 1.02 in a dive, but was unable to do so twice in one flight, which was needed for FAI certification.
The Tu-95 (and the Tu-114 airliner based on it) can hit 606 mph in level flight, but has not been subjected to an FAI recognized course.
On 6 Feb 2003 a Piaggio Avanti flew from Fort Worth to Atlanta, attaining an average speed of 576.3mph and earning the FAI's record for fastest propeller-driven aircraft.
Supposedly a Spitfire hit Mach 0.92 in 1944, BUT
It was in a dive
The propeller had broken off
So that's doubly questionable.
I don't think that the P-38 ever went supersonic. What I'm saying is that through my own research, I think they got terrifyingly close, at least to the point where stuff started coming apart (for example, that link above mentions tail assemblies coming off of planes who went a wee bit too fast in a dive), with the entire point being that I also think that it was a bit easier for jets around that era to have beaten Yeager to the sound barrier.