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BL 12 inch gun Mk XI, Mk XII
HMS Vanguard aft guns USNHC NH 52619.jpg
Aft Mk XI guns of HMS Vanguard
Type Naval gun
Place of origin  United Kingdom
Service history
In service 1910 - 1920
Wars World War I
Production history
Designer Vickers
Manufacturer Vickers
Barrel length 50 ft (15.24 m) bore (50 cal)

Shell 850 lb (385.6 kg) Lyddite, Armour-piercing, Shrapnel[1]
Calibre 12 inches (304.8 mm)
Muzzle velocity 2,825 ft/s (861 m/s)[2]
Maximum range 19,380 m (21,190 yd)[3]

The BL 12 inch Gun Mark XI and Mark XII were British 50-calibres naval guns that were mounted as primary armament on dreadnought battleships from 1910.


Vice-Admiral Doveton Sturdee in front of the Mk XII guns of a wing turret on HMS Hercules

Mk XI had a longer (50 calibres, 600 inches) barrel than the previous Mk X gun (45 calibres), and was an attempt to increase the muzzle velocity, and hence armour-piercing capability and range, of a 12-inch gun. The muzzle velocity increased from 2,700 feet per second (820 m/s) to 2,825 feet per second (861 m/s) but problems such as bore erosion, which led to short barrel life, and poor accuracy due to inconsistent cordite propellant burning, meant the gun was not entirely satisfactory. The subsequent Mk XII gun suffered from the same problems.

Instead of attempting to improve the 12-inch gun, the British developed the 13.5-inch Mk V gun of 45-calibres, as it could achieve greater range at lower muzzle velocities due to its larger shell.

Mk XI guns were mounted in the following ships :

Mk XII guns were mounted in the following ships :

Surviving examples

See also

Weapons of comparable role, performance and era


  1. 850 lb shells : Treatise on Ammunition, 1915
  2. 2825 ft/second with 4 C.R.H. 850 lb projectile : As quoted in Range Tables for His Majesty's Fleet, Vol. I., 1918 9.2-Inch Guns and Above April, 1918 2825 ft/second using 307 lb cordite MD size 45 propellant : Treatise on Ammunition, 1915


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