BL 13.5 inch Mk V naval gun

BL 13.5 inch Mk V gun
Rear turrets of HMS Thunderer
Type	Naval gun
Place of origin	United Kingdom
Service history
In service	1912 - 1940s (as railway gun)
Used by	United Kingdom
Wars	World War I World War II
Production history
Designer	Vickers
Designed	1909
Variants	Mk V(L) Mk V(H) Mk VI
Specifications
Barrel length	Bore 50 ft 6 in (15.392 m) (45 cal)
Shell	H: 1,400 lb (635.03 kg) L: 1,250 lb (566.99 kg) HE, AP
Calibre	13.5-inch (342.9 mm)
Elevation	Naval: 0° - 20° Railway: 0° - 40°
Muzzle velocity	H: 2,491 ft/s (759 m/s) L: 2,582 ft/s (787 m/s)
Maximum firing range	H: 23,740 yards (21,710 m) at 20° L: 23,820 yards (21,780 m) at 20° H: 40,600 yards (37,120 m) at 40° (World War II railway gun, with Super Charge)

The BL 13.5 inch Mk V gun was a British heavy naval gun, introduced in 1912 as the main armament for the new super-dreadnought battleships of the Orion class. The calibre was 13.5 inches (343 mm) and the barrels were 45 calibres long i.e. 607.5 inches (15.43 m). The guns were greatly superior and unrelated to the earlier 13.5-inch (30-calibre) Mk I to Mk IV guns used on the Admiral, Trafalgar and Royal Sovereign classes completed between 1888 and 1896.

The gun was developed in response to the relative failure of the British high-velocity 12-inch Mk XI and XII guns. Unlike Germany, which developed and deployed successful high-velocity 12-inch guns, Britain in this case switched to guns firing larger and heavier shells at lower velocity which could achieve similar performance in range and armour penetration but could deliver a heavier explosive charge on impact.

The gun was wire-wound and weighed approximately 168,000 lb (76 tonnes) (excluding the breech), and in its original form fired a 1,250 lb (567 kg) armour-piercing capped (APC) or high-explosive (HE) round a distance of 23,800 yards (21,800 m) at a 20-degree elevation.

Due to the excellent characteristics of the gun, it was decided to increase the weight of shell to 1,400 lb (635 kg), with an increased firing charge to achieve about the same range. The gun firing the lighter shell was designated Mark V(L) (for "light") by the Royal Navy, and the 1,400 lb version Mark V(H) (for "heavy"). A very similar 1,400 lb gun, designed for the Ottoman battleship Reşadiye, received the designation Mark VI when the ship was requisitioned by the British government after the outbreak of the First World War, eventually being commissioned as HMS Erin.