The technique of creating air bubbles around underwater projectiles to vastly reduce skin friction drag through the water.
This remarkable anti-ship weapon would run an innovative boron-powered ramjet engine that works in both air and water. Supersonic in the air and supercavitating under the water, it could strike farther and faster than any conventional torpedo.
Regular bullets decelerate so quickly in water that they only make it a few feet. But Norway's DSG has used the drag-reducing abilities of supercavitation to produce some extraordinary projectiles that'll hit submerged targets up to 200 feet away.