BL 6 inch Mk XXIII naval gun

Ordnance BL 6 inch gun Mk XXIII
Forward triple-gun turrets of HMS Belfast, March 2005
Type	Naval gun
Place of origin	United Kingdom
Service history
In service	1931 - 1985
Used by	Royal Navy Royal Australian Navy Royal New Zealand Navy Royal Canadian Navy Indian Navy Peruvian Navy Republic of China Navy People's Liberation Army Navy
Wars	Second World War Korean War
Production history
Number built	469^[1]
Specifications
Weight	7 tonnes^[1]
Barrel length	300 inches (7.6 meters)^[1]

Shell	112 pounds (51 kg)
Calibre	6-inch (152.4 mm)^[1]
Muzzle velocity	2760 feet per second (840 m/s)^[1]
Maximum firing range	25,480 yd (23,300 m) at 45 degrees elevation^[1]

The 50 calibre BL 6 inch gun Mark XXIII^{[note 1]} was the main battery gun used on the Royal Navy and British Commonwealth's conventional (non-anti-aircraft) light cruisers built from 1930 through the Second World War, and passed into service with several other navies when ships were disposed of after the end of the War.

Description

Handling cordite charges inside a Mk XXIII turret aboard HMS Jamaica, 1943

Breech with shell on loading tray of centre gun in a turret on HMS Belfast, 2006

It replaced the BL 8 inch Mk VIII naval gun used on earlier Washington Naval Treaty cruisers. These built-up guns consisted of a tube and 4.5 metre jacket with a hand-operated Welin breech block. Cloth bags contained 14 kg (30 pound) charges of cordite or flashless (NQFP) powder for a 51-kg (112-pound) projectile. Useful life expectancy was 1100 effective full charges (EFC) with standard cordite and 2200 EFC with NQFP per barrel.^[1] The typical maximum rate of fire was eight rounds per gun, per minute.^[2] The Mk XXIII turret design was improved through a "long trunk" ammunition hoist, which reduced the crew requirements and increased the speed of the ammunition hoists. As in the MK XXII turret loading could be accomplished at any angle up to 12.5 degrees gun elevation.^[3] A RN gunnery officer on HMS Bermuda gave details of the loading cycle which could be attained in the Mk XXIII turret with a well trained crew: "...a loading cycle of four and a half to 5 seconds was attained at low elevation, another two to three seconds being required with the guns elevated for long range. The time would lengthen as fatigue set in, but was creditable..." ^[4]

Ships mounting BL 6 inch Mk XXIII guns

Ship	Gun Installation^[1]
HMNZS Achilles	four 95-ton Mk XXI twin turrets
HMS Ajax	four 95-ton Mk XXI twin turrets
HMS Arethusa	three 95-ton Mk XXI twin turrets
HMS Aurora	three 95-ton Mk XXI twin turrets
HMS Belfast	four 175-ton Mk XXIII triple turrets
HMS Bermuda	four 175-ton Mk XXIII triple turrets
HMS Birmingham	four 150-ton Mk XXII triple turrets
HMS Ceylon	three 175-ton Mk XXIII triple turrets
HMS Edinburgh	four 175-ton Mk XXIII triple turrets
HMS Fiji	four 175-ton Mk XXIII triple turrets
HMS Galatea	three 95-ton Mk XXI twin turrets
HMS Gambia	four 175-ton Mk XXIII triple turrets
HMS Glasgow	four 150-ton Mk XXII triple turrets
HMS Gloucester	four 150-ton Mk XXII triple turrets
HMAS Hobart	four 95-ton Mk XXI twin turrets
HMS Jamaica	four 175-ton Mk XXIII triple turrets
HMS Kenya	four 175-ton Mk XXIII triple turrets
HMNZS Leander	four 95-ton Mk XXI twin turrets
HMS Liverpool	four 150-ton Mk XXII triple turrets
HMS Manchester	four 150-ton Mk XXII triple turrets
HMS Mauritius	four 175-ton Mk XXIII triple turrets
HMS Neptune	four 95-ton Mk XXI twin turrets
HMS Newcastle	four 150-ton Mk XXII triple turrets
HMS Newfoundland	three 175-ton Mk XXIII triple turrets
HMS Nigeria	four 175-ton Mk XXIII triple turrets
HMCS Ontario	three 175-ton Mk XXIII triple turrets
HMS Orion	four 95-ton Mk XXI twin turrets
HMS Penelope	three 95-ton Mk XXI twin turrets
HMAS Perth	four 95-ton Mk XXI twin turrets
HMS Sheffield	four 150-ton Mk XXII triple turrets
HMS Southampton	four 150-ton Mk XXII triple turrets
HMS Superb	three 175-ton Mk XXIII triple turrets
HMS Swiftsure	three 175-ton Mk XXIII triple turrets
HMAS Sydney	four 95-ton Mk XXI twin turrets
HMS Uganda	three 175-ton Mk XXIII triple turrets

Shell trajectory

Range^[1]	Elevation	Time of flight	Descent	Impact velocity
5000 yd (4.6 km)	2° 23′	7 sec	3° 0′	1939 ft/s (591 m/s)
10000 yd (9.1 km)	6° 15′	16 sec	9° 57′	1371 ft/s (418 m/s)
15000 yd (14 km)	13° 6′	29 sec	23° 38′	1098 ft/s (335 m/s)
20000 yd (18 km)	24° 7′	47 sec	39° 52′	1087 ft/s (331 m/s)
24500 yd (22.4 km)	41° 4′	71 sec	56° 27′	1159 ft/s (353 m/s)

Ammunition

S.A.P. shells (left), cordite cartridge (lower right) and cartridge container (centre right) on HMS Belfast

Surviving examples

Y turret from HMNZS Achilles (70), later INS Delhi (1948), is preserved at the entrance to Devonport Naval Base, Auckland, New Zealand.
A second turret from INS Delhi (1948), is preserved at the Indian Military Academy, Dehradun.
12 guns and four turrets are preserved on the museum ship HMS Belfast (C35) in London, UK
A number of Mark XXIIIs can also be found at English Heritage or other sites historical sites being used to represent earlier marks which were used as coastal artillery. Tilbury Fort, Essex, has one barrel; Coalhouse Fort, East Tilbury, Essex has two barrels; Gravesend, Kent, has one barrel; the Tynemouth gun emplacement has one barrel.

Notes

↑ Mark XXIII = Mark 23. Britain used Roman numerals to denote Marks (models) of ordnance until after World War II. Mark XXIII indicates this was the twenty-third model of BL 6-inch gun.

References

1 2 3 4 5 6 7 8 9 Campbell 1985 pp.34-36
↑ O.U. 6359A, Handbook for 6-Inch, B.L., Mark XXIII Guns on Triple, Mark XXII Mounting, 1937, page 8.
↑ Campbell, Naval Weapons of WWII, p.35-36.
↑ Brooke, p.200

Bibliography

Brooke,Geoffrey (1982). Alarm Starboard!. Cambridge: Stevens. ISBN 0850595789.
Campbell, John (1985). Naval Weapons of World War Two. Naval Institute Press. ISBN 0-87021-459-4.
Lenton, H.T. & Colledge, J.J (1968). British and Dominion Warships of World War Two. Doubleday and Company.

External links

Wikimedia Commons has media related to BL 6 inch Mk XXIII naval gun.

Tony DiGiulian, Britain 6"/50 (15.2 cm) BL Mark XXIII

British Commonwealth naval weapons of the Second World War

Monitor guns	BL 15 inch

Capital ship main armament	BL 14 inch BL 15 inch BL 16 inch

Heavy cruiser main armament	BL 7.5 inch Mk VI BL 8 inch Mk VIII

Secondary armament and light cruiser main armament	QF 4 inch Mk V QF 4.5 inch QF 5.25 inch BL 6 inch Mk XII BL 6 inch Mk XXII BL 6 inch Mk XXIII

Minesweeper, Sloop, Corvette, Frigate and Destroyer armament	QF 6 pounder 10 cwt QF 12 pdr 12 cwt Mk V QF 4 inch Mk IV BL 4 inch Mk IX QF 4 inch Mk XVI QF 4 inch Mk XIX QF 4.5 inch BL 4.7 inch Mk II QF 4.7 inch Mk IX & XII QF 4.7 inch Mk XI

Submarine guns	QF 12 pdr 12 cwt Mk V QF 3 inch 20 cwt QF 4 inch Mk XII & XXII

Anti-aircraft weapons	Unrotated Projectile Holman Projector 20 mm Oerlikon QF 2 pounder "pom-pom" Mk VIII 40 mm Bofors QF 3-inch 20 cwt QF 4 inch Mk V QF 4 inch Mk XVI QF 4.5 inch QF 4.7 inch Mk VIII

Light weapons	.303 Lewis machine gun .50 Vickers Mk III machine gun QF 3 pounder Vickers

Torpedoes	21 inch Mk VII 21 inch Mk VIII 21 inch Mk X 21 inch Mk XI 24.5 inch Mk I

Anti-submarine weapons	Thornycroft depth charge thrower Hedgehog Squid

Small craft armament	Molins 6 pounder Vickers K machine gun 18 inch torpedo

Foreign-sourced weapons	20 mm Oerlikon 40 mm Bofors 3-inch 23 caliber gun (US) 3-inch 50 caliber gun (US) 4-inch 50 caliber Mark 9 gun (US) 5-inch 51 caliber Mark 8 gun (US) Y-gun depth charge projector (US) Mark 8 torpedo (US)

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