5.25 inch Gun

5.25 inch Gun

The 5.25 inch Gun was developed in 1942 from the Naval gun. Three, twin mounted guns were handed over to the Army and from these two patterns of single guns were produced. The first, the Mark 1A was purely an Anti-Aircraft gun while the other, the Mark 1B was a dual purpose Anti-Aircraft/Coast Defence gun.
The gun had a loose barel in a short jacket with a horizontal sliding breech block. It had electric firing and air-blast gear. The mountings used a counterbalance weight to balance the muzzle preponderance. The 5.25 inch Gun was completely hydraulic powered. Traversing, elevating, the loading tray and chain rammer, shell supply and fuze setting were all powered. Laying employed remote data transmission to Magslip dials. Open sights were provided for close range aerial targets.


Mark 1Naval pattern, twin mount only
Mark 2Land service design. Simpler breech mechanism & heavier breech ring
Mark 3Land service design using RD Rifling. Trials 1944-46. Cancelled 1948
Mark 4Naval design
Mark 5Land service design. Similar to Mk 2 but automatic air-blast gear
Mark 5/1As for Mk 5 but slight dimensional changes
All subsequent Marks for Naval service


Mark 1ALand service, Anti-Aircraft only. Open back mild steel shield
Mark 1BLand service, dual Anti-Aircraft/Coast Defence. Enclosed armoured turret.
Powered shell hoist, fans & louvres for forced ventilation. Semi-auto sights
for seaward firing
Mark 2ANaval twin mounting


5.25 inch QF Gun Mk 2, on Mounting Mk 1A or 1B

Weight of Gun & Breech Mechanism9,587 lbs
Total length275.5 inches
Length of bore262.5 inches (50 calibres)
Rifling36 grooves, uniform Right Hand 1/30
Breech MechanismHorizontal sliding block, semi-automatic,
percussion fired
Elevation0º to +70º
Weight in action30 tons 6 cwt – Mk 1A
49 tons 10 cwt – Mk1B
Rate of Fire8 rounds per minute


Firing standard 80 lbs Shell, HE

Muzzle Velocity2,800 feet per second
Maximum horizontal range27,000 yards
Maximum ceiling55,600 feet
Effective ceiling (with Predictor No.10 & Fuze 208)43,000 feet


Shell, HE Mark 3CSquare base shell weighing 79 lb 15 oz. Fuze Time 208
Shell, Semi-Armour Piercing Mark 2CPiercing shell with ballistic cap. Weight 79 lb 15 oz fitted with base percussion Fuze 501 or 502. Seaward firing only
Propelling ChargeSeperate loading brass cased charge (full & reduced)
The Royal Artillery 1939-45