|3-inch/50 caliber gun (Mk 22)|
|Place of origin||United States|
|In service||1890-1994 (US Navy)|
|Used by||US Navy|
|Variants||Marks 2, 3, 5, 6, 8, 10, 17, 18, 19, 20, 21, and 22|
|Shell||complete round: 24 lb (11 kg); projectile weight: 13 lb (5.9 kg) projectile types: AP, AA (with VT proximity fuze), HE, Illumination|
|Caliber||3-inch (76 mm)|
|Rate of fire||15 – 20 rounds per minute|
|Muzzle velocity||2,700 ft/s (820 m/s)|
|Maximum firing range||
|Sights||Peep-site and Optical telescope|
The 3"/50 caliber gun (spoken "three-inch fifty-caliber") in United States naval gun terminology indicates the gun fired a projectile 3 inches (76 mm) in diameter, and the barrel was 50 calibers long (barrel length is 3 in × 50 = 150 in or 3.8 m). 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.
The US Navy's first 3"/50 caliber gun (Mark 2) was an early model with a projectile velocity of 2,100 feet (640 m) per second. Low-angle (single-purpose/non anti-aircraft) mountings for this gun had a range of 7000 yards at the maximum elevation of 15 degrees. The gun entered service around 1900 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 2,700 feet (820 m) 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 1915 as a refit to 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 auxiliary vessels, and were used as a secondary dual-purpose battery 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 gun was also used on specialist destroyer conversions; the "AVD" seaplane tender conversions received two guns; the "APD" high-speed transports, "DM" minelayers, and "DMS" minesweeper conversions received three guns, and those retaining destroyer classification received six.
These dual-purpose guns were "quick-firing", meaning that they used fixed ammunition, with powder case and projectile permanently attached, and handled as a single unit weighing 34 pounds (as opposed to older guns and/or heavier guns, in which the shell and powder are handled and loaded separately, which reduces the weight of each handled component, but slows the loading process). The shells alone weighed about 13 pounds including an explosive bursting charge of 0.81 pounds for anti-aircraft (AA) rounds or 1.27 pounds for High Capacity (HC) rounds, the remainder of the weight being the steel casing. Maximum range was 14,600 yards at 45 degrees elevation and ceiling was 29,800 feet (9,100 m) at 85 degrees elevation. Useful life expectancy was 4300 effective full charges (EFC) per barrel.
The 3"/50 caliber gun Marks 17 and 18 was first used as a submarine deck gun on R-class submarines launched in 1918–1919. At the time it was an improvement on the earlier 3"/23 caliber gun. After using larger guns on many other submarines, the 3"/50 caliber gun Mark 21 was specified as the standard deck gun on the Porpoise- through Gato-class submarines launched in 1935–1942. The small gun was chosen to remove the temptation to engage enemy escort vessels on the surface. The gun was initially mounted aft of the conning tower to reduce submerged drag, but early in World War II it was shifted to a forward position at the commanding officer's option. Wartime experience showed that larger guns were needed. This need was initially met by transferring 4"/50 caliber guns from S-class submarines as they were shifted from combat to training roles beginning in late 1942. Later, the 5"/25 caliber gun, initially removed from battleships sunk or damaged in the attack on Pearl Harbor and later manufactured in a submarine version, became standard.
When it was found that multiple hits from Oerlikon 20 mm cannon and Bofors 40 mm guns were unable to prevent kamikaze strikes during the final year of the Second World War, the 3"/50 was adopted as a replacement for these weapons.
The 3"/50 caliber gun (Mark 22) was a semiautomatic anti-aircraft weapon with a power-driven automatic loader and were fitted as single and twin mounts. The single was to be exchanged for a twin 40 mm antiaircraft gun and the twin for a quadruple 40 mm mount, on Essex-class aircraft carriers, Allen M. Sumner and Gearing-class destroyers. Although intended as a one-for-one replacement for the 40 mm mounts, the new 3-inch (76 mm) mounts were heavier than expected and on most ships, the mounts could only be replaced on a two-for-three basis. The mounts were of the dual purpose, open-base-ring type and the right and left gun assemblies were identical. The mounts used a common power drive that could train at a rate of 30 degrees/second and elevate from 15 degrees to 85 degrees at a rate of 24 degrees/second. The cannon was fed automatically from an on-mount magazine which was replenished by two loaders on each side of the cannon.
With proximity fuze and fire-control radar, a twin 3"/50 mount firing 50 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-inch (76 mm) guns removed. Experimentation with an extended range variant (3"/70 Mark 26 gun) was abandoned as shipboard surface-to-air missiles were developed. The United States Navy considered contemporary 5"/38 caliber guns and 5"/54 caliber Mark 42 guns more effective against surface targets. In 1992, the 3"/50 caliber main battery on USCGC Storis was removed and was supposedly the last 3"/50 caliber gun in service aboard any US warship although US Navy Charleston-class amphibious cargo ships retained their forward mounts until, USS El Paso (LKA-117) was decommissioned in 1994. The gun is still in service on warships of the Philippine Navy.
The 17 Asheville-class gunboats mounted a single 3"/50 Mk 34 as their primary armament.
YouTube title: USS Salem Rapid Fire Guns
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