The MythBusters head to a California mine to test an ancient Chinese military myth - a subterranean sonar system that could allegedly detect and intercept an invasion from below.
Adam and Jamie prepare to unleash the full MythBusters arsenal of weapons - pistols, shotguns, supersonic rifles and the ferocious, .50-calibre - in order to find out exactly how far underwater you have to swim to survive a gunshot from the surface.