|BL 12-inch Mk XI and Mk XII gun|
|Place of origin||United Kingdom|
|Wars||World War I|
|Manufacturer||Vickers William Beardmore and Company|
|Barrel length||50 ft (15.24 m) bore (50 calibers)|
|Shell||850 lb (385.6 kg) Lyddite, Armour-piercing, Shrapnel|
|Calibre||12 inches (304.8 mm)|
|Muzzle velocity||2,825 ft/s (861 m/s)|
|Maximum firing range||19,380 m (21,190 yd)|
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:
- St. Vincent-class battleships laid down 1907, commissioned 1910
- HMS Neptune laid down 1909, commissioned 1911
Mk XII guns were mounted on:
- Colossus-class battleships laid down 1909, commissioned 1911
Weapons of comparable role, performance and eraEdit
- Britain used Roman numerals to denote Marks (models) of ordnance until after World War II. These were the eleventh and twelfth models of BL 12-inch guns.
- 850 lb shells : Treatise on Ammunition, 1915
- 2825 ft/second with 4 CRH 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
- Tony DiGiulian, British 12"/50 (30.5 cm) Marks XI, XI* and XII