The 6"/53 caliber gun (spoken "six-inch-fifty-three-caliber") formed the main battery of United States Navy light cruisers and submarine cruisers built during the 1920s. United States naval gun terminology indicates the gun fired a projectile 6 inches (15 cm) in diameter, and the barrel was 53 calibers long (barrel length is 6 inch x 53 = 318 inches or 8 meters.) The gun with side swing Welin breech block and Smith-Asbury mechanism weighed about 10 tonnes and used a silk bag containing 44-pounds (20 kg) of smokeless powder to give a 105-pound (47.6 kg) projectile a velocity of 3000 feet per second (900 m/s). Early Marks were built-up guns with a liner, tube, full-length jacket, and 2 hoops; but the Mark 14 gun was of monobloc construction. Useful life expectancy was 700 effective full char