BL 6 inch Mk XXIII naval gun
|Ordnance BL 6 inch gun Mk XXIII|
Forward triple-gun turrets of HMS Belfast, March 2005
|Place of origin||United Kingdom|
|In service||1931 - 1985|
|Used by|| Royal Navy
Royal Australian Navy
Royal New Zealand Navy
Royal Canadian Navy
Republic of China Navy
People's Liberation Army Navy
|Wars||Second World War
|Barrel length||300 inches (7.6 meters)|
|Shell||112 pounds (51 kg)|
|Calibre||6-inch (152.4 mm)|
|Muzzle velocity||2760 feet per second (840 m/s)|
|Maximum firing range||25,480 yd (23,300 m) at 45 degrees elevation|
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.
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. The typical maximum rate of fire was eight rounds per gun, per minute.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 ammunition hoists. 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..." 
Ships mounting BL 6 inch Mk XXIII guns
|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|
|Range||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)|
Weapons of comparable role, performance and era
- 15 cm SK C/25 : German equivalent light cruiser gun, operating at higher velocity
- 15 cm SK C/28 : approximate German equivalent
- 15.5 cm/60 3rd Year Type : slightly larger Japanese equivalent
- 6 inch 47 caliber : US equivalent light cruiser gun
- 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 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.
- 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 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
- 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.
|Wikimedia Commons has media related to BL 6 inch Mk XXIII naval gun.|
- Tony DiGiulian, Britain 6"/50 (15.2 cm) BL Mark XXIII