Kent-class cruiser

Australia in 1937
Class overview
Name:	County class
Operators:	Royal Navy  Royal Australian Navy
Preceded by:	Hawkins class
Succeeded by:	York class
Subclasses:	Kent, London, Norfolk
In commission:	1928–1959
Planned:	15
Completed:	13
Cancelled:	2
Lost:	3
Retired:	10
General characteristics Kent class
Type:	Heavy cruiser
Displacement:	10,400 tons average standard 14,150 tons average full load
Length:	590 ft (180 m) p/p 630 ft (190 m) (o/a)
Beam:	68 ft (21 m) across bulges
Draught:	17.25 ft (5.26 m) standard 21.5 ft (6.6 m) full load
Propulsion:	8 × Admiralty three-drum boilers, Parsons (Brown-Curtis in Berwick) geared steam turbines on 4 shafts, 80,000 shp (60,000 kW)
Speed:	31.5 knots (58.3 km/h; 36.2 mph)
Range:	8,000 nautical miles (15,000 km; 9,200 mi) at 10 knots (19 km/h; 12 mph) 2,300 nautical miles (4,300 km; 2,600 mi) at 30 knots (56 km/h; 35 mph)
Complement:	685 standard, 710 as flagship, 784 during wartime
Armament:	8 × BL 8-inch (203 mm L/50) Mk.VIII guns in twin mounts Mk.I 4 × QF 4-inch (102 mm) L/45 Mk.V guns in single mounts HA Mk.III 8 × QF 2-pounder (40 mm) L/39 Mk.VIII guns in quad mounts HA Mk.VII (from 1925–) except Berwick; 16 in oct mounts Mk.VIII 8 × 0.5-inch (12.7 mm L/50) Mk.III machine guns in quad mounts Mk.I (from 1924–) 8 × 21-inch (533 mm) torpedoes in quad mounts (removed from 1935–)
Armour:	Main belt: 4.5-inch (110 mm) with 1-inch (25 mm) closing bulkheads (Berwick, Cumberland, Suffolk, Kent & Cornwall only, from 1935–) Lower deck: 1.25-inch (32 mm) over machinery 1.5-inch (38 mm) over steering gear Main box citadels: 1–4-inch (25–102 mm) sides 1-to-2.5-inch (25 to 64 mm) crowns Turrets: 1-inch (25 mm) faces, sides, rears, crowns & barbettes
General characteristics London class
Displacement:	9,840 tons standard average 13,315 tons full load
Length:	595 ft (181 m) p/p 632 ft 9 in (192.86 m) o/a
Beam:	66 ft (20 m)
Draught:	17 ft (5.2 m) standard 21 ft 6 in (6.55 m)
Speed:	32.25 knots (59.73 km/h; 37.11 mph)
Complement:	700 standard, 852 during war
Armament:	8 × BL 8-inch (203 mm) L/50 Mk.VIII guns in twin mounts Mk.I* 4–8 × QF 4-inch (102 mm) L/45 Mk.V guns in single mounts HA Mk.III 4 × QF 2-pounder (40 mm) L/39 Mk.II guns in single mounts HA Mk.I 8 × 0.5-inch (12.7 mm) L/50 Mk.III machine guns in quad mounts Mk.I 8 × 21-inch (533 mm) torpedoes in quad mounts
Armour:	Main belt: 3.5-inch (89 mm) with 1-inch (25 mm) closing bulkheads (London only, from 1938–)
Notes:	Other characteristics as per Kent
General characteristics Norfolk class
Displacement:	10,400 tons standard 13,775 tons full load
Length:	595 ft 1 in (181.38 m) p/p 632 ft 9 in (192.86 m) o/a
Beam:	66 ft (20 m)
Draught:	18 ft (5.5 m) standard 21 ft 6 in (6.55 m)
Complement:	710 standard, 819 during war
Armament:	8 × BL 8-inch (203 mm L/50) Mk.VIII guns in twin mounts Mk.II 8 × QF 4-inch (102 mm L/45) Mk.XVI guns in twin mounts HA/LA Mk.XIX (from 1937–) 16 × QF 2-pounder (40 mm L/39) Mk.VIII guns in oct mounts HA Mk.VIII
Notes:	Other characteristics as per London

The County class was a class of heavy cruisers built for the Royal Navy in the years between the First and Second World Wars. They were the first post-war cruiser construction for the Royal Navy and were designed within the limits of the Washington Naval Treaty of 1922. Such ships, with a limit of 10,000 tons, standard displacement and 8-inch calibre main guns may be referred to as "treaty cruisers" (the term "heavy cruiser" was not defined until the London Naval Treaty of 1930).

The thirteen Counties were built in three distinct sub-classes: the Kent, London and Norfolk classes. They were the only 10,000-ton 8-inch gun, or "A", cruisers that the Royal Navy built. The Counties are remembered for their distinctive three-funnel layout and service in all the major naval theatres of the Second World War.

In an attempt to extract more ships from the treaty limits, the navy planned to construct 8,250-ton "B" ships, six of which could be built in place of five Counties. The extra ship that this afforded was an attractive proposition for a navy that had the immense peacetime commitments of empire. In the event, peacetime economies and politics intervened and only two B-type cruisers were built, an 8-inch gun modified County design: the York class.

In 1929, the mean cost of each "A" ship was estimated to be £2,180,000 whilst the mean cost of each "B" ship was estimated to be £1,800,000.

The 10,000 ton treaty cruisers were the first type of warships built to internationally agreed restrictions. These restrictions posed new engineering challenges and forced compromises upon designers in how to extract the best balance of speed, armament and protection. The United States Navy adopted a design with triple-gun turrets, allowing the hull to be shortened thus saving weight that could be put into protection. This approach however was at the expense of requiring increased installed power, as the speed of a ship is a function of the ratio of length to beam. The Royal Navy had a requirement for a vessel for colonial trade route defence, which required a good cruising range and speed and independent fighting power. This determined the need for a long hull and the use of four twin-gun turrets, with any remaining displacement invested in protection.

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