Neptune-class cruiser

The new design was 662 feet (201.8 m) long overall and 655 feet (199.6 m) at the waterline, with a beam of 76 feet (23.2 m) and a draught of 24 feet 9 inches (7.5 m),[5] with the ships' hull form based on that of the Courageous-class battlecruiser of the First World War.[6] Displacement was 15,350 long tons (15,596 t) standard and 18,700 long tons (19,000 t) deep load.[7] The ships were not fitted with facilities for carrying aircraft, so the bridge was lower than in predecessing classes of cruiser, while the two superstructure blocks were longer than in previous ships, with the forward superstructure extending back to the forward funnel and while the aft superstructure covered the base of the aft funnel.[5] A long forecastle was planned, reaching back beyond the aft funnel,[8] although in 1946, it was suggested to change to a flush-deck hull.[3]

One of the problems identified with the small 5.25-inch-armed cruiser was that its speed of 28 knots (52 km/h; 32 mph) in deep load condition was inadequate to keep pace with the aircraft carriers that the cruisers were meant to escort.[2][9] The new design therefore had a much higher design speed. Four Admiralty 3-drum boilers fed steam at 400 pounds per square inch (2,800 kPa) to Parsons single-reduction geared steam turbines rated at 108,000 shaft horsepower (81,000 kW) and driving four propeller shafts. This gave a design speed of 33 knots (61 km/h; 38 mph) or 32 knots (59 km/h; 37 mph) at full load.[5] The machinery was to be laid out to the unit scheme, with two sets of boilers and turbines separated to reduce the potential for a single torpedo or shell hit to cause complete loss of power, although it was noted by the Director of Naval Construction in June 1945 that the boiler rooms were still too close to avoid the potential for both to be knocked out by a single hit.[10] The ship was planned to have a range of 7,500 nautical miles (13,890 km; 8,631 mi) at 20 knots (37 km/h; 23 mph).[5]

The main gun armament was to be twelve 6-inch (152 mm) guns in four triple turrets. Consideration was given at first to using the existing Mark 24 mountings, as planned for the Tiger-class ships, as these could be delivered relatively quickly. The Mark 24, which was an improved version of the pre-war turret, was considered old fashioned however, and a new mounting was chosen accepting the delays in construction that would ensue.[11] The new turret, the Mark 25, mounted three QF 6 inch Mark V guns,[lower-alpha 1] capable of firing at a rate of 10–12 rounds per minute per gun compared with 6-8 for the Mark 24, and elevating to 80 degrees, giving an anti-aircraft capability.[7][12] A 129.75 lb (59 kg) armour-piecing shell could be fired to a range of 25,000 yards (22,860 m).[13] The turrets were arranged conventionally on the ships' centreline, with two forward and two aft.[14]

Secondary armament consisted of six QF Mark 6 4.5 in (113 mm) dual purpose twin turrets as used in the Daring-class destroyer.[14] These could fire a 55 lb (25 kg) shell to a range of 20,000 yards (18,288 m), with a maximum effective altitude for anti-aircraft fire of 19,700 feet (6,005 m).[15] The guns were semi-automatic and fitted with a power loader, giving a maximum rate of fire of 24 rounds per minute per barrel, although when the gun entered service, the power rammer proved unreliable, with hand loading reducing rate of fire to about 10–12 rounds per minute per barrel.[15][16] Close-in anti-aircraft armament consisted of 20 Bofors 40 mm guns in 10 "Buster" self-contained twin mounts and 28 Oerlikon 20 mm cannon in 14 twin mounts. This was arranged with 7 twin Bofors and 4 twin Oerlikons around the bridge, 3 twin Bofors and 8 twin Oerlikons around the aft superstructure and 2 twin Oerlikons at the stern of the ship.[14][17] Four quadruple 21 inch (533 mm) torpedo tubes were fitted.[14][7]

Comprehensive fire-control equipment was proposed, with two Low-Angle (LA) directors for the 6-inch guns for use against surface targets, together with four barrage directors for the 6-inch guns for barrage fire against aerial targets, with three combined HA/LA directors for the 4.5-inch guns for use against both surface and air targets. Each Bofors mount was to be fitted with an integrated fire control radar. This gave a capability for up to 17 aerial targets to be engaged simultaneously (four with long-range barrage fire from the 6-inch guns, three by the 4.5-inch guns and ten at short-range by the Bofors guns).[18]

The ships' main vertical belt armour was 4 inches (100 mm) thick amidships, which thinned to 1 ¹⁄₂ inches (38 mm) forwards and aft. Horizontal armour consisted of a 1-inch (25 mm) thick upper deck and a 1-inch thick lower deck, thickening to ​1 ¹⁄₂ inches over the ships' steering gear. The main gun turrets had 4-inch-thick faces with 2-inch (51 mm) thick armour on the turret roof, sides and rear.[5] Longitudinal and transverse armoured bulkheads of up to 4-inch thickness were placed around the ships' machinery compartments and magazines.[7]

The ships had a planned complement of 1,351 officers and ratings when operating as a flagship.[5][17]

To meet the Royal Navy's continuing requirements for new cruisers, a new design was proposed called Design Z, or the 1947 Minotaur class, to be armed with five twin 6-inch dual purpose turrets and up to eight twin 3-inch anti-aircraft guns.[26] The twin 6-inch turret, the Mark 26, was of a new design and had a rate of fire of 20 rounds per minute per gun,[27][28] while the twin 3-inch guns had a very high rate of fire and replaced both the 4.5 inch and 40 mm and 20 mm close-in batteries.[26] In 1947, it was decided that no cruisers would be built for the next five years owing to financial constraints,[27] although the requirement for cruisers remained. The design to meet these requirements was not finalised, with extensive development work expected to be required for the all-new ship's armament.[lower-alpha 3][30] Design work on the Minotaur class petered out in the early 1950s.[31]

After design work in the late 1940s aimed at producing a "1960 cruiser" came to nothing,[32][33] efforts switched to a smaller design, the "Cruiser/Destroyer", to be armed with three rapid-fire 5-inch (127 mm) guns, which was abandoned in 1953.[34] Effort then switched to guided-missile cruisers, which by July 1955 had settled on a 15,400 long tons (15,600 t) ship armed with a two twin Mark 26 6-inch turrets, two 3-inch turrets and a single Seaslug anti-aircraft missile launcher, the design was the same length as the 1951 Minotaur cruiser but with 3 ft more beam, but was limited to one Seaslug channel by a 16,000-ton size constraint and the RN decided that 984 3D radar and two 901 control channels were required for 48 conventional Seaslugs and 16 nuclear AA Seaslugs, along with a gun armament of two Mk 26 twin 6-inch guns forward and 4 twin 3-inch/70 guns. This the last RN cruiser design, 96A GWA, an 18,200 design which Mountbatten rejected on 4 January 1957, was a design somewhat influenced by USS Galveston, the Talos cruiser, with a full gun armament forward, finally commissioned in 1958 and USS Northampton, a command cruiser in its 1957, fit out of four 5-inch/54 calibre and 4 twin 3-inch/70 calibre guns which reflected the volume demanded by the magazines of the new auto guns and aW/AD radars. The three GW missile cruisers, enhanced Minotaurs in a sense, were included in the 1956 construction programme for the Royal Navy, with delivery from 1962, but they were cancelled by Chief of Naval Staff (CNS) Admiral Mountbatten and Admiral Peter Gretton after the Suez Crisis and the following UK financial crisis and revelation the Soviet Navy had abandoned its Sverdlov-class cruiser construction line under new Premier Nikita Khrushchev . Mountbatten, who became the new CNS in 1957 ordered a review of the cruiser programme immediately on 4 January 1957, believing the large cruisers were of no practical use and far too big as Seaslug GMS ship. On 16 January 1957 the cruiser design office was closed and the three 18,000-ton cruisers that had been ordered were cancelled in April 1957, along with the conversion of HMS Superb as a fourth Tiger.[35] The new 6- and some 3-inch mounts were eventually used when three Tiger-class cruisers were completed to a new design in the late 1950s,[36] while the County-class destroyers met the Royal Navy's requirements for a surface-to-air missile armed ship.[37] Most of the new 3-inch/70 calibre mounts were however sold off to Canada.