The 50 calibre BL 6 inch gun Mark XXIII was the main battery gun used on the Royal Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

's conventional (non-anti-aircraft) light cruiser

Light cruiser

A light cruiser is a type of small- or medium-sized warship. The term is a shortening of the phrase "light armored cruiser", describing a small ship that carried armor in the same way as an armored cruiser: a protective belt and deck...

s built from 1930 through the Second World War.

Description

It replaced the BL 8 inch Mk VIII naval gun

BL 8 inch Mk VIII naval gun

The 50 calibre BL 8 inch gun Mark VIII was the main battery gun used on the Royal Navy's County-class heavy cruisers, in compliance with the Washington Naval Treaty of 1922. This treaty allowed ships of not more than 10,000 tons standard displacement and with guns no larger than 8 inches to be...

 used on earlier Washington Naval Treaty

Washington Naval Treaty

The Washington Naval Treaty, also known as the Five-Power Treaty, was an attempt to cap and limit, and "prevent 'further' costly escalation" of the naval arms race that had begun after World War I between various International powers, each of which had significant naval fleets. The treaty was...

 cruisers. These built-up gun

Built-up gun

The term built-up gun describes a construction technique for artillery barrels. An inner tube of metal which stretches most within its elastic limit enlarges under the pressure of confined powder gases to transmit stress to outer cylinders under tension...

s consisted of a tube and 4.5 meter jacket with a hand-operated Welin breech block

Welin breech block

The Welin breech block was a revolutionary stepped, interrupted thread design for locking artillery breeches, invented by Axel Welin in 1889 or 1890...

. Cloth bags contained 14 kg (30 pound) charges of cordite

Cordite

Cordite is a family of smokeless propellants developed and produced in the United Kingdom from 1889 to replace gunpowder as a military propellant. Like gunpowder, cordite is classified as a low explosive because of its slow burning rates and consequently low brisance...

 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.

Ships mounting BL 6 inch Mk XXIII guns

Ship	Gun Installation
HMNZS Achilles	four 95-ton Mk XXI twin turrets
	four 95-ton Mk XXI twin turrets
	three 95-ton Mk XXI twin turrets
	three 95-ton Mk XXI twin turrets
	four 175-ton Mk XXIII triple turrets
	four 175-ton Mk XXIII triple turrets
	four 150-ton Mk XXII triple turrets
	three 175-ton Mk XXIII triple turrets
	four 175-ton Mk XXIII triple turrets
	four 175-ton Mk XXIII triple turrets
	three 95-ton Mk XXI twin turrets
	four 175-ton Mk XXIII triple turrets
	four 150-ton Mk XXII triple turrets
	four 150-ton Mk XXII triple turrets
	four 95-ton Mk XXI twin turrets
	four 175-ton Mk XXIII triple turrets
	four 175-ton Mk XXIII triple turrets
HMNZS Leander HMNZS Leander HMNZS Leander was a light cruiser which served with the Royal New Zealand Navy during World War II. She was the lead ship of a class of eight ships, the Leander class light cruiser and was initially named HMS Leander.- History :...	four 95-ton Mk XXI twin turrets
	four 150-ton Mk XXII triple turrets
	four 150-ton Mk XXII triple turrets
	four 175-ton Mk XXIII triple turrets
	four 95-ton Mk XXI twin turrets
	four 150-ton Mk XXII triple turrets
	three 175-ton Mk XXIII triple turrets
	four 175-ton Mk XXIII triple turrets
	three 175-ton Mk XXIII triple turrets
	four 95-ton Mk XXI twin turrets
	three 95-ton Mk XXI twin turrets
	four 95-ton Mk XXI twin turrets
	four 150-ton Mk XXII triple turrets
	four 150-ton Mk XXII triple turrets
	three 175-ton Mk XXIII triple turrets
	three 175-ton Mk XXIII triple turrets
	four 95-ton Mk XXI twin turrets
	three 175-ton Mk XXIII triple turrets

Shell trajectory

Range	Elevation	Time of flight	Descent	Impact velocity
5000 yd (4.6 km)	2° 23′	7 sec	3° 0′	1939 ft/s (591 m/s)
10000 yd (9.1 km)	6° 15′	16 sec	9° 57′	1371 ft/s (418 m/s)
15000 yd (14 km)	13° 6′	29 sec	23° 38′	1098 ft/s (335 m/s)
20000 yd (18 km)	24° 7′	47 sec	39° 52′	1087 ft/s (331 m/s)
24500 yd (22.4 km)	41° 4′	71 sec	56° 27′	1159 ft/s (353 m/s)

Surviving examples

• Y turret from HMNZS Achilles (70)
  HMNZS Achilles (70)
  HMNZS Achilles was a Leander class light cruiser which served with the Royal New Zealand Navy in World War II. She became famous for her part in the Battle of the River Plate, alongside HMS Ajax and HMS Exeter....
  
   is preserved at the entrance to Devonport Naval Base
  Devonport Naval Base
  Devonport Naval Base is the home of the Royal New Zealand Navy, located at Devonport, New Zealand on Auckland's North Shore. It is currently the only base of the navy that operates ships, and was a navy base from as far back as 1841...
  
  , Auckland, New Zealand
• Guns and turrets are preserved on museum ship HMS Belfast (C35)
  HMS Belfast (C35)
  HMS Belfast is a museum ship, originally a Royal Navy light cruiser, permanently moored in London on the River Thames and operated by the Imperial War Museum....
  
  in London, UK

External links

• Tony DiGiulian, Britain 6"/50 (15.2 cm) BL Mark XXIII