Stingray - Season 1 Episode 19 Deep Heat

Investigating the disappearance of a robot probe, Stingray is drawn to the bottom of a volcano where two survivors of a destroyed city attempt to steal Stingray to escape the erupting volcano. When Marina locks the hatch they are forced to return for Troy and Phones who have been left to die. Since there are only two sets of breathing gear, Troy and Phones must rely on their WASP training to make the swim to Stingray.