The BL 4-inch Mk IX naval gunMk IX = Mark 9. Britain used

Roman numerals Roman numerals are a numeral system that originated in ancient Rome and remained the usual way of writing numbers throughout Europe well into the Late Middle Ages. Numbers are written with combinations of letters from the Latin alphabet, eac ...

to denote Marks (models) of ordnance until after World War II. Mark IX indicates this was the ninth model of BL 4-inch gun. was a British medium-velocity naval gun introduced in 1917 as secondary armament on the battlecruisers and "large light cruisers", but which served most notably as the main armament on s throughout

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

History

World War I

HMS Repulse 1916-1917 Firth of Forth NH47372 clip

The gun was based on the barrel of the QF 4-inch Mk V and the breech mechanism of the BL 4-inch Mk VIII and was first introduced in World War I on

capital ship The capital ships of a navy are its most important warships; they are generally the larger ships when compared to other warships in their respective fleet. A capital ship is generally a leading or a primary ship in a naval fleet. Strategic i ...

s as secondary armament in triple-gun mountings, intended to provide rapid concentrated fire. This turned out to be unworkable in practice. ''

Jane's Fighting Ships ''Janes Fighting Ships'' is an annual reference book of each country's warship, navy and coast guard, along with their weapons and aircraft. Included are ship names, construction data, size, speed, range, complement, engineering, armament, a ...

'' of 1919 commented, "4-inch triples are clumsy and not liked. They are not mounted in one sleeve; have separate breech mechanism, a gun crew of 23 to each triple". Guns were thereafter used in single-gun mountings, typically on smaller ships as the main armament.

World War II

, the gun was employed on many small warships such as s and

minesweeper A minesweeper is a small warship designed to remove or detonate naval mines. Using various mechanisms intended to counter the threat posed by naval mines, minesweepers keep waterways clear for safe shipping. History The earliest known usage of ...

s, primarily for action against surfaced submarines. This was the last BL 4 inch gun in British service: all subsequent guns have used charges in metal cartridges "QF". It was succeeded on new small warships built in World War II by the QF 4-inch Mk XIX gun which fired a slightly heavier shell at much lower velocity and had a high-angle mounting which added anti-aircraft capability.

Surviving examples

* On board , the last surviving , at

Halifax, Nova Scotia Halifax is the capital and most populous municipality of the Provinces and territories of Canada, Canadian province of Nova Scotia, and the most populous municipality in Atlantic Canada. As of 2024, it is estimated that the population of the H ...

, Canada * A gun at the entrance to the marina in

Hull Hull may refer to: Structures * The hull of an armored fighting vehicle, housing the chassis * Fuselage, of an aircraft * Hull (botany), the outer covering of seeds * Hull (watercraft), the body or frame of a sea-going craft * Submarine hull Ma ...

, UK * A gun at Port Isaac, Cornwall, UK *

Leith Harbour Leith Harbour (), also known as Port Leith, was a whaling station on the northeast coast of South Georgia Island, South Georgia, established and operated by Christian Salvesen, Christian Salvesen Ltd, Edinburgh. The station was in operation f ...

South Georgia South Georgia is an island in the Atlantic Ocean, South Atlantic Ocean that is part of the British Overseas Territories, British Overseas Territory of South Georgia and the South Sandwich Islands. It lies around east of the Falkland Islands. ...

Notes

References

Bibliography

* Tony DiGiulian
British 4"/45 (10.2 cm) BL Marks IX and X
* {{DEFAULTSORT:BL 04-inch Mk 09 gun Naval guns of the United Kingdom World War I naval weapons of the United Kingdom World War II naval weapons of the United Kingdom 100 mm artillery