BL 12-inch Mk X naval gun

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BL 12-inch gun Mk X
HMSDreadnought gunsLOCBain17494.jpg
Type Naval gun
Place of origin United Kingdom
Service history
In service 1906 – 1923
Wars World War I
Production history
Designer Vickers
Manufacturer Vickers
Weight 57 tons barrel & breech[1]
Barrel length 45 feet (13.72 m) bore (45 cal)

Shell 850 pounds (385.6 kg) Lyddite, Armour-piercing, Shrapnel[2]
Calibre 12 inches (304.8 mm)
Breech Welin interrupted screw
Muzzle velocity 2,700 ft/s (823 m/s)[3]
Maximum firing range 22,860 m (25,000 yd)[4]

The BL 12 inch Gun Mark X[note 1] was a British 45-calibres naval gun which was mounted as primary armament on battleships and battlecruisers from 1906. It first appeared on HMS Britannia.


HMS Agamemnon has her guns replaced during a refit at Malta in May–June 1915
Ramming shell on HMAS Australia, December 1918

Mk X continued the trend of lengthening gun barrels as far as new construction methods would permit, in order to allow more cordite propellant to be used to attain higher projectile velocities. Mk X increased the bore length from Mk IX's 480 to 540 in (12 to 14 metres), increasing muzzle velocity from 2,600 to 2,700 ft/s (790 to 820 m/s).

Subsequent British attempts to further increase the power of 12-inch guns led to failure with the 50-calibre Mk XI and Mk XII guns; the Mk X was the last successful 12-inch British gun.

Naval use

Mk X Guns were mounted in the following ships which served throughout World War I :

World War I use ashore

From 1917 several Mk X guns were deployed ashore on the section of the Belgian coast still held by the Allies, near Nieuwpoort. They were part of the "Royal Naval Siege Guns" under the command of Admiral Sir Reginald Bacon, and were used for attacking German heavy gun batteries.


HMAS Australia 12 inch shells Closeup.JPG
65 lb Cordite Cartridge ¼ charge : i.e. 4 such cartridges were normally loaded to fire the gun
Mk VIIA Common Pointed shell with Cap (CPC) filled with gunpowder, 1912
World War I Shells. Left to Right :
  • Mk XA Capped Armour-Piercing shell filled with Trotyl (TNT)
  • Shrapnel
  • Mk 6A Capped Common pointed shell filled with Shellite 70/30

See also

Weapons of comparable role, performance and era


  1. ^ Mark X = Mark 10. Succeeding versions were Mark XI (11) and XII (12). Britain used Roman numerals to denote Marks (models) of ordnance until after World War II


  1. ^ "BR 12in 45cal BL Mk X". Retrieved 9 November 2018.
  2. ^ 850 lb shells : Treatise on Ammunition, 1915
  3. ^ 2700 ft/second : As quoted in "Range Tables for His Majesty's Fleet, 1910. February, 1911"; with 260 lb cordite MD size 45 propellant : Treatise on Ammunition, 1915
  4. ^ 22,860 metres quoted at : This is understood to be the maximum possible range at 45° elevation, which was possible for siege mountings on land but not for naval mounts


External links

  • Tony DiGiulian, British 12"/45 (30.5 cm) Mark X
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