Supercavitating torpedoes can reach extreme underwater speeds by travelling inside a gas-filled cavity that sharply reduces their contact with water.
Beyond torpedoes, supercavitating projectiles can streak through the water at blistering speeds to intercept naval mines, incoming torpedoes and unmanned underwater vehicles, and even combat divers.
Now, Chinese engineers are applying a related drag-reduction principle to commercial shipping, with a bubble-lubrication system cutting net energy consumption.