Cc, sound barrier alot higher then 480. There were stories about some WW2 planes who broke the sound barrier in dives, the pilots didn't live to tell about it though. RAF did alot of tests after the war, they took Griffon Spitfires, climbed like hell and then dove em straight down, most of the pilots who did this died, without reaching teh sound barrier. Allmost all, if not all planes got wrecked.