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-inch (152 mm) dual-purpose guns and with a heavy secondary armament. Although five ships of the class were planned in 1944, they were cancelled following the end of the war, before construction could begin.

Class overview
NameNeptune class
Operators Royal Navy
Preceded byMinotaur class (1943)
Succeeded by
Planned5
Cancelled5
General characteristics
Class and typeLight cruiser
Displacement18,700 long tons (19,000 t) deep load
Length662 ft (202 m) o/a
Beam76 ft (23 m)
Draught24 ft 9 in (7.54 m)
Installed power108,000 shp (81 MW)
Propulsion
Speed33 kn (61 km/h; 38 mph)
Range7,500 nmi (13,900 km; 8,600 mi) at 20 knots (37 km/h)
Complement1351
Armament
Armour
  • Belt 4–1.5 in (102–38 mm)
  • Bulkheads 4 in (100 mm)
  • Turrets 2–1 in (51–25 mm)

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 Minotaur class[lower-alpha 1] which were based on the pre-war Fiji class.[1] A small anti-aircraft (AA) cruiser design with six or eight 5.25 in (133 mm) dual-purpose guns (i.e. capable of both anti-ship and anti-aircraft fire) developed into the July 1943 N2 design N2, armed with four twin 5.25-inch turrets of a new design and displacing 8,650 long tons (8,790 t) standard, and this was approved for inclusion in the 1944 construction programme.[1][2][3] In October 1943, the First Lord of the Admiralty, Dudley Pound, resigned and his replacement, Andrew Cunningham, disliked the small cruiser and work was switched to a large cruiser, described at first as an "improved Belfast", armed with twelve 6-inch guns.[4]

Hull and machinery

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 ("large light cruiser") 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 preceding classes of cruiser, while the two superstructure blocks were longer than in previous ships; the forward superstructure extending back to the forward funnel and 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 ( 28 knots (52 km/h; 32 mph) in deep load condition) was inadequate to keep up 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); 32 knots (59 km/h; 37 mph) at full load.[5] The machinery was to be laid out in a 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. It was noted though by the Director of Naval Construction in June 1945 that the boiler rooms were still too close to avoid the possibility of both being 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]

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 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. 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 2] 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 130 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 4.5 inch (113 mm) Mark V dual purpose guns in 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 yd (18,000 m), with a maximum effective altitude for anti-aircraft fire of 19,700 ft (6,000 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. When the gun entered service, the power rammer proved unreliable and hand loading reduced the rate of fire to about 10–12 rounds per minute per barrel.[15][16] The 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 as seven twin Bofors and four twin Oerlikons around the bridge, three twin Bofors and eight twin Oerlikons around the aft superstructure and two 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; two Low-Angle (LA) directors for the 6-inch guns for use against surface targets, four barrage directors for the 6-inch guns for barrage fire against aerial targets, and 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]

Armour

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]

Complement

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

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 Bellerophon (originally ordered as a Minotaur-class cruiser), construction of which had been suspended after it was laid down, to the new design, giving a total of six ships.[lower-alpha 3] Completion by 1950 was expected.[7][3][17] The programme continued following the end of the war, with pressure growing to divert shipbuilding capacity to build more profitable ocean passenger liners, with it being hoped in November 1945 that two ships could be laid down as soon as possible.[20] In late February–March 1946 the Sea Lords, in drawing up the 1947 ship programme, decided to cancel the Neptune class. The order for Bellerophon was cancelled with the shipbuilder on 28 February 1946 and the Neptune class stopped in ADM 205/64 due to the lack of finance for cruiser construction in post war austerity Britain[21] and deep division among the naval staff over the role of the cruiser in AA defence and joint operation with aircraft carriers in defence of and attack on trade. Given the priority of air defence, further consideration and planning with the United States Navy was required to determine the desired size and calibre of long range AA guns, and particular study was ordered on the new US Worcester, Mitscher and Juneau classes.[lower-alpha 4] The attempts at a follow on Minotaur class, were only marginally smaller, failing to see the Royal Navy could not justify large cruisers post war and the box dimensions of a Tiger or N2 was the limit cost containable or justifiable in industrial or financial UK post-war reality. Work on development of the Mk 3 5.25-inch twin turret intended for the N2 class continued at Elswick to 1948.[23] A target of 48 rpm for AA and 24 rpm for surface engagement was aimed for. In 1948 it was decided to scale down the 5.25-inch to a 5-inch 62 calibre twin mounting. Five inch guns seemed a likely NATO standard with the US Navy developing 5-inch/54 calibre twin and single mounts. The decision later in 1948 against joint development, reflected British desire for independent naval capability and maintenance of its munitions exports. The American gun was really too advanced for much collaboration but the US single mount was in service by 1953 and with a rate of 27 rpm a decade later. Britain's ambitious plan for a 5-inch 62 calibre twin 60rpm mount, was beyond UK industry as was the 1951 lighter, single 5/62 calibre of 40rpm, medium range AA was beyond UK capability at the time for lightweight design, cost and machine tools for the cruiser destroyer which was finally abandoned in 1953 or even the final (Z- Zed) March 1955 conventional RN cruiser 85Z proposal of the future RN CNC, the enhanced 'Tiger/ N2 class' 8000 tons gun cruiser with 2 twin inch 5 inch, three twin 3/70, 4 STAAG Mk 2 and AD/AW 965 which the Admiralty board would have approved for the 1956 programme,[24] but was vetoed by the Chief Naval Gunnery due to failure of past 5-inch guns development and the fact that development of new guns was too expensive and could not compete with Seaslug missile development for resources.[25]


Notes
  1. later renamed Swiftsure class when HMS Minotaur was transferred to the Royal Canadian Navy and entered service as Ontario
  2. In British ordnance terminology, QF stands for Quick Firing, with the propellant change enclosed in a metal case rather than in bags
  3. Some sources also state that the partially built Minotaur-class cruiser Hawke, laid down in 1943, was also reordered as a Neptune.[5][19]
  4. The development of the Neptune-class design and its cancellation were covered by the Royal Navy, Director of Naval Construction Charles Lillicrap in a memo on 11 April 1946, ADM 167/127:1946.[22]

    Citations
    1. Friedman 2010, pp. 261–262
    2. Brown 2012, p. 85
    3. Brown & Moore 2012, p. 26
    4. Friedman 2010, p. 262
    5. Lenton 1973, p. 143
    6. Brown & Moore 2012, p. 84
    7. Gardiner & Chesneau 1980, p. 36
    8. Brown & Moore 2012, p. 27
    9. Friedman 2010, p. 261
    10. Friedman 2010, pp. 264, 266
    11. Friedman 2010, pp. 264, 371–372
    12. Friedman 2010, pp. 371–372
    13. DiGiulian, Tony (2 September 2016). "6"/50 (15.2 cm) QF Mark N5". NavWeaps.com. Retrieved 10 February 2017.
    14. Lenton 1973, p. 142
    15. Friedman 1997, p. 458
    16. DiGiulian, Tony (1 December 2015). "4.5"/45 (11.4 cm) QF Mark V: (Mark 6 and Mark 7)". NavWeaps.com. Retrieved 11 February 2017.
    17. Friedman 2010, p. 266
    18. Lenton 1973, pp. 142–143
    19. Roberts & Raven 1980
    20. Friedman 2010, pp. 266–267
    21. Brown & Moore 2012, p. 26.
    22. Brown & Moore 2012, p. 26-28.
    23. Moore. Cruisers 1946-56 in Warship 2006
    24. Moore. Warship 2006
    25. Moore (2006) p55

    Sources
    • Brown, David K. (2012). Nelson to Vanguard: Warship Design and Development 1923–1945. Barnsley, UK: Seaforth Publishing. ISBN 978-1-84832-149-6.
    • Brown, David K.; Moore, George (2012). Rebuilding the Royal Navy: Warship Design Since 1945. Barnsley, UK: Seaforth Publishing. ISBN 978-1-84832-150-2.
    • Friedman, Norman (2010). British Cruisers: Two World Wars and After. Barnsley, UK: Seaforth Publishing. ISBN 978-1-84832-078-9.
    • Friedman, Norman (1997). The Naval Institute Guide to World Naval Weapons Systems 1997–1998. Annapolis, Maryland, USA: Naval Institute Press. ISBN 1-55750-268-4.
    • Gardiner, Robert; Chesneau, Roger, eds. (1980). Conway's All The World's Fighting Ships 1922–1946. London: Conway's Maritime Press. ISBN 0-85177-146-7.
    • Gardiner, Robert; Chumbley, Stephen, eds. (1995). Conway's All The World's Fighting Ships 1947–1995. Annapolis, Maryland, USA: Naval Institute Press. ISBN 1-55750-132-7.
    • Lenton, H.T. (1973). Navies of the Second World War: British Cruisers. London: Macdonald & Co. ISBN 0-356-04138-7.
    • Roberts, John & Raven, Alan (1980). British Cruisers of World War Two. Arms & Armour Press. ISBN 0853683042.
    • Moore (2006), "Cruiser Development 1946-56", Warship 2006, Conway Maritime Press, ISBN 9781844860302


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