BL 15 inch Mk I naval gun

BL 15 inch Mark I

As mounted on monitor HMS Terror, 1915
Type naval gun
Place of origin United Kingdom
Service history
In service 1915-1959
Used by United Kingdom
Wars WWI, WWII, Cold War
Production history
Designed 1912
Manufacturer see text
Produced 1912-1918
Number built 186
Weight 100 long tons (100 t)[1]
Length 650.4 inches (16.52 m)[1]

Shell separate charges and shell
Shell weight 1,938 pounds (879 kg)
Calibre 15-inch (381.0 mm)
Recoil 46 inches (1.2 m)[1]
Rate of fire 2 rounds per minute
Muzzle velocity 2,458 feet per second (749 m/s)
Maximum firing range 33,550 yards (30,680 m) (Mk XVIIB or Mk XXII streamlined shell @ 30°)[2] HMS Vanguard - 37,870 yards (34,630 m) @ 30°, with supercharges.

The BL 15 inch Mark I succeeded the 13.5-inch (340 mm) gun. It was the first British 15 inch (381 mm) gun design and the most widely used and longest lasting of any British designs, and arguably the most efficient heavy gun ever developed by the Royal Navy. It was deployed on capital ships from 1915 until 1959, and was a key Royal Navy gun in both World Wars.


This gun was an enlarged version of the successful BL 13.5 inch Mk V naval gun, specifically intended to arm the new Queen Elizabeth-class battleships as part of the British response to the new generation of Dreadnought battleships Germany was building during the naval arms race leading up to World War I. The normal slow and cautious prototype and testing stages of a new gun's development were bypassed, and it was ordered straight from the drawing board due to the urgency of the times. In the event it met all expectations and was a competitive battleship main armament throughout both World Wars. According to an American report produced after World War II, the British 15 inch Mk I was the most reliable and accurate battleship main armament of the war, though other guns and mountings had superior individual features.[3]

Diagram showing gun barrel construction

The barrel was 42 calibres long (i.e., 15 in x 42 = 630 in) and was referred to as "15 inch/42". This wire-wound gun fired a 1938 lb (879 kg) Mk XVIIB shell at a muzzle velocity of 2,458 ft/s (749 m/s).[2]

The battlecruiser HMS Hood had its Mk I guns in a unique mounting, designated Mk II. Incorporating experience from the Battle of Jutland, the Mk II mounting had a maximum elevation of 30°, thus increasing the maximum range.[4] In the 1930s a modification of the Mk I mounting, designated the Mk I (N), was introduced for use in those capital ships that were completely reconstructed. The Mk I (N) mounting also increased the maximum elevation from 20° to 30°.[5] Maximum range in shipboard mountings was 33,550 yards (30,680 m) (30° elevation).[2] During World War II older battleships with gun elevation limited to 20° were supplied with supercharges to increase their maximum range to 29,930 yards (27,370 m) at 2638 ft/s (804 m/s) using the Mk XVIIB or Mk XXII projectile, while HMS Vanguard could range to 37,870 yards (34,630 m) while using supercharges at a gun elevation of 30°.[2] Coastal artillery mountings with higher elevations could reach 44,150 yards (40,370 m). The firing life of a 15 inch gun was approximately 335 full charge firings using standard charges, after which it had to be re-lined.[6]


In battle

The BL 15 inch Mark I gun proved its effectiveness at the Battle of Jutland in 1916, scoring hits out to 19,500 yards, a record for naval gunnery at that time.[7]

In World War II the gun was responsible for the longest range shell-hit ever scored by one battleship on another in combat. At the Battle of Calabria on 9 July 1940, HMS Warspite gained a hit on the Italian battleship Giulio Cesare with her first salvo at 26,400 yards.[8]


These guns were used on several classes of battleships from 1915 until HMS Vanguard, the last battleship to be built for the Royal Navy, completed in 1946.

Warships with the BL 15 inch Mark I gun:

Coastal batteries

Animation representing the loading cycle of the Mark I turret for the BL 15 inch Mark I.
Aft guns of HMS Hood trained forward to port, 1926
One of Singapore's 15 inch coastal defence guns elevated for firing


Two 15-inch guns outside the Imperial War Museum; the nearer gun from HMS Ramillies, the other from HMS Roberts.

186 guns were manufactured between 1912 and 1918.[9] They were removed from ships, refurbished, and rotated back into other ships over their lifetime.

Two guns, one formerly from HMS Ramillies (left gun) and the other originally mounted in HMS Resolution, but later moved to HMS Roberts (right gun), are mounted outside the Imperial War Museum in London.

World War II ammunition

108 lb Cordite cartridge ¼ charge
AP shell Mk XXII BNT
AP shell and cap, as fired by HMS Malaya into Genoa on 9 February 1941
An AP shell in the process of being hoisted to the gun breech, Singapore 1940

See also

Weapons of comparable role, performance and era


  1. 1 2 3 Ian Buxton, p. 181.
  2. 1 2 3 4 John Campbell, p. 25.
  3. Raven and Roberts, p. 411
  4. Raven and Roberts, p. 65
  5. Raven and Roberts, p. 226
  6. Roskill, p. 89.
  7. Burt, p. 73
  8. Burt, p. 133
  9. Ian Buxton, p. 179.


  • Burt, R. A. (2012). British Battleships, 1919–1939 (2nd ed.). Annapolis, Maryland: Naval Institute Press. ISBN 978-1-59114-052-8. 
  • Buxton, Ian Lyon (1978). Big Gun Monitors. Tynemouth: World Ship Society. ISBN 0-905617-06-1. 
  • Campbell, John (1985). Naval Weapons of World War II. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-459-4. 
  • Raven, Alan; Roberts, John (1976). British Battleships of World War Two: The Development and Technical History of the Royal Navy's Battleship and Battlecruisers from 1911 to 1946. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-817-4. 
  • Roskill, Captain Stephen Wentworth (1974). H.M.S. Warspite: The Story of a Famous Battleship. London: Futura Publications. ISBN 0-86007-172-3. 

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