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.

Design
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 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.

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..."

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. 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. 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. 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.

These guns performed well on HMS Prince of Wales (53) 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 (58) and the Town-class cruiser HMS Gloucester (62) 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 (95), 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 (79) 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:
 * King George V-class battleships
 * Dido-class cruisers
 * HMS Vanguard

Land service
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. 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. 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.

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

Specifications

 * 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.
 * 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
 * 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

 * Princess Anne’s Battery remains overlooking the sea at Gibraltar

Notes and references
(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.