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Ordnance QF 4.5 inch gun Mk I, II, III, IV, V
4,5inch L45 11,3cm tooheavyammo beautiful, on imp cl.jpg

Mk III guns in BD 'RP10' Mk II mountings on Implacable-class aircraft carrier
Type Naval gun
Anti-aircraft gun
Place of origin United Kingdom
Service history
Used by British Commonwealth
Wars Second World War
Korean War
Falklands War
Production history
Number built Navy: c. 800
Army: 474
Barrel length Bore: 16 ft 8 in (5.08 m)
45 calibres

Shell Fixed or Separate QF 55 pounds (24.9 kg)
Calibre 4.45-inch (113 mm)
Breech Mks I - IV: Horizontal sliding block
Mk V: Vertical sliding block
Rate of fire 12 RPM for Mk II BD mount. 16 RPM recorded for Mk III UD mount.[1]
Muzzle velocity 2,449 ft/s (746 m/s)[2]
Maximum range 20,750 yd (18,970 m) at 2,449 ft/s (746 m/s)
AA:41,000 ft (12,500 m)[2]

The QF 4.5 inch gun has been the standard medium-calibre naval gun used by the Royal Navy as a medium range weapon capable of use against surface, aircraft and shore bombardment targets since 1938. This article covers the early 45-calibre family of guns up to the 1970s. For the later unrelated 55-calibre Royal Navy gun, see 4.5 inch Mark 8 naval gun.

Like all British nominally 4.5 inch naval guns, the QF Mk I has an actual calibre of 4.45 inches (113 mm).[3][4]


From the BL Mark I gun of 1916 onwards the 4.7-inch (120-mm) calibre was the mid-calibre weapon of choice for the Royal Navy, used particularly on destroyers. Apart from some ships armed with QF 4-inch Mk V guns due to supply problems, it remained the standard weapon for destroyers up to the W-class destroyers of 1943. However, its usefulness as an anti-aircraft weapon had been limited by the failure to develop a mounting with elevation over 55°, the lack of a predictive fire control system in destroyer classes built prior to the introduction of the 4.7 inch twin mount, (see HACS) and the setting of fuzes by hand on early, prewar, mountings. Later 4.7 inch mountings used mechanical fuze setters that were identical to those used on the 4.5 inch mountings.[5]


The QF 4.5 inch L/45 was developed originally as a dual-purpose weapon with which to arm aircraft carriers and reconstructed battleships and battlecruisers. It was later developed as a new dual-purpose weapon with which to arm destroyers, supplanting the ubiquitous 4.7 inch gun. Despite the lower calibre, it actually had a heavier shell, resulting in a more powerful weapon.


Gunner with early fixed round, 1942

The nomenclature system for guns used by the Royal Navy can be somewhat confusing. The gun and mounting each have their own Mark number and a letter(s) giving additional information. QF stands for "quick firing", UD for "upper deck", BD for "between decks" and CP for "central pivot".

  • QF Mark I: adopted after failure of a 5-inch gun project and used a fixed round, which proved to be somewhat heavy for the loaders to keep up the intended firing rate. Was fitted in twin mountings UD Mark III.
  • QF Mark II: Land service used by the British Army.
  • QF Mark III: same as Mark I, except for firing mechanism. Was fitted in twin mountings BD Mark II, BD Mark II** and BD Mark IV. HMS Illustrious fired about 3000 rounds of 4.5-inch ammunition, at an average of 12 rounds per gun per minute, during one prolonged action in January 1941.[6]
  • QF Mark IV: used a two part (charge and shell) ammunition system. Designed specifically for use by small warships. Fitted in mountings BD Mark IV, CP Mark V and UD Mark VI.
  • QF Mark V: a further development of the Mark IV, designed from the outset for anti-aircraft use with remote power control (RPC, where the guns automatically train and elevate the target following the director) and a high rate-of-fire assisted by automatic ramming. Carried in the mounting UD Mark VI, with separate high-angle and low-angle hoists for the two types of ammunition (AA and SAP/HE) and a third for the cartridges. The rate of fire of the Mk V was 24 rounds per minute when power-loaded, 12-14 when hand-loaded, and up to 18 in burst mode when hand-loaded.

Some 800 naval 4.5-inch guns of various marks were built. 474 guns were built for the army, all in 1939-41.

During the 1950s, a change was made in designating the weapons systems which focussed on the gun mount rather than the gun itself. Together with a change from Roman numerals, the Gun QF Mark V on mounting BD Mark VI became simply the Mark 6. The Mark 7 was never produced as the planned Malta-class aircraft carriers they would have been used on were never built.

The majority of new escort vessels built for the Royal Navy in the 1950s and 1960s carried at least one Mark 6 mounting, with two in the Leopard-class frigates and County-class destroyers and three in the Daring-class destroyers. This gave these ships a level of firepower unprecedented only 15 years earlier. The Type 81 Tribal-class frigates were an exception, using reconditioned Mark V mounts from scrapped C-class destroyers that were fitted with RPC and known as the Mark 5* Mod 1.

The evolution of the 45-calibre 4.5 inch gun family ended with the Mark V gun / Mark 6 mounting. It has been replaced by a new weapon of original design, the 4.5 inch Mark 8 with a 55 calibre-long barrel.

Naval service

Twin mountings, Upper Deck, Mark VI on post-war Daring-class destroyer. BD-s in contrast were semi-submerged turrets used on some of the major warships.

Ships with 4.5 inch guns QF Mark I in twin mounting UD Mark III

Ships with 4.5 inch guns QF Mark III in twin mounting BD Mark II

Twin Mark III guns on Illustrious-class aircraft carrier HMS Formidable

Ships with 4.5 inch guns QF Mark III in twin mounting BD Mark II**

Ships with 4.5 inch guns QF Mark III in twin mounting BD Mark IV

Ships with 4.5 inch guns QF Mark IV in single mounting CP Mark V

Ships with 4.5 inch guns Mark 5* (rebuilt mounting CP Mark V).

Ships with 4.5 inch guns QF Mark V in twin mounting UD Mark VI (later renamed gun Mark 6)

Twin Mark 6 guns in turret from Type 12/River class HMAS Derwent

Land service

4.5 inch anti-aircraft gun and crew near Sittingbourne, Kent, January 1941

QF Mark II was a single gun mounting (Mounting Mk 1) anti-aircraft gun in static sites. The pedestal mount was bolted to concrete in an unarmoured turret, a travelling platform was available to transport the gun and mounting between positions. The first unit became operational in February 1939. These 16.5 ton anti-aircraft mountings had a max elevation angle of 80 degrees. However, most mountings were Mark 1A with an elevation range of -9.5 to 80 degrees, this enabled the gun to be dual role (AA/CD) in coastal areas, armour piercing was provided for anti-ship engagements. The guns were fitted with Magslip electrical data transfer from Predictors AA Nos 3, 5 and 10 and were probably used inially with GL radars and UB 10 18 feet base optical height & rangefinders. AA control radars evolved rapidly. The gun was laid and fuzes set by pointer matching, it is unclear the extent to which advances in 3.7-inch fire control were applied to 4.5-inch. However, mid-war Machine Fuze Setter No 10 was added, this improved the rate of fire from 8 to 10 rounds per minute and raised the effective ceiling to 34,500 feet.

Gun positions were usually in the vicinity of naval bases where they could use the naval ammunition supply. However, initially the standard fuze was an igniferous design, No 199 with a maximum running time of 30 seonds that limited performance. Subsequently No 209 a mechanical time fuze was introduced. However, it appears that VT fuzes were not issued.

Guns were usually deployed in troops of 4 as part of a two troop battery, although sections of two guns occupied some positions. Deployment included:

UK (Royal Artillery) June 1940:[7]

  • 1st AA Division - 48
  • 2nd AA Division - 40
  • 3rd AA Division - 64
  • 4th AA Division - 52
  • 5th AA Division - 24
  • 6th AA Division - 52
  • 7th AA Division - 64

(the AA divisions included 3-inch and 3.7-inch regiments in addition to 4.5-inch)

Far East January 1942:[8]

  • Singapore - 4 (Hong Kong & Singapore Artillery)

Mediterranean June 1943:[9]

  • Malta - 10

Middle East January 1943:[10]

  • Aden - 2 (Hong Kong & Singapore Artillery)
  • Port Said - 2 (Royal Malta Artillery)

West Africa Dec 1941:[11]

  • Takoradi - 6

India Dec 1941:[12]

  • Bombay - 6

Colonel Probert of the Armaments Research Department developed rifling with tapered groove depth, and the last few inches of the barrel being smoothebore. This was used with a 4.5 barrel lined down to 3.7 inches, but retaining the large chamber, hence a large propelling charge. Ordnance, QF 3.7 inch Mk 6, only on a static mounting, entered service in 1943 and continued in service until 1959. It had an effective ceiling of 45,000 feet.[13][14] The high performance of QF 3.7 inch Mk 6 and QF 5.25 inch meant that QF 4.5 inch was not retained in land service after World War II.

Surviving examples

  • Single Mk IV/CP Mk V mounting from Z-class destroyer INS Yaffo, at Clandestine Immigration and Naval Museum, Haifa, Israel.
  • Australia:
    • Twin Mk V/Mk 6 turrets on HMAS Vampire (D11) museum ship at Australian National Maritime Museum, Sydney, Australia.
    • [Twin Mk V/Mk 6 turret [1] from HMAS Stuart on display at HMAS Stirling, Garden Island (Western Australia).
    • Twin Mk V/Mk 6 turret from HMAS Derwent (DE 49) at Rockingham Naval Memorial Park, Rockingham, Western Australia.
    • Twin Mk V/Mk 6 turret [2] from HMAS Swan at Princess Royal Fortress, Albany, Western Australia. This turret is open and accessible to visitors.
    • Twin Mk V/Mk 6 turret [3] from HMAS Torrens at Princess Royal Fortress, Albany, Western Australia.
    • Twin Mk V/Mk 6 turret [4] used as a static training aid outside the Gunnery School, HMAS Cerberus, Crib Point, Australia.
    • Twin Mk V/Mk 6 turret [5] as a gate guardian at the West Head Gunnery Range, Flinders, Australia. Previously used at the gunnery range as a live training aid, the gun was last fired in 2005.
    • Twin Mk V/Mk 6 turret at the Bendigo and District RSL. Owned by the Australian Government, it is on loan from the nearby defence manufacturer Thales.[15]
    • Twin Mk V/Mk 6 turret at Australian Navy Cadets TS Bendigo at Passchendaele Barracks, Junortoun near Bendigo. As the previous location of TS Bendigo was on the Government Ordnance Factory site (now Thales Australia), it is probable it is also on loan from Thales.[16]
  • New Zealand:
  • United Kingdom:

See also

Weapons of comparable role, performance and era


  1. Hughes, p.170.
  2. 2.0 2.1 Campbell, p.51
  3. Jane's Ammunition Handbook, 1999-2000 Edition.
  4. Routledge 1994, page 51
  5. Destroyer Weapons of WW2, Friedman, p96
  6. Naval Weapons of WW2, Campbell, p17
  7. Routledge pg 379
  8. Routledge pg 229
  9. Routledge pg 175
  10. Routledge pg 163
  11. Maurice-Jones pg 252
  12. Maurice-Jones pg 256
  13. Routledge pg 77
  14. Hogg pg 106 - 107
  15. "RSL adds key gun mount to collection". Bendigo Advertiser. 20 April 2007. Retrieved 19 November 2011. 
  16. "TS Bendigo". Navy League of Australia - Victoria Division. 29 August 2005. Retrieved 19 November 2011. 


External links

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