3 " / 50 caliber gun The 3 " / 50 caliber gun ( spoken " three - inch - fifty - caliber " ) in United States naval gun terminology indicates the gun fired a projectile 3 inches ( 7 . 62 cm ) in diameter , and the barrel was 50 caliber s long ( barrel length is 3 " x 50 = 150 " or 3 . 81 meters ) . Different guns ( identified by Mark numbers ) of this caliber were used by the U . S . Navy and U . S . Coast Guard from 1890 through the 1990s on a variety of combatant and transport ship classes . Earlier guns . The US Navy ' s first 3 " / 50 caliber gun ( Mark 2 ) was an early model with a projectile velocity of per second . Low - angle mountings for this gun had a range of 7000 yards at the maximum elevation of 15 degrees . The gun entered service around 1902 with the Bainbridge - class destroyer s , and was also fitted to Connecticut - class battleship s . By World War II these guns were found only on a few Coast Guard cutters and Defensively Equipped Merchant Ships . Low - angle 3 " / 50 caliber guns ( Marks 3 , 5 , 6 , and 19 ) were originally mounted on ships built from the early 1900s through the early 1920s , and were carried by submarines , auxiliaries , and merchant ships during the second world war . These guns fired the same per second ammunition used by the following dual purpose Marks , but with range limited by the maximum elevation of the mounting . These were built - up gun s with a tube , partial - length jacket , hoop and vertical sliding breech block . Dual - purpose 3 " / 50 caliber guns ( Marks 10 , 17 , 18 , and 20 ) first entered service in 1916 as a refit to the USS Texas ( BB - 35 ) and were subsequently mounted on many types of ships as the need for anti - aircraft protection was recognized . During World War II , they were the primary gun armament on destroyer escort s , patrol frigate s , submarine chaser s , minesweeper s , some fleet submarine s , and other vessels , and were a secondary dual - purpose gun on some other types of ships , including some older battleships . They also replaced the original low - angle 4 " / 50 caliber gun s ( Mark 9 ) on " flush - deck " Wickes and Clemson class destroyer s to provide better anti - aircraft protection . The AVD seaplane tender conversions received 2 guns ; the APD transport , DM minelayer , and DMS minesweeper conversions received 3 guns , and those retaining destroyer classification received 6 . These guns used fixed ammunition ( case and projectile handled a single assembled unit ) weighing 34 pounds . Projectile s weighed about 13 pounds including a burster charge of 0 . 81 pounds for Anti - aircraft ( AA ) rounds or 1 . 27 pounds for High Capacity ( HC ) rounds . Maximum range was 14 , 600 yards at 45 degrees elevation and ceiling was at 85 degrees elevation . Useful life expectancy was 4300 effective full charge s ( EFC ) per barrel . Cold War anti - aircraft gun . The 3 " / 50 caliber gun ( Mark 22 ) was a semiautomatic anti - aircraft weapon with a power driven automatic loader . The United States Navy considered contemporary 5 " / 38 caliber gun s and 5 " / 54 caliber guns more effective against surface targets . These monobloc 3 " guns were fitted to both single and twin mountings . The single was to be exchanged for a twin 40 mm antiaircraft gun mount and the twin for a quadruple 40 mm mount . This was performed on Essex - class aircraft carrier s , Sumner - and Gearing - class destroyer s and other ships circa 1946 - 50 . Although intended as a one - for - one replacement for the 40 mm mounts , the final version of the new mounts was heavier than expected , and on most ships the mounts could be replaced only on a two - for - three basis . The mounts were of the dual purpose , open - base - ring type . The right and left gun assemblies were identical in the twin mounts . The mounts used a common power drive that could train at a rate of 30 degree / second and elevate from 15 degrees to 85 degrees at a rate of 24 degree / second . The cannon was fed from an on mount magazine which was replenished during action by two loaders on each side of the cannon . With proximity fuze and fire - control radar , a dual 3 " / 50 mount firing 20 rounds per minute per barrel was considered more effective than a quad Bofors 40 mm gun against subsonic aircraft , but relatively ineffective against supersonic jets and cruise missiles . Destroyers that were modernized during the Fleet Rehabilitation and Modernization ( FRAM ) program of the 1960s had their guns removed , but others retained them . In 1992 , the USCGC Storis ( WMEC - 38 ) 3 " / 50 caliber main battery was removed from the cutter . This was the last 3 " / 50 caliber gun in service aboard any US warship . The gun is still in service , however , on some warships of the Philippine Navy , including BRP Rajah Humabon ( PF - 11 ) , formerly USS Atherton ( DE - 169 ) . The 17 Asheville - class gunboat s mounted a single 3 " / 50 Mk 34 as their primary armament .