Abstract: 1. A device including an expendable cartridge-barrel assembly comprising a cartridge casing forming a barrel, the wall thickness of said barrel being at least equal to about the diameter of the bore therein, a retainer affixed to and rearwardly of said casing, a high energy propellant enclosed within said assembly, a primer within said retainer and communicating with said propellant, a projectile frictionally fitted within and extending along the bore of said barrel and having a rear end in proximate relation to said propellant, said projectile being designed for high sectional density and minimum drag with water, and a watertight seal affixed to a front end of said cartridge-barrel assembly.