BL 15 inch Mk I naval gun

The BL 15 inch Mark I succeeded the 13.5 in 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.

Design
This gun was an enlarged version of the successful BL 13.5 inch Mk V naval gun, specifically intended to arm the new s 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.

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 (785 m/s). Maximum range in shipboard mountings was 33,550 yards (30,680 m) (30 degrees elevation). During World War II older battleships with gun elevation limited to 20 degrees 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 degrees. 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.

Warships
These guns were used on several classes of battleships from 1915 until HMS Vanguard (23), the last battleship to be built for the Royal Navy, completed in 1946.

Warships with the BL 15 inch Mark I gun:
 * s (Five ships with eight guns each)
 * s (Five ships with eight guns each)
 * s (Two ships with six guns each)
 * HMS Hood (51) - battlecruiser (Eight guns)
 * s (Two ships with four guns each)
 * s (Two ships with two guns each)
 * s (Two ships with two guns each)
 * s (Two ships with two guns each)
 * HMS Vanguard (23) - battleship (Eight guns in mountings taken from Courageous and Glorious)

Coastal batteries

 * Two coastal guns ("Clem" and "Jane") were mounted near Wanstone Farm in Kent in the 1940s.
 * Five guns were mounted in Singapore at Johore battery and Buona Vista Battery in the 1930s.
 * In the late 1920's Spain purchased four guns in single turrets to guard Cartagena. These are still in place and the two batteries they form part of, are being renovated, and open to the public.

Production
186 guns were manufactured between 1912 and 1918. They were removed from ships, refurbished, and rotated back into other ships over their lifetime.
 * Elswick Ordnance Company, Elswick, Newcastle: 34
 * Armstrong Whitworth, Openshaw, Manchester: 12.
 * William Beardmore & Company, Parkhead, Glasgow: 37
 * Coventry Ordnance Works, Coventry: 19
 * Royal Gun Factory, Woolwich: 33
 * Vickers, Son and Maxim, Sheffield: 49

Two guns, one formerly from HMS Ramillies (07) (left gun) and the other originally mounted in HMS Resolution (09), but later moved to HMS Roberts (F40) (right gun), are mounted outside the Imperial War Museum in London. 

Weapons of comparable role, performance and era

 * 38 cm SK L/45 "Max" - German Counterpart
 * Cannone navali da 381/40 : Italian counterpart