The Mk12 5 inch, 38 caliber gun was one of the triumphs of American naval weaponry from World War Two. First used in 1934, it remained a standard weapon on new vessels until 1948. It used a 55 lb shell with a separate case that was manually loaded but power-rammed, allowing a high rate of fire from -15 to +85 degree angles of elevation. Coupled with the sophisticated fire control computers in US warships, it was one of the most effective anti-aircraft weapons in US inventory even before the introduction of radar proximity-fused shells in 1943. More than 8,000 of these guns were built by the end of World War Two, fitted to everything from merchant mariners to battleships like the USS New Jersey.
Source: America's Do – It – All Naval Gun: The 5 Inch Mk12 on the USS New Jersey
