QF 12-pounder 18 cwt naval gun

Ordnance QF 12 pounder 18 cwt
Deployed as anti-aircraft gun on HMS Agamemnon off Salonika, 1916
Type	Naval gun, Coastal defence
Place of origin	United Kingdom
Service history
In service	1906–1921?
Used by	Royal Navy
Wars	World War I
Production history
Designer	Elswick Ordnance Company
Designed	189?
Specifications
Weight	Gun & breech: 2,016 lb (914 kg)
Barrel length	Bore: 150 inch (3.81 m) (50 calibres)
Shell	Separate QF 12.5 lb (5.66 kg)
Calibre	3 in (76 mm)
Rate of fire	20 rd/min
Muzzle velocity	2,600 ft/s (790 m/s)
Effective firing range	9,300 yards @ +20° (8,500 m @ +20°)

The QF 12 pounder 18 cwt gun was a 3 inch high-velocity naval gun used to equip larger British warships such as battleships for defence against torpedo boats. 18 cwt referred to the weight of gun and breech (18 × 112 lb = 2,016 lb or 914 kg), to differentiate the gun from others that also fired the "12 pound" (actually 12.5 lb or 5.7 kg) shell.

Guns were mounted in:

The gun was superseded in the anti-torpedo boat role on new capital ships from 1909 onwards by the far more powerful BL 4-inch Mk VII gun.

In World War I four guns were landed for service in the East Africa campaign, on 10 February 1916, and were used until September. They constituted the 9th Field Battery manned by Royal Marines. They were originally towed by oxen and later by Napier lorries.

Fourteen of these guns were mounted in coast defence batteries in the 'Middle Line' of the defences of the Firth of Forth when it was established in 1915 (the batteries on Inchcolm (8 guns), Inchmickery (4) and Cramond Island (2). During the general revision of the defences in 1916/17 two of the guns were removed to store, four moved to other batteries (Hound Point and Downing Point). The document setting out the armaments of the Forth differentiate clearly between the 12cwt and 18cwt types, both of which were in use in the fortress.

The gun fired the same 12.5 lb 3-inch (76 mm) shells as the other British "QF 12 pounder" guns, but used its own larger separate cartridge case to accommodate a larger quantity of cordite propellant.