The BL 12-inch Mark XI and Mark XII gun were British breech loading (BL) naval guns of 50-calibres length mounted as primary armament on dreadnought battleships from 1910.

History

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 2700 ft/s to 2825 ft/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:

Weapons of comparable role, performance and era