BL 6-inch Mk XXIII naval gun

Ordnance BL 6 inch gun Mk XXIII
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
No. built	469[1]
Specifications
Mass	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

The gun 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 of a barrel was 1,100 effective full charges (EFC) with standard cordite and 2,200 EFC with NQFP.[1] The typical maximum rate of fire was eight rounds per gun, per minute.[2] There were three mountings: the two-gun Mk XXI, the three-gun Mk XXII and the three-gun Mk XXIII. Depending on the mount elevation limits differed. The Mk XXI turret elevation limits were +60 degrees to −5 degrees, and the Mk XXII turret elevation limits were +45 degrees to −5 degrees. Loading could be accomplished at any angle up to +12.5 degrees, although the preferred loading angle was between +7 and +5 degrees for all three mounts. The Mk XXI and XXII mounts used a "short trunk" ammunition hoist while the Mk XXIII used a "long trunk" ammunition hoist system, which reduced the crew requirements and increased the speed of the hoists.[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

Inside a twin Mark XXI turret aboard HMS Orion, a Leander-class cruiser.

Shell trajectory

Range[1]	Elevation	Time of flight	Descent	Impact velocity
5,000 yd (4.6 km)	2° 23′	7 sec	3° 0′	1,939 ft/s (591 m/s)
10,000 yd (9.1 km)	6° 15′	16 sec	9° 57′	1,371 ft/s (418 m/s)
15,000 yd (14 km)	13° 6′	29 sec	23° 38′	1,098 ft/s (335 m/s)
20,000 yd (18 km)	24° 7′	47 sec	39° 52′	1,087 ft/s (331 m/s)
24,500 yd (22.4 km)	41° 4′	71 sec	56° 27′	1,159 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, later INS Delhi (1948), is preserved at the entrance to Devonport Naval Base, Auckland, New Zealand.
A second turret from INS Delhi, is preserved at the Indian Military Academy, Dehradun.
12 guns and four turrets are preserved on the museum ship HMS Belfast in London, UK
A number of Mark XXIIIs can also be found at English Heritage or other 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.
One is on display at The Historic Dockyard Chatham, Kent, England. It is at the head of No.3 Dry Dock. Royal Navy 6" breech-loading Mk.XXIIIL WWII cruiser gun and the barrel is on 6" P Mk.XI (or P. XII. REGD. No 15) proof mounting as used at Proof and Experimental Establishment (P&EE), Shoeburyness, Essex, 1948-87.

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

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 0-85059-578-9.
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

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

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[2] 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.

[Campbell-1] Campbell 1985 pp.34-36

[3] O.U. 6359A, Handbook for 6-Inch, B.L., Mark XXIII Guns on Triple, Mark XXII Mounting, 1937, page 8.

[4] Campbell, Naval Weapons of WWII, p.35-36.

[5] Brooke, p.200

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 5.5-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-pounder 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-pounder 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)