BL 6-inch Mk XXIII naval gun

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.

Ordnance BL 6 inch gun Mk XXIII
Forward triple-gun turrets of HMS Belfast, March 2005
TypeNaval gun
Place of originUnited Kingdom
Service history
In service1931 - 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
WarsSecond World War
Korean War
Production history
No. built469[1]
Mass7 tonnes[1]
Barrel length300 inches (7.6 meters)[1]

Shell112 pounds (51 kg)
Calibre6-inch (152.4 mm)[1]
Muzzle velocity2760 feet per second (840 m/s)[1]
Maximum firing range25,480 yd (23,300 m) at 45 degrees elevation[1]


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 1100 effective full charges (EFC) with standard cordite and 2200 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 ammunition 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

Shell trajectory

Range[1] Elevation Time of flight Descent Impact velocity
5000 yd (4.6 km)  23′ 7 sec  0′ 1939 ft/s (591 m/s)
10000 yd (9.1 km)  15′ 16 sec  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)


See also

Weapons of comparable role, performance and era

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 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 located in the courtyard of American Turners in Louisville, Kentucky


  1. 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.


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


  • 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.
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