BL 6 inch Mk XI naval gun

BL 6 inch gun Mk XI
Gunnery exercise on HMAS Melbourne circa. 1913
Type	Naval gun Coast defence gun
Place of origin	United Kingdom
Service history
In service	1906 - 1950s
Wars	World War I World War II
Production history
No. built	177
Variants	Mk XI
Specifications
Weight	19,237 lbs (8,726 kg)
Barrel length	300 inches (7.620 m) bore (50 cal)
Shell	100 pounds (45.36 kg) Lyddite, Armour-piercing, Shrapnel
Calibre	6 inches (152.4 mm)
Muzzle velocity	2,900 feet per second (884 m/s)
Maximum firing range	18,000 yards (16,000 m) @ 22.5°

The BL 6 inch Gun Mark XI was a British 50 calibres high-velocity naval gun which was mounted as primary armament on cruisers and secondary armament on pre-dreadnought battleships from 1906 onwards.

The gun with its increased length of 50 calibres gave improved firepower over the current 6-inch Mk VII gun of 45 calibres. However, its increased length and weight made it unwieldy in the current manually operated shipboard mountings on light cruisers, which did not provide a steady platform. Britain reverted to 45-calibres guns in new warships from 1914 onwards with the BL 6 inch Mk XII gun. Of the 177 produced 126 remained for Royal Navy use in 1939.

Guns were mounted in the following ships :

The Mk XI gun was emplaced for coast defence in South Africa and particularly in Australia leading up to World War II, and remained in service until the 1950s. Guns in Australia came from the decommissioned World War I cruisers HMAS Sydney, HMAS Melbourne and HMAS Brisbane and were emplaced in northern Australia and Torres Strait to defend against possible attack by Japan, and on Rottnest Island WA, Brisbane and the Sydney harbour and Port Kembla defences.