 The original design called for eighteen 5 " / 51 caliber guns . These guns were originally mounted on the Florida- and Wyoming @-@ class battleships , but they found their way into the secondary armament of every U.S. battleship that was built prior to the Washington Naval Treaty . Also , many of the destroyers , submarines , and auxiliaries that were built during this time mounted this gun as their main gun . They fired a 50 @-@ pound ( 23 kg ) shell at a muzzle velocity of 3 @,@ 150 fps ( 960 mps ) and a rate of eight or nine rounds per minute to a range of 18 @,@ 880 yards ( 17 @,@ 260 m ) at an elevation of 25 degrees . 
