QF 6 inch Mark N5 gun

Ordnance QF 6 inch Gun Mark N5
HMS Tiger at sea in 1965, showing the large twin 6 inch gun mounting
Type	Naval gun
Place of origin	United Kingdom
Service history
In service	1959-1979
Used by	Royal Navy
Production history
Designed	1944 (suspended and resumed, 1948)
Specifications
Weight	15,344 lbs. (6,960 kg)
Length	315 in (8.001 m)
Barrel length	300 in (7.62 m) (50 calibres)
Shell	AP: 129.75 lb (58.85 kg) HE: 132 lb (60 kg)
Calibre	6-inch (152.4 mm)
Breech	Horizontally sliding breech block (hydraulic operation)
Carriage	Modified Mark XXVI (Mark 26)
Elevation	-5 to +78.5 degrees
Rate of fire	15 to 20 rounds per minute
Muzzle velocity	2,520 feet per second (768 m/s)
Maximum firing range	25,000 yd (23,000 m) at 45 degrees elevation (firing AP shot)

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.

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.