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QF 5.25 inch Mark I
HMS Sirius guns.jpg
5.25 in dual turret on HMS Sirius. A large number of empty cartridge cases stand on the deck in foreground, fired in support of the Allied invasion of Normandy, June 1944
Type Dual-purpose gun
Place of origin United Kingdom
Service history
In service 1940-1966 (naval)[1]
1942-1960s (land)
Used by Royal Navy
Royal Artillery
Royal Australian Artillery
Wars World War II
Korean War
Production history
Designed 1935
Variants Mk I, Mk II[2]
Specifications (bore length)
Weight Barrel & breech: 9,616 lb (4,362 kg)
Length Total: 22 ft 11.5 in (7 m)
Barrel length Bore: 21 ft 10.5 in (6.67 m) L/50 (cal)

Shell Separate QF, 80 pounds (36.29 kg) SAP or HE
Calibre 5.25-inch (133 mm)
Elevation -5 to +70 degrees
Rate of fire 7-8 rpm sustained fire
Muzzle velocity Naval: 2,672 ft/s (814 m/s)
[3] Army AA: 2,800 ft/s (850 m/s)[4]
Effective range Naval: 23,400 yd (21,400 m) at 45 degrees with HE shell at 2,600 ft/s (790 m/s)
AA: 36,000 ft (11,000 m)[4]
Maximum range Naval: 24,070 yd (22,010 m) at 45 degrees with HE shell at 2,672 ft/s (814 m/s)
AA: 46,500 ft (14,200 m)[3]

The QF 5.25 inch Mark I gun was the heaviest dual-purpose gun used by the Royal Navy. Although it was a less than completely successful design,[5] it saw extensive service during the Second World War. A slightly more powerful Mk II variant was also deployed by the British Army as an anti-aircraft and coast-defence gun.


QF 5.25 inch Mark I turret on HMS King George V

Unlike the equivalent French design of 138 mm guns used on the Mogador-class destroyers, the QF (quick-firing) 5.25 inch was designed to be a dual-purpose naval gun, for use against both ships and aircraft. Combining the secondaries and heavy anti-aircraft armament would allow a significant savings of weight for the King George V class of battleships, which were originally intended to meet the Washington Naval Treaty limit of 35,000 tons. The gun fired an 80 lb (36 kg) shell, considered the largest that a gun crew could handle easily enough to give the rate of fire needed for anti-aircraft use. The ballistic performances were very good, as the maximum range was in excess of 21,000 metres and the AP projectile could penetrate 3 in (76 mm) at around 9,500 metres. This compared well with the closest Italian design, the 135/45 mm, that was inferior almost in anything as power (range 19,600 metres with a 32.7 kg shell, 6 rounds per minute), and most important, it was not originally meant as dual purpuse weapon.[6]

A class of anti-aircraft cruisers, the Dido class, was also designed using the gun as the main armament. 267 guns were built, making it the most numerous and important gun in the RN's dual purpose gun inventory. Not enough were available when the first Didos were launched for the full complement of ten guns; priority was given to the battleships. The Bellona-class cruisers, a modification of the design of the Dido class, used a highly modified RP10Mk2 mount with Remote Power Control and much improved training and elevating speeds. The number of turrets was reduced from five to four, and the light AA numbers were increased.

Naval service

The RN Gunnery Pocket Book published in 1945 states:

These guns are combined High Angle and Low Angle Guns. The Mark II Mounting is found in all Dido class cruisers. The Mark I Mounting is found in King George V class battleships, where they fulfil the combined functions of H.A. Long Range Armament and Secondary Armament against surface craft. The main differences between the two mountings lie in the arrangements of the shellrooms and magazines, and the supply of ammunition to the guns. In this chapter, only the Mark II Mounting, as found in Dido class cruisers, is discussed. The 5.25 in. calibre with separate ammunition is used for dual High Angle and Low Angle Armament, since it gives the reasonable maximum weight of shell which can be loaded by the average gun's crew for sustained periods at all angles of elevation. The maximum rate of fire should be 10-12 rounds per minute.[7][8]

A wartime account describes HMS Euryalus firing her 5.25 in guns:

We left Suez and headed for the Gulf, where at 1PM the ship's company closed to action-stations and gave a demonstration of the cruiser's fire power to the army officers. Fire was opened with the 10 5.25" guns in the form of a low angle barrage accompanied by fire from smaller guns. Set to burst at 2000 yds range, a terrific barrage was put up for two minutes and we fired some two hundred rounds of 5.25-inch HE...A wall of bursting shell was thrown up just above sea level and I could see that the army officers were impressed...[9]

Unfortunately, the gunhouse was cramped, and the heavy projectile and cartridge cases resulted in a reduced sustained rate of fire from the designed twelve rounds per minute to seven or eight according to postwar publications.[10][11][12] However, this does not appear to have reduced HMS Euryalus's rate of fire, at least over a one-minute period, which would be the typical time for an World War II AA engagement.[13] The dual-mount turret could traverse at 10 deg/s which was too slow to track quickly enough to engage the higher-speed aircraft of the Second World War, at close ranges.[11][14] The elevation and traverse rates were still higher than some other contemporary weapons, such as the 4.1" C/31 and C/37 twin mounts carried on the Bismarck and Tirpitz.[15]

These guns performed well on HMS Prince of Wales during Operation Halberd but Prince of Wales was overwhelmed in the loss of Force Z, due to factors unrelated to the 5.25 inch weapon system.[16] No Dido-class cruisers were lost in the Battle of Crete, although the Crown Colony-class cruiser HMS Fiji and the Town-class cruiser HMS Gloucester were both bombed and sunk, after they ran out of AA ammunition. No Dido-class cruiser was lost from air attack, although four were sunk by submarine or surface-launched torpedoes.[17] HMS Spartan, a Bellona-class cruiser, was sunk at anchor in 1944 by a Luftwaffe guided missile.[17]

The gun had a maximum surface range of 24,070 yards,[3] and the 80-pound shell was well-suited for use against destroyers and small cruisers. However, the gun was used on several occasions against heavier ships, most notably against the German battleship Bismarck.

In 1944, VT-fuzed (using radar to detect proximity to a target) shells for the gun became available, making the gun significantly more effective against aircraft.

The RP10 mounting was improved and the fire control upgraded for the installation on the Bellona-class cruisers, and the battleships HMS Anson and HMS Vanguard, the latter of which would prove to be the last battleship ever built for the Royal Navy. However, Vanguard never saw action.

Ship classes

Ships with QF 5.25 inch Mark I guns:

Land service

Twin naval anti-aircraft mounting at Primrose Hill, London, August 1943

A preserved 5.25-in gun at Princess Anne's Battery, Gibraltar, the only intact battery of 5.25 inch AA guns anywhere in the world

In early 1942 the Governor of Gibraltar sought 5.25-in guns for dual anti-aircraft/coast defence role. None were forthcoming. However, later that year AA Command in UK acquired three twin-gun turrets from the Admiralty, these were installed around London in permanent positions. Trials and use led the army to design a single gun mounting in two marks, both with an underground engine room to provide electrical and hydraulic power for traverse, elevation, fuze setting, ramming and other tasks. Fitted with the standard army Machine Fuze Setter No 10 these guns had a rate of fire of 10 rds/min and a maximum height of 50,000 ft, with an effective height of 36,000 ft.[18] Mark 1A was a mild steel turret for AA use only, Mk 1B was an armoured turret for AA/CD use. The gun was designated Mk 2.

By the end of 1943 only 16 of the new guns had been installed, far below projections. By the end of the war 164 guns had been produced.[19] The HE shells were fuzed with the standard army No 208 mechanical time fuze, used with 3.7 and 4.5-inch AA guns. The guns remained in service after World War II and in 1953 11 guns were installed in Gibraltar.[20][21]

Late in World War II 7 guns were mounted in Australia and 3 in New Guinea in enclosed single-gun AA/CD turrets.[22]


  • Bore Diameter: 5.25 inches (133 mm)
  • Barrel Length: 6.668 m (50 calibres)
  • Shell weight: 80 lbs (36.3 kg)
  • Range: 24,070 yds (22,000 m) at 45 degrees
  • Anti Aircraft Ceiling: 46,500 ft (14,170 m)
  • Rate of Fire: Sustained 7-8 rpm, 18 RPM claimed for HMS Vanguard.[23]
  • Penetration: side armour: 3 inches (76 mm) 9,500 yards (8,690 m) or 11,900 m, depending on the sources; the gun was not capable to penetrating 2 inches (51 mm) of deck armour at any range[24]
  • Mounting weight: 78.7 metric tons (varied)
  • Mounting elevation: -5 to +70 degrees
  • Training/Elevating speeds: 10/10 degree/second and 20/20 in RP10 mounts.


Surviving examples

See also

Notes and references

  1. HMNZS Royalist was not decommissioned until 1966, although she appears to have ended "active service" some years before. All other ships were decommissioned by 1962.
  2. Mk I = Mark 1, Mk II = Mark 2. Britain used Roman numerals to denote "Marks" (i.e. models) of ordnance until after World War 2. Hence this article covers the 2 models of QF 5.25 inch gun.
  3. 3.0 3.1 3.2 Campbell, Naval Weapons of WW2, p44
  4. 4.0 4.1 Routledge 1994, page 87
  5. Page of Navweapons
  6. Navweapons site, italian Mod.1938
  7. The Gunnery Pocket Book. 1945. p. 51. 
  8. Sired, Enemy Engaged, p23, states: "The Italians did not press home their attacks very hard and I thought they had a lot to put up with, as each (10 5.25 in gun) cruiser could fire 100 rounds of 5.25" HE shell per minute..." Ronald Sired was a gunnery petty officer on board HMS Euryalus. The accuracy of Sired's account was praised by Captain FC Flynn RN. Official Historian of the Naval Campaigns in the Mediterranean
  9. Sired, Enemy Engaged, p63.
  10. Williams, Anthony G. "Medium Calibre guns of the Royal Navy in World War II". 
  11. 11.0 11.1 "Britain 5.25"/50 (13.4 cm) QF Mark I". 
  12. Garzke&Dullin, 1980. pp. 228-229
  13. Hodges, Tribal Class Destroyers, p32: Diagram of High Level Bomber Attack: A 240mph target, at 12 thousand feet altitude could expect to be under for fire about 75 seconds, from the time it enters the effective range of the HACS until it flies to within the minimum range of a 5.25 gun elevated to 70 degrees. A Tribal-class destroyer would be able to engage the same target for about 37 seconds.
  14. A 270 knot (500 km/h) target crossing the line of sight at right angles, at 2000 yards (1829 m) range, will move across the line of sight at 4.5 degrees per second. This simple fact of geometry appears to contradict the assertion that a 10-degree-per-second traverse rate was too slow to track a high-speed aircraft.
  15. Navweaps 10.5 cm/65 (4.1") SK C/33
  16. Battleship, Middlebrook
  17. 17.0 17.1 Raven, Dido Class Cruisers
  18. Routledge 1994, page 87, 78. "Effective height" was the greatest at which a 400 mph target could be engaged for 30 seconds using Predictor No. 10 (the all-electric US Bell AAA Computer) : hence with a realistic prospect of damaging the target. The shell could travel up to 50,000 ft but with little tracking capability hence little effectiveness.
  19. Routledge 1994, page 92
  20. Hogg pg. 105-106
  21. Routledge pg 77, 92,204, 207, 432
  22. DW Spethman, "The garrison guns of Australia 1788-1962", pages 145-6. Published by Ron H Mortensen, Inala Qld, 2008. ISBN 978-0-9775990-8-0
  23. Garzke, p291: " The guns were fully automatic and remotely controlled, with a rate of fire of eighteen rounds per minute."
  24. Naval Weapons page gives 3 inches at 9,500 yards

(1)The last 5.25 Dido was HMNZS Royalist which operated with the RN during the Indonesian Confrontation in 1965. It was withdrawn after boiler contamination in Nov 65. The Pakistan Navy, Babur (HMS Diadem) became a training ship in 1962. The last of the others to operate,were Black Prince in 1955 and HMS Eyularus in 1954 South Atlantic squadron.


  • Brown, D.K.Nelson to Vanguard: Warship Design and Development 1923-1945
  • Campbell, John, British Naval Guns 1880-1945 No 14" article in "Warship Volume VIII
  • DiGiulian, Tony, Nav Weaps page
  • Garzke, William H., Jr.; Dulin, Robert O., Jr. (1980). British, Soviet, French, and Dutch Battleships of World War II. London: Jane's. ISBN 0-7106-0078-X.
  • Hogg, Ian V. 1998. Allied Artillery of World War Two. The Crowood Press: London. ISBN 1-86126-165-9
  • Horner, David, The Gunners - A History of Australian Artillery. Allen & Unwin: St Leonards. ISBN 1-86373-917-3
  • Ireland, Bernard, Jane's Battleships of the 20th Century
  • The Gunnery Pocket Book
  • Routledge, Brigadier NW. 1994. History of the Royal Regiment of Artillery - Anti-Aircraft Artillery 1914-55. Brassey's: London. ISBN 1-85753-099-3
  • Sired, Ronald ; edited by Flynn, F.C. 1957 Enemy engaged : a naval rating with the Mediterranean fleet, 1942-44 W. Kimber: London.

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