BL 14 inch Mk VII naval gun

BL 14 inch Mark VII
Gunners and forward turrets of HMS Duke of York after the Battle of North Cape
Type	Naval gun
Place of origin	UK
Service history
In service	1940-1945
Used by	UK
Production history
Designed	1937
No. built	78
Specifications
Weight	80.26 metric tons (176,900 lb)
Barrel length	53 ft 6 in (16.31 m) bore (45 calibres)
Shell	1,590 lb (720 kg)
Calibre	14 inches (355.6 mm)
Elevation	Naval: 41° Coastal: 45°
Rate of fire	2 rounds per minute
Muzzle velocity	Standard Charge: 2,400 ft/s (730 m/s) (25% wear), 2,483 ft/s (757 m/s) (new gun)
Maximum firing range	36,500 yd (33,400 m) at 40.7° (25% wear) or 38,600 yd (35,300 m) at 40° with new linings

The BL 14 inch Mk VII naval gun was a breech loading (BL) gun designed for the battleships of the Royal Navy in the late 1930s. This gun armed the King George V-class battleships during the Second World War.

The choice of calibre was limited by the Second London Naval Treaty, an extension of the Washington Naval Treaty which set limits on the size armament and number of battleships constructed by the major powers. After disappointing experiences with the combination of high velocity but relatively light shell in the BL 16 inch /45 naval gun of the Nelson-class battleships, the British reverted to the combination of lower velocities and (relatively) heavier shells in this weapon.

The built-up gun was of an all-steel construction, using a radial expansion design; this was an advance on earlier British heavy guns, which employed a wire-wound technology. The resulting gun was lighter, less prone to droop, more accurate and had a significantly longer barrel life. The estimated barrel life was 340 effective full charges. The new 14-inch Armour Piercing (AP) 1,590-pound shell had, relative to its size, superior ballistic performance and armour-penetration compared to previous British shells, due to improvements in design and material which had taken place since World War I. The shell also carried a very large bursting charge of 48.5 lb (22.0 kg)

The choice of mounting was a mechanically complex, quadruple turret (each battleship had 2 quadruple turrets (Mark III) and one twin turret (Mark II)). The turret and ammunition-handling facilities incorporated many anti-flash measures and interlocks, improving safety but adding to complexity.

On entering operational service the turrets gained an initial reputation for unreliability, with individual guns and entire turrets jamming in action. However, it has been argued that these jams were typically caused by errors in drill, either due to lack of gun crew training, as was the case when the newly commissioned HMS Prince of Wales engaged the Bismarck in the Battle of the Denmark Strait (1941), or due to crew fatigue resulting from the prolonged nature of the engagement, as was the case when HMS King George V engaged Bismarck in 1941 and HMS Duke of York engaged Scharnhorst in the Battle of North Cape (1943). In the latter battle Duke of York fired 52 broadsides, of these 31 straddled the target and a further 16 fell within 200 yards - an excellent performance, even when radar-control is taken into account.