QF 5.25 inch gun

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, 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.

Country Name Origin Year
United Kingdom - UK (Great Britain) 1940
Country Name Operational Year Retirement Year
United Kingdom - UK (Great Britain) 1940 1966 View

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 purpose weapon.

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.

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...

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. 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 a World War II AA engagement. The dual-mount turret could traverse at 10 deg/s, which was too slow to track quickly enough to engage at close ranges the higher-speed aircraft of the Second World War. The elevation and traverse rates were still higher than some other contemporary weapons, such as the 4.1-inch C/31 and C/37 twin mounts carried on the Bismarck and Tirpitz.

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. 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. HMS Spartan, a Bellona-class cruiser, was sunk at anchor in 1944 by a Luftwaffe guided missile.

The gun had a maximum surface range of 24,070 yards, 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.

Type Dual-purpose gun
Place of origin United Kingdom
Service history
In service 1940-1966 (naval)
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
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)
Army AA: 2,800 ft/s (850 m/s)
Effective firing 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)
Maximum firing 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)

End notes