During the early 1930s the Royal Navy
Perhaps less evident were questions of power selected two weapons to fulfil the short-range AA requirements. Powered mountings offered much roles: the .5" Vickers Mk III heavy machine gun and faster training and elevation rates but were more the 2pdr which has already been mentioned. Both expensive and vulnerable to loss of power through guns were belt-fed and water-cooled.
The .5" was originally intended for all three services, but only the RN made extensive use of it. The gun used Vickers's own 12.7 X 81 cartridge and fired at a rate of about 700 rpm. The first naval application appeared in the early 1930s in a four-barrel mounting (most unusually, with the barrels vertically stacked) which weighed between 1,000kg and 1,300kg and was intended mainly for destroyers. Subsequently, twin- and single-barrelled versions were produced for smaller craft. All of these were unpowered except for the hydraulic Mk V twin, which had respectable training and elevation rates of 72 and 50 degrees per second respectively. This weighed about 500kg and was typically fitted to fast patrol boats.
The 2pdr gun weighed between 356kg and 416kg. Ammunition was in disintegrating steel-link belts which could be joined to provide up to 140 rounds per gun. Initially, muzzle velocity achieved by the 40 X 158R cartridge was only 620 m/s and the rate of fire some 90 rpm. The 2pdr was designed to be fitted in two mountings: an eight-barrel mounting weighing around 16,000kg which was intended to arm battleships and aircraft carriers (first fitted to HM ships War spite, Rodney and Nelson in the late 1930s), and a four-barrel version which first emerged on County class cruisers and Tribal class destroyers. In contrast to the .5", the
.5" Vickers quad naval mounting barrels were arranged in two side-by-side pairs, one
2pdr Vickers quad naval mounting (Leo Marriott)
and weighed 8,700kg; later, powered marks weighed between 10,000kg and 11,000kg. Single barrel mountings weighing 1,400-1,800kg appeared later and were used in a wide variety of vessels including fast patrol boats.
The size and weight of the four- and eight-barrel mountings is emphasised by comparison with typical medium-calibre equipment. A single 4" Mk XX weighed 10,000kg, a twin 4" Mk XIX 000kg, and a single 4.7" destroyer (low-angle) mounting some
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