Although the XF jet pilot Jim Cook was played by Jack Harris, the character's radio transmissions are voiced by Whit Bissell. Bissell also plays the Mission Team Manager in the episode.
Speaking as the test pilot, Whit Bissell pronounces "Mach 2" as "Match 2."
The X-F 190 experimental jet shown "crashing" at the beginning of the episode is actually a Convair F2Y Sea Dart landing on it's ski. It was the only supersonic seaplane ever built but was discontinued due to unsatisfactory performance.