BL 12-inch Mk XI – XII naval gun

BL 12-inch Mk XI and Mk XII gun
HMS Hercules (aft deck).jpg
Aft Mk XII guns of HMS Hercules
TypeNaval gun
Place of originUnited Kingdom
Service history
In service1910–1922
WarsWorld War I
Production history

Armstrong WhitworthCoventry Ordnance Works

William Beardmore and Company
Barrel length50 ft (15.24 m) bore (50 calibers)

Shell850 lb (385.6 kg) Lyddite, Armour-piercing, Shrapnel[1]
Calibre12 inches (304.8 mm)
Muzzle velocity2,825 ft/s (861 m/s)[2]
Maximum firing range19,380 m (21,190 yd)[3]

The BL 12-inch Mark XI and Mark XII gun[note 1] were British breech loading (BL) naval guns of 50-calibres length 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

In an effort to increase the armour-piercing capability and range of a 12-inch gun, the 50 calibres/600 inches Mk XI's barrel was 5 calibres/60 inches longer than the previous Mk X gun's 45 calibres. As a result, muzzle velocity increased from 2,700 feet per second (820 m/s) to 2,825 feet per second (861 m/s), but bore erosion, which led to short barrel life, and poor accuracy due to inconsistent cordite propellant burning, hampered the gun. The Mk XII derived from it suffered from the same problems.

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

Mk XI guns were mounted on:

Mk XII guns were mounted on: