BL 6 inch Mk XXIII naval gun

The 50 calibre BL 6 inch gun Mark XXIII was the main battery gun used on the Royal Navy and British Commonwealth's conventional (non-anti-aircraft) light cruisers built from 1930 through the Second World War, and passed into service with several other navies when ships were disposed of after the end of the War.

Description
It replaced the BL 8 inch Mk VIII naval gun used on earlier Washington Naval Treaty cruisers. These built-up guns consisted of a tube and 4.5 metre jacket with a hand-operated Welin breech block. Cloth bags contained 14 kg (30 pound) charges of cordite or flashless (NQFP) powder for a 51-kg (112-pound) projectile. Useful life expectancy was 1100 effective full charges (EFC) with standard cordite and 2200 EFC with NQFP per barrel. The typical maximum rate of fire was eight rounds per gun, per minute. The Mk XXIII turret design was improved through a "long trunk" ammunition hoist, which reduced the crew requirements and increased the speed of the ammunition hoists. As in the MK XXII turret loading could be accomplished at any angle up to 12.5 degrees gun elevation. A RN gunnery officer on HMS Bermuda gave details of the loading cycle which could be attained in the Mk XXIII turret with a well trained crew: "...a loading cycle of four and a half to 5 seconds was attained at low elevation, another two to three seconds being required with the guns elevated for long range. The time would lengthen as fatigue set in, but was creditable..."

Weapons of comparable role, performance and era

 * 15 cm SK C/25 : German equivalent light cruiser gun, operating at higher velocity
 * 15.5 cm/60 3rd Year Type : slightly larger Japanese equivalent
 * 6 inch 47 caliber : US equivalent light cruiser gun

Surviving examples

 * Y turret from HMNZS Achilles (70) is preserved at the entrance to Devonport Naval Base, Auckland, New Zealand
 * Guns and turrets are preserved on museum ship HMS Belfast (C35) in London, UK