Chuck Yeager is credited with being the first pilot to break the speed of sound but that record has since been modified to include the caveat, “in level flight”. The reason for this is that a German Me-262 pilot is acknowledged to have broken the sound barrier during the war, but did so while diving his plane.
That is still disputed. The 262 had compressibilty problems at mach .86 and the pilot would lose control.
I thought it was the ME-163 rocket fighter.
I believe a British test pilot post-WWII may have also broken the sound barrier in his jet, since his flight caused a sonic boom followed shortly by another boom as the plane crashed after control surfaces were locked by going supersonic.
It’s certainly possible that the ME-262 could have exceeded the Speed of Sound in a dive (though how it would have been recoverable is a major question). But aviation records require verification and as we say in Scuba diving, “If you didn’t get a picture, it didn’t happen.”
The event you are referring to wasn't recognized because there was no instrumentation to verify the claim.
Gen Robin Olds claimed he took a P-38 supersonic in a dive. The plane was known to approach mach 1 because of compressibility issues killing pilots diving the plane.
"Wheaties" Welch claimed to dive an F-86 through mach 1 and probably did not once but twice. The second time was only hours before Gen Yeager's historic flight.
Welch then went on to take the F-100 supersonic as the first jet powered US production aircraft to do that in level flight. Later in that test program, the plane killed him when he over G'd it and it disintegrated. The irony was that his chase pilot was Chuck Yeager.