3″/50 caliber gun


 * For Army 3-inch gun see 3-inch M1918 gun

The 3″/50 caliber gun (spoken "three-inch-fifty-caliber") in United States naval gun terminology indicates the gun fired a projectile 3 in in diameter, and the barrel was 50 calibers long (barrel length is 3 in × 50 = 150 in). 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 2100 ft 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 destroyers, and was also fitted to Connecticut-class battleships. 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 2700 ft 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 guns 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 escorts, patrol frigates, submarine chasers, minesweepers, some fleet submarines, 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 guns (Mark 9) on "flush-deck" Wickes and Clemson class destroyers 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.  Projectiles 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 29800 ft at 85 degrees elevation.  Useful life expectancy was 4300 effective full charges (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 guns 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 carriers, Sumner- and Gearing-class destroyers 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 3 in 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 3 in 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 gunboats mounted a single 3″/50 Mk 34 as their primary armament.

Ships mounting 3″/50 caliber Mark 22 guns

 * s (built with 10 twin mounts)
 * s (built with 2 single and 11 twin mounts)
 * USS Juneau (CL-119) (built with 7 twin mounts)
 * Ashtabula-class oiler (built with 4 single mounts)
 * s (FRAM up to 20 guns)
 * s (FRAM up to 12 guns)
 * s (FRAM up to 20 guns)
 * s (FRAM up to 6 guns)
 * Allen M. Sumner-class destroyers (FRAM up to 6 guns)
 * Gearing-class destroyers (FRAM up to 6 guns)
 * Terrebonne Parish-class tank landing ships (built with 3 twin mounts)
 * s (built with 2 twin mounts)
 * Neosho-class oilers (built with 4 or 6 twin mounts)
 * Dealey-class destroyer escorts (built with 1 twin and 2 single mounts)
 * Thomaston-class dock landing ships (built with 6 twin mounts)
 * s (built with 2 twin mounts)
 * Forrest Sherman-class destroyers (built with 2 twin mounts)
 * USS Tulare (LKA-112) (built with 6 twin mounts)
 * Suribachi-class ammunition ships (built with 2 twin mounts)
 * De Soto County-class tank landing ships (built with 3 twin mounts)
 * Claud Jones-class destroyer escorts (built with 2 single mounts)
 * Coontz-class frigates (built with 2 twin mounts)
 * s (built with 4 twin mounts, some reduced to 2 mounts to provide space for missile launchers)
 * USS Bainbridge (CGN-25) (built with 2 twin mounts)
 * Leahy-class cruisers (built with 2 twin mounts)
 * Raleigh-class amphibious transport docks (built with 4 twin mounts)
 * Bronstein-class frigates (built with 1 twin and 1 single mount)
 * Mars-class combat stores ships (built with 4 twin mounts)
 * s (built with 2 twin mounts)
 * Belknap-class cruisers (built with 2 single mounts)
 * Sacramento-class fast combat support ships (built with 4 twin mounts)
 * Austin-class amphibious transport docks (built with 4 twin mounts)
 * USS Truxtun (CGN-35) (built with 2 single mounts)
 * Charleston-class amphibious cargo ships (built with 4 twin mounts)
 * Kilauea-class ammunition ships (built with 4 twin mounts)
 * s (built with 4 twin mounts)
 * Anchorage-class dock landing ships (built with 4 twin mounts)
 * s (built with 2 twin mounts)
 * Blue Ridge-class command ships (built with 4 twin mounts)