Weapons

The Mark 12 5"/38 caliber gun was mounted on a large number of US Navy ships during the World War II era. The ability to project force while miles at sea has always been a key ingredient to the success of modern warships. Using their 5 inch guns, such ships had the ability to fire a 55 lb. projectile over 9 miles. This, in fact, occurred in supporting U.S. Marine Corp ground troops during the Guadalcanal campaign, fought between 7 August 1942 and 9 February 1943.

The Mark 12 5"/38 caliber gun was a United States naval gun. The gun was installed into Single Purpose and Dual Purpose mounts. On these 5" mounts, Single Purpose (SP) means that the mount was limited to 35° elevation with no provision for AA shell fuze setters, and is designed to fire at surface targets only. Dual Purpose (DP) means that it is designed to be effective against both surface and aircraft targets because it can elevate to 85° and has on mount AA shell fuze setters.

United States naval gun terminology indicates the gun fired a projectile 5 inches (127mm) in diameter, and the barrel was .38 calibers long. The rate of fire for the MK 38 mount was typically 15 rounds per minute. The comparatively high rate of fire for a gun of its caliber earned it an enviable reputation, particularly as an anti-aircraft weapon, a role in which it was commonly employed by United States Navy vessels.

Among naval historians, the 5"/38 gun is considered the best intermediate-caliber, dual purpose naval gun of World War II, especially as it was usually under the control of the advanced Mark 37 Gun Fire Control System which provided accurate and timely firing solutions against surface and air targets. Even this advanced system required nearly 1000 rounds of ammunition expenditure per aircraft kill. However, the planes were normally killed by shell fragments and not direct hits; barrage fire was used, with many guns firing in the air at the same time. This would result in large walls of shell fragments being put up to take out one or several planes or in anticipation of an unseen plane, this being justifiable as one plane was capable of significant destruction.

The open single pedestal mount was the first 5"/38 cal type installed on navy ships. Since these mounts did not have Upper Handling Rooms [a base ring stand that had an ammunition handling room below the mount], they could be installed on ships without extensive reconstruction. For that reason, they were widely used on amphibious ships, auxiliaries, and merchant ships.

Description

Probably the best automatic cannon anti-aircraft weapon of World War II, Bofors guns of this type remained in service long after the war ended. This weapon was used on almost every major USA and UK warship of World War II and was a very potent AA gun.

These guns are recoil operated and use a monobloc barrel with a detachable breech ring, breech casing and automatic loader. The barrel was attached to the breech ring via an interrupted screw design. The breech block was a vertical sliding type which was developed from the Finspong (Swedish arms manufacturer of the 1800s) 57mm Ssk M/89B. Although often listed as being 60 calibers long, all guns from all nations except Japan were actually 56.25 calibers in length.

Development by Bofors

This weapon traces its roots back to a 1918 Krupp design - the Bofors Company was partly owned by German interests until 1930 - but the finished product was entirely a Bofors design owing little or nothing to Krupp influence. During the late 1920s the Swedish Royal Navy approached Bofors a few times with requests to design a new 40 mm AA gun to replace the British 2-pdr. guns currently in service. Bofors showed little interest in this project as the size of any order from the Swedish Navy would be small and they did not see much possibility in foreign orders. However, the Navy persisted and finally offered to help fund the development costs. With this money in hand, Bofors started to actively work on a new AA weapon. The first Bofors test-bed prototype was finished late in the summer of 1930 and this fired three rounds using the automatic loader on 17 October 1930. Design and manufacturing of the first gun followed and single shots with it were fired on 10 November 1931. By 25 November 1931 trials had progressed to firing eight rounds in 7.58 seconds. This showed that the autoloader design concept would work, but more effort was needed before the prototype could meet the 130 rpm requirement. Official trials for the Swedish Navy took place successfully on 21 March 1932. This design was modified into a submarine gun and adopted by the Swedish Navy as the 40 mm L/43 Model 1932.

The basic design was further refined over the next two years, with 30,000 hours of drawing board work needed to produce 1,800 working drawings and 1,600 machine tool drawings that made up the improved 40 mm L/60 Model 1934. This model was exported to several countries but not adopted by the Swedish armed forces.

It was not until 1936 that the Swedish Army and Navy placed orders for a very slightly modified version and this became the 40 mm L/60 Model 1936 whose basic design was used for most guns produced during World War II by Bofors, the UK and the USA. Although the UK and USA halted production with the end of the war, Bofors continued to manufacture the 40 mm L/60 until 1954 when production was halted in order to concentrate on the more powerful 40 mm L/70 and 57 mm L/60 guns.

Origins

Back in 1918, German arms engineer Reinhold Becker came up with a 20x80mm round that fired using primer ignition blowback in a very large machine gun to fire at 300-rounds per minute. This gun was to be used to help sweep the sky of the Western Front of those pesky thousands of American, British, and French biplanes in the last year of World War 1. Too bad for Becker, (not to mention the Kaiser) the guns were never made in enough numbers to affect the war and his design was shelved.

In 1934 the Swiss based company of Oerlikon Contraves (Oerlikon being the name of the town the factory was located in and contra-aves being Latin for “against birds”) dusted off Becker’s design and super-sized it to be able to better shoot down the more modern fighters of the 1930s.

This gun, typically just referred to as the 20mm Oerlikon, became perhaps one of the most effective AAA (antiaircraft artillery) cannons of World War 2.

Design

Oerlikon Contraves took the design of the SEMAG; a larger version of Becker’s earlier gun chambered in 20x100RB and started a redesign. The final product used a simple blowback action, like the M1A1 Thompson and M3 Grease Gun to cycle. This required the use of a very heavy (to retard the recoil) open bolt without a locking lug as well as a huge spring (that weighed six pounds) that would push the bolt forward again after the round fired. This design cuts out gas impingement, piston rods, and even separate firing pins, creating a very simple action that is hard to break and what this meant was that the gun would run dirty, frozen, wet, unlubricated, full of blood, or encrusted with sea salt when others wouldn’t. Think of an all-steel 20mm Hi-Point Carbine that fired full auto from an open bolt and you have the basic design in mind.

In its final version, pitched in the late 1930s to the British and US Navies (as well as to the Germans and Japanese), the Oerlikon had been upgraded to the 20x110RB round at up to 450-rounds per minute. This huge 7-inch long, half-pound round used a 400-grain charge of IMR 4831 smokeless powder to propel a 2,000-grain projectile at 2,800 feet (850 meters) per second through a 55-inch long 9-groove barrel. For comparisons, this round is about three times as heavy as the .50 BMG round fired by the M2 heavy machine gun. Produced in no less than 11 different loadings it could reach out to one mile away.

These cannon were not what you could consider ‘portable’. Weighing in at nearly 150-pounds with rather serious recoil, the gun could not be carried by a light vehicle let alone a squad of soldiers. The main use was in mounting it to ships at sea for the purpose of stitching up surface targets like small boats and shooting down attacking aircraft. In a pinch, they could also be used to suppress fire ashore on the beaches if the ship was brought in close enough.

Use

The US Navy had just a few hundred of these guns on hand when the Japanese struck Pearl Harbor on December 7, 1941. Unlike many overseas made guns that used a belt, the US Navy’s model used a distinctive 60-round spring loaded drum magazine on the top of the gun. By distributing the plans and letting contracts go to numerous automobile manufacturers including Hudson and General Motors, more than 120,000 of the guns were made before the end of the war. Coupled with the MIT-designed electric Mark 14 electric gunsight that triangulated an aiming point on a rapidly approaching aircraft stabilized by two internal gyros, it was one of the most advanced weapons of its day.

The hardy 20mm Oerlikon was mounted on everything from tugboats and minesweepers to aircraft carriers. Usually manned by a five-man crew, it could be fired by a single sailor in a pinch—and often was. In post-war studies it was found that no less than one third of the Japanese aircraft shot down over the Pacific were down so by the German-invented, Swiss-perfected, US-built Oerlikon.

The gun was also well used by the British, Soviets, and numerous other nations during the war. The Japanese themselves even used the design (as the Type 99 auto-cannon), which led to something of a Twilight Zone scenario; while US Navy Oerlikon gunners were firing at Japanese A6M Zero fighter planes (that carried their own Oerlikons) Japanese Navy Oerlikon gunners were using their nearly identical gun to fire at US Navy planes.

The 1.1"/75 caliber gun was an American anti-aircraft weapon of World War II, used by the United States Navy. The name means that it had a bore diameter of 1.1 inches (28mm) and barrel length of 75 x 1.1 inches = 82.5 inches (2.1m), using the "caliber" nomenclature common to large artillery pieces. The gun was designed to replace the M2 Browning and four barrels were required to duplicate the rate of fire. The first shipboard installation in 1939 was quickly nicknamed the “Chicago Piano”, possibly because it was the size of a baby grand piano and looked a little like a baby grand without its lid. Although the reminiscences of the sailors who served with these guns all agree on the nickname, no one seems to know where it originated.

By 1941, these guns had been mounted on destroyers, cruisers, battleships, aircraft carriers, and some auxiliary ships. Nearly a thousand guns had been produced before production shifted to more reliable shipboard anti-aircraft machine guns in 1942. Quantities were minimal; one mount for a destroyer, two mounts for pre-1930s battleships, and four mounts for North Carolina–class and newer battleships. On at least some ships they were director-controlled.

The gun was very unpopular with its crews; it was said that due to its tendency to jam, the only way to fire one was to position a gunner's mate on his back underneath the mount, equipped with an assortment of wrenches and hammers to clear them. It was replaced by Oerlikon 20mm cannon or Bofors 40mm guns whenever possible, but served until the end of the war on some ships. A twin Bofors gun was about the same weight, and was a much more powerful gun. The air-cooled Oerlikon had similar effective range and rate of fire with considerably less weight. The Oerlikon could not sustain fire for as long as the water-cooled 1.1", but six Oerlikons could be installed for the weight of a single 1.1" quad mount.

Regardless of these problems, the 1.1-inch guns were a welcome addition to the Fleet’s antiaircraft defenses and played an important role in protecting U.S. carriers at the battles of the Coral Sea and Midway.

Source: Wikipedia