QF 6-inch Mark N5 gun
The QF 6-inch Gun Mark N5 (initially designated QF 6-inch Mk V) was a British naval gun, which was developed in the post-war period. It was the last large gun to be operational with the Royal Navy. Development. The development of the Mark V gun started during the Second World War and was intended for triple Mark 25 mountings on the projected "Neptune"-class cruisers. When the Neptune-class ships were cancelled in 1946, the gun was redesigned to be mounted in pairs to the new and complex Mark 26 dual purpose  mounting and gun turret designed for rapid automatic fire on the projected "Minotaur"-class cruiser. These were to be the first British 6-inch guns in over sixty years to use brass cartridges instead of bagged charges. By the time the first two experimental weapons had been completed in 1949, the "Minotaur"-class had also been cancelled, and after some time it was decided to use the N5 gun (as the Mark V had been redesignated) and the Mark 26 mounting, on the "Tiger"-class cruisers, whose hulls had been built during the war and had since been totally redesigned. Initial trials were  undertaken at the Shoeburyness ranges on the Essex coast. A prototype of the complete gun, mounting and turret system was mounted on the former heavy cruiser, HMS "Cumberland", which had been converted to a trials ship in 1949–1951. The turret was mounted in the "B" (forward, upper) position, while mounted on the "X" position (aft, upper) was a twin Vickers Ordnance QF 3in Mark N1 gun which was also under development for the "Tiger"-class. In April 1957, "Cumberland" sailed for the Mediterranean for firing trials, during which she expended 645 6-inch rounds. The guns were operated in conjunction  with the Gun Direction System (GDS1) and a Type 992 radar. The cruisers were to carry two twin 6-inch mounts, fore and aft, and together with the ships' 3-inch guns, was intended to be able to fire a barrage of 800 shells per minute. Service. The guns entered service with the Royal Navy when HMS "Tiger" was commissioned in 1959. The weapon system gained a reputation for unreliability and difficult maintenance, however the main problem was the number of technicians required to keep the guns operational. This was especially true of the earlier hydraulically actuated mountings, later versions  were electrically operated. Two of the ships, "HMS" Blake in 1969 and HMS "Tiger" in 1972, underwent a radical conversion which replaced the aft 6-inch turret with a helicopter flight deck and hangar. These two ships remained in service until December 1979 when "Blake" fired her guns for the last time in the English Channel; they were the last 6-inch guns ever to be fired from a British warship.