BL 6-inch Mk XII naval gun

The BL 6-inch Mark XII naval gun[8] was a British 45 calibre naval gun which was mounted as primary armament on light cruisers and secondary armament on dreadnought battleships commissioned in the period 1914–1926, and remained in service on many warships until the end of World War II.

BL 6-inch Mk XII naval gun
Casemate gun on HMS Warspite after the Battle of Jutland, June 1916
TypeNaval gun
Place of originUnited Kingdom
Service history
In service1914–2011
Used byBritish Empire
Production history
No. built463
Mass15,512 pounds (7,036 kg) barrel & breech[1]
Barrel length270 inches (6.858 m) bore (45 cal)[2]

Shell100 pounds (45.36 kg) Lyddite, Armour-piercing, Shrapnel[3]
Calibre6 inches (152.4 mm)
BreechWelin interrupted screw
RecoilHydro-spring, 16.5 inches (420 mm)[4]
Rate of fire5-7 rpm
Muzzle velocity2,825 feet per second (861 m/s)[6]
Maximum firing range19,660 metres (21,500 yd)[7]


This was a high-velocity naval gun consisting of inner "A" tube, "A" tube, wound with successive layers of steel wire, with a jacket over the wire.[9]

It superseded the 45-calibres Mk VII gun and the longer 50-calibres Mk XI gun which had proved unwieldy in light cruisers due to its length, and was Britain's most modern 6-inch naval gun when World War I began.

It was superseded as secondary armament on new battleships in the 1920s by the 50-calibre 6-inch Mk XXII gun, and as main armament on new light cruisers in the 1930s by the 50-calibre 6-inch Mk XXIII gun.

Guns were mounted in the following ships :

Coast defence gun

During WWII some Mk XII guns were used in emergency coast defense batteries.[10]

Notable actions


This gun generated a higher pressure in the chamber on firing compared to preceding 6-inch guns such as Mk VII and Mk XI. This necessitated use of special shells capable of withstanding a pressure of 20 tons per square inch on firing, which had "Q" suffixed to the name. World War I shells were marked "A.Q." denoting special 4 CRH shells for this gun.[1]

See also

Weapons of comparable role, performance and era

Surviving examples

Notes and references

  1. Handbook, 1917, Page 5
  2. Handbook, 1917, Page 7
  3. 100 lb shells: Treatise on Ammunition, 1915
  4. Handbook, 1917, Page 6, 23-26
  5. 30° elevation was possible with P.XIII mountings used on light cruisers; 20° elevation was possible on some P.VII* mountings used on light cruisers; 14° elevation was possible with P.IX mountings used on battleships; 15° was possible with P.VII mountings used on light cruisers. Handbook, 1917, Pages 5, 31, 41, Plates 6, 24, 35
  6. 2,825 feet per second using 27 lb 2 oz cordite MD size 19 propellant was the figure used in range tables. New guns were quoted with a muzzle velocity of 2,845 feet per second. Handbook, 1917, Page 5
  7. "Gun Model: BR 6in 45cal BL Mk XII". navalhistory. Retrieved 6 September 2014.
  8. Mark XII = Mark 12 : Britain denoted Marks (models) of guns with Roman numerals until after World War II. This was the twelfth model of British BL 6-inch gun.
  9. Handbook, 1917, page 5, 6
  10. "Britain 6"/45 (15.2 cm) BL Mark XII and Mark XX". Retrieved 6 September 2014.


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