4.5 inch Anti-Aircraft Gun

4.5 inch Anti-Aircraft Gun

The 4.5 inch Anti-Aircraft Gun was a Naval gun, adopted for the army in place of a 4.7 inch gun that was being developed in the 1920’3 and early 30’s. Because, in 1937, priority was given to the 3.7 inch gun there was little chance of getting the 4.7 inch into production. The 4.5 inch on the other hand was already in production, the ballistics were close to the projected 4.7 inch and as most of the places the army intended deploying the guns were near Naval installations, ammunition supply through the Navy was assured. The gun was therefore approved for land service in 1938 as the 4.5 inch gun Mark 2.

The gun had a loose liner and short jacket with a horizontal, sliding breech block. the mounting was static although it could be moved on a special Transporting Limber. The rear trunnioned gun was balanced by a heavy counterbalance on a cantilever arm at the rear. An electric rammer was fitted in 1940 giving a rate of fire of 8 rounds per minute. The mounting was fitted with an open back, mild steel shield.

In 1940-41 some guns were used in a dual Anti-Aircraft/Coast Defence role sited near the coast. They were supplied with a semi-armour piercing shell for usr against targets at sea. Other than those guns, ground targets were only ever to be engaged in a dire emergency.

The 4.5 inch Anti-Aircraft Gun was mostly superseded by the 5.25 inch gun in 1944-45. It was only declared obsolete in 1951. There was no variant models of the gun, all other variants being Naval guns. There were two variants of the mounting, the second being the Mark 1A allowing more depression for coastal mounted guns.


4.5 inch Gun Mark 2 on Mounting Mark 1

Weight of Gun & Breech Mechanism6,180 lbs
211.75 inches211.75 inches
Length of bore200.25 inches (45 calibres)
Rifling12 grooves, uniform Right Hand 1/25
Breech MechanismHorizontal sliding block, semi-automatic,
percussion fired
Elevation0º to +80º (Mk 1A – -9½º to +80º)
Weight in action14.75 tons
Rate of Fire8 rounds per minute


Firing standard 54 lb HE Shell

Muzzle Velocity2,400 feet per second
Maximum horizontal range22,800 yards
Maximum ceiling44,000 feet
Effective ceiling (with Predictor No.10 & Fuze 208)34,500 feet


Fixed, case charge

Shell, HE Mark 1CSquare base, taper nose shell weighing 54 lb 7 oz. Fuze Time 207 or 209 (later 208)
Shell, Semi-Armour Piercing Mark 4CPiercing shell with ballistic cap. Weight 55 lb fitted with base percussion Fuze 501 or 502
Shell, S-AP/NT Mark 2 or 3Naval shell for dual role guns. NT (night tracer) fitted below base fuze
Shell, Shrapnel Mark 2CFor defence against close flying aircraft. Containing 693 bullets & fitted with Time Fuze 199
Propelling ChargeNaval shell for dual role guns. NT (night tracer) fitted below
base fuze
The Royal Artillery 1939-45