Neptune-class cruiser

The Neptune-class was a proposed class of cruisers planned for the British Royal Navy in the latter years of the Second World War. They were large ships which were to be armed with twelve 6 in (152 mm) Dual Purpose guns and with a heavy secondary armament. While five ships of the class were planned in 1944, they were cancelled following the end of the war, before construction could begin.

Development and design
In 1942, work began at the British Admiralty as to the requirements for the next class of cruisers to be built for the Royal Navy as a follow-on to the and s, which were both based on the pre-war. At first the favoured design was a small anti-aircraft cruiser armed with six or eight 5.25 in (133 mm) dual-purpose (i.e. capable of both anti-ship and anti-aircraft fire) and in 1943, design N2, armed with four twin 5.25 inch turrets of a new design and displacing 8650 LT standard, was approved for inclusion in the 1944 construction programme. In October 1943, the First Lord of the Admiralty, Dudley Pound, resigned and his replacement, Andrew Cunningham disliked the small cruiser, preferring 6 inch gun armed ships, and instead work was switched to a large cruiser, described at first as an "improved HMS Belfast (C35)", armed with twelve 6 inch guns.

Hull and machinery
The new design was 662 ft long overall and 655 ft at the waterline, with a beam of 76 ft and a draught of 24 ft. Displacement was 15350 LT standard and 18700 LT deep load. The ships were not fitted with facilities for carrying aircraft, so the bridge was lower than in predecessing classes of cruiser, while the two superstructures 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. A long forecastle was planned, reaching back beyond the aft funnel, although in 1946, it was suggested to change to a flush-deck hull.

One of the problems identified with the small 5.25 inch-armed cruiser was that its speed of 28 kn in deep load condition was inadequate to keep pace with the aircraft carriers that the cruisers were meant to escort. The new design therefore had a much higher design speed. Four Admiralty 3-drum boilers fed steam at 400 psi to Parsons single-reduction geared steam turbines rated at 108000 shp and driving four propeller shafts. This gave a design speed of 33 kn or 32 kn at full load. 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. The ship was planned to have a range of 7500 nmi at 20 kn.

Armament
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. The new turret, the Mark 25, mounted three QF 6 inch Mark V guns, capable of firing at a rate of 10–12 rounds per minute per gun compared with 5–6 for the Mark 24, and elevating to 80 degrees, giving an anti-aircraft capability. A 129.75 lb armour-piecing shell could be fired to a range of 25000 yd. The turrets were arranged conventionally on the ships' centreline, with two forward and two aft.

Secondary armament consisted of six QF Mark 6 4.5 in (113 mm) dual purpose twin turrets as used in the. These could fire a 55 lb shell to a range of 20000 yd, with a maximum effective altitude for anti-aircraft fire of 19700 ft. 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 servie, the power rammer proved unreliable, with hand loading reducing rate of fire to about 10–12 rounds per minute per barrel. 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. Four quadruple 21 inch (533 mm) torpedo tubes were fitted.

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 six 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).

Armour
The ships' main vertical belt armour was 4 in thick amidships, which thinned to 1+1/2 in forwards and aft. Horizontal armour consisted of a 1 in thick upper deck and a 1 inch thick lower deck, thickening to $1 1/2$ inch over the ships' steering gear. The main gun turrets had 4 inch-thick faces with 2 in thick armour on the turret roof, sides and rear. Longitudinal and transverse armoured bulkheads of up to 4 inch thickness were placed around the ships' machinery compartments and magazines.

Complement
The ships had a planned complement of 1351 officers and men when operating as a flagship.

Construction programme
Five ships of the new design, which was now known as the Neptune-class, to be named Neptune, Centurion, Edgar, Mars and Minotaur, were included in the 1944 construction programme. In addition, it was planned to complete the Tiger-class cruiser Bellepheron, construction of which had been suspended before it was laid down, to the new design, giving a total of six ships. Completion by 1950 was expected. The programme continued following the end of the war, despite pressures to divert shipbuilding capacity to built merchant ships, with it being hoped in November 1945 that two ships could be laid down as soon as possible. In 1946, however, work on the Neptune-class was stopped as the class was thought to be out of date and too large.

To meet the Royal Navy's continuing requirements for new cruisers, a new design was proposed, the Minotaur-class, to be armed with five twin 6 inch dual purpose turrets and up to eight twin 3 inch anti-aircraft guns. 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, 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. By 1947, it was decided that no cruisers would be built for the next five years owing to financial constraints, with design work on the Minotaur-class petering out in the early 1950s. The new 6 and 3 inch mounts were eventually used when three Tiger-class cruisers were completed to a new design in the late 1950s.