16 " / 45 caliber Mark 6 gun The 16 " / 45 caliber Mark 6 gun was a naval gun designed in 1936 by the United States Navy for their Treaty battleships . It was first introduced in 1941 aboard their s , replacing the originally intended 14 " / 50 caliber Mark B gun s and was also used for the follow - up " South Dakota " class . These battleships carried nine guns in three triple turrets . The gun was an improvement to the 16 " / 45 caliber guns used aboard the , and the predecessor to the 16 " / 50 caliber Mark 7 gun used aboard the . Description . The 16 in / 45 were improved versions of the Mark 5 guns mounted on the s , with their limit of a shell with a maximum range at their turret limit of 30 degree elevation . A major alteration from the older guns was the Mark 6 ' s ability to fire a new armor piercing ( AP ) shell developed by the Bureau of Ordnance . At full charge with a brand - new gun , the heavy shell would be expelled at a muzzle velocity of 2 , 300 feet per second ( 701 m / s ) ; at a reduced charge , the same shell would be fired at 1 , 800 f / s ( 549 m / s ) . Barrel life — the approximate number of rounds a gun could fire before needing to be relined or replaced — was 395 shells when using AP , increasing to 2 , 860 for practice rounds . By comparison , the 12 " / 50 caliber Mark 8 gun of the large cruisers had a barrel life of 344 shots , while the 16 " / 50 caliber Mark 7 gun fitted in the s had a barrel life of 290 rounds . Turning at 4 degrees a second , each turret could train to 150 degrees on either side of the ship . The guns could be elevated to a maximum inclination of 45 degrees ; turrets one and three could depress to −2 degrees , but due to its superfiring position , the guns on turret two could only depress to 0 degrees . < ref name = " 16 / 45 " > DiGiulian , " United States of America 16 " / 45 ( 40 . 6 cm ) Mark 6 " < / ref > Each gun was long overall which is 45 bore diameters hence the 16 " / 45 caliber ; its bore and rifling length were and , respectively . Maximum range with the heavy AP shell was obtained at an inclination of 45 degrees : . At the same elevation a lighter high capacity ( HC ) shell would travel . The guns weighed 192 , 310 lb ( 87 , 230 kg ; 86 long tons ) not including the breech ; the turrets weighed slightly over 3 , 100 , 000 lb ( 1 , 410 , 000 kg ; 1400 long tons ) . When firing the same shell , the 16 in / 45 Mark 6 had a slight advantage over the 16 in / 50 Mark 7 when hitting deck armor — a shell from a 45 cal gun would be slower , meaning that it would have a steeper trajectory as it descended . At , a shell from a 45 cal would strike a ship at an angle of 45 . 2 degrees , as opposed to 36 degrees with the 50 cal . Shell . The Mark 6 and 7 guns were originally intended to fire the relatively light ( 1 . 00 long ton ) Mark 5 armor - piercing shell . However , the shell - handling system for these guns was redesigned to use the " super - heavy " APC ( Armor Piercing , Capped ) Mark 8 shell before any of the s were laid down . The large caliber guns were designed to fire two different 16 inch ( 406 mm ) shells : an armor piercing round for anti - ship and anti - structure work , and a high explosive round designed for use against unarmored targets and shore bombardment . The Mark 8 shells gave the " North Carolina " , " South Dakota " , and " Iowa " classes the second heaviest broadside of all battleship classes , despite the fact that the " North Carolina " and " South Dakota " ships were treaty battleship s . Only the super dreadnoughts could throw more weight . The Mark 6 ' s disadvantage relative to other contemporary battleship classes was its comparatively shorter range . The propellant consists of small cylindrical grains of smokeless powder with an extremely high burning rate . A maximum charge consists of six silk bags , each filled with 110 pounds ( 50 kg ) of propellant . Service history . The Mark 6 16 inch gun holds several distinctions relating to the United States ' World War II combat history . In the first instance , as the primary armament of these guns were employed against the Imperial Japanese Navy ' s during the Naval battle of Guadalcanal ; this has been cited by historians as the only instance in World War II in which one American battleship actually sank an enemy battleship . ( While there was a battleship versus battleship engagement at Leyte Gulf , torpedoes rather than gunfire were largely regarded as being responsible for sinking the enemy battleships . ) The " Washinton " had the aid of a fire control computer — in this case the Ford Instrument Company Mark 8 Range Keeper analog computer used to direct the fire from the battleship ' s guns , taking into account several factors such as the speed of the targeted ship , the time it takes for a projectile to travel , and air resistance to the shells fired at a target . This gave the US Navy a major advantage in the Pacific War , as the Japanese did not develop radar or automated fire control to a comparable level . " Washington " was able to track and fire at targets at a greater range and with increased accuracy , as was demonstrated in November 1942 when she engaged " Kirishima " at a range of at night . Using her nine 16 " / 45 caliber Mark 6 guns " Washington " fired 75 rounds of 16 " AP shells and scored an incredible twenty heavy caliber hits that critically damaged the " Kirishima " , which eventually sunk . During the same battle , " South Dakota " also fired off several salvos from her 16 " / 45 guns before she had to withdraw due to a faulty circuit breaker . In the second instance , the battleship employed these 16 " / 45 caliber guns as her primary armament , and she is believed to have to fired the United States ' first and last 16 inch shells of World War II ; the first use occurring 8 November 1942 during the Naval Battle of Casablanca ( shortly before the Naval battle of Guadalcanal ) , the last being 9 August 1945 off the coast of Hamamatsu , Japan . Furthermore , at Casablanca , this was the only time in the European theater that a fast battleship of the US Navy fired her guns in anger . Successor . The next US Navy battleship class , the , did not fall under Treaty weight restrictions and allowed for additional displacement . However , in their original design , the General Board was incredulous that a tonnage increase of would only allow the addition of s over the " South Dakota " s . Rather than retaining the 16 " / 45 caliber Mark 6 gun used in the " South Dakota " s , they ordered that future studies would have to include the more powerful ( but heavier ) 16 " / 50 caliber Mark 2 gun s left over from the canceled s and battleships of the early 1920s . It also allowed the draft of the ships to be increased , meaning that the ships could be shortened ( lowering weight ) and the power reduced ( since a narrower reduces drag ) . The Mark 2 50 - caliber gun weighed some more than the Mark 6 45 caliber did ; the barbette size also had to be increased so the total weight gain was about , putting the ship at a total of — well over the 45 , 000 long ton limit . An apparent savior appeared in a Bureau of Ordnance preliminary design for a turret that could carry the 50 caliber guns in a smaller barbette . This breakthrough was shown to the General Board as part of a series of designs on 2 June 1938 . Nonetheless , the Mark 7 gun still weighed about 239 , 000 pounds ( 108 000 kg ) without the breech , or 267 , 900 pounds with the breech , considerably heavier than the Mark 6 . The Mark 7 had a greater maximum range over the Mark 6 : vs . Interestingly , when firing the same conventional shell , the 16 " / 45 caliber Mark 6 gun used by the treaty battleships of the and es had a slight advantage over the 16 " / 50 caliber Mark 7 gun on the , when hitting deck armor — a shell from a 45 cal gun would be slower , meaning that it would have a steeper trajectory as it descended . At , a shell from a 45 cal would strike a ship at an angle of 45 . 2 degrees , as opposed to 36 degrees with the 50 cal . Barrel life — the approximate number of rounds a gun could fire before needing to be relined or replaced — was 395 shells when using AP , increasing to 2 , 860 for practice rounds . By comparison , the 12 " / 50 caliber Mark 8 gun of the large cruisers had a barrel life of 344 shots , while the 16 " / 50 caliber Mark 7 gun fitted in the s had a barrel life of 290 rounds . During World War II , the Mark 7 guns were only used for shore bombardment in the Pacific , while the Mark 6 guns also saw ship - to - ship combat in both the Pacific and European theaters . This was attributed to the fact that ships mounting the Mark 7 batteries , the , were commissioned later than the Mark 6 - equipped and es , so they missed the Naval Battles of Casablanca and the Guadalcanal , one of the few instances where the US Navy ' s fast battleships were deployed for ship - to - ship combat . Most large scale naval battles involving the US Navy were fought by carrier - based aircraft in the Pacific .