3-inch 20 cwt
The 3-inch 20 cwt is an anti-aircraft gun developed by the British in 1914. "3-inch" refers the the shell caliber used and "20 cwt" indicates the gun's weight. It is a common weapon on naval warships and submarines and also saw use on land on trailers.
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History of creation and combat usage
The gun was based on the Vickers 3-inch naval gun with the addition of modifications asked for by War Office. The gun was delivered in 1914 and had a semi-automatic vertical sliding breech-block for quick-firing operations. However, this functioning was removed due to difficulties in firing at higher elevation angles with that function, which reduced the firing rate from 22 rounds per minute to 20 rpm, though the effective rate of fire was 16 to 18 rounds per minute.
During the inter-war year between World War I and World War II, the 3-inch gun saw improvements in barrels and land trailers. It stayed in service in the British Army, Navy, and Home Guard until it was succeded by the 3.7 inch anti-aircraft gun in 1938.
The 3-inch gun was pressed into service in World War I as an anti-aircraft gun when it was realized that the British had no capable anti-aircraft artillery available. These guns were installed in key locations in Britain and were used by the Royal Naval Volunteer Reserves. The 3-inch 20 cwt proved to be the only adequate anti-aircraft gun to target high altitude targets such as Zeppelins and bombers. By 1916, the majority of the anti-aircraft defense in Britain was the 3-inch 20 cwt gun, comprising of 2/3 or the total air defense guns installed.
In World War II, Britain had a total of 500 of these guns available for use and were used in the same role as the last war. The guns stayed in service until the 3.7 inch AA gun came into service in 1938, but the high number of 3-inch 20 cwt guns available meant they stayed in service for much longer until the 3.7 inch became more prevalent. In 1941, some 100 of these guns were converted into anti-tank guns known as 3-inch 16 cwt anti-tank gun, but these did not see service outside the Home Guard. An attempt to fit the gun onto a mobile platform was done with the Churchill tank in a fixed superstructure construction to create the 3 inch Gun Carrier. The vehicle was ready in early 1942, but the production of the more capable 17-pounder led to a decline in interest in this project.