QF 3-inch 20 cwt

QF 3 inch 20 cwt anti-aircraft gun
Aboard HMS Royal Oak in World War I
Type	Anti-aircraft gun
Place of origin	United Kingdom
Service history
In service	1914–1947[1]
Used by	United Kingdom Australia Canada Finland Ireland
Wars	World War I World War II
Production history
Designer	Vickers
Variants	Mk I, Mk I*, Mk IB, Mk 1C, Mk 1C*, Mk IE, Mk SIE, Mk II, Mk III, Mk IV, Mk IVA[2]
Specifications
Mass	2,240 lb (1,020 kg), gun and breech 5.99 tons,[3] with 2-wheel platform
Barrel length	Bore: 11 ft 4 in (3.45 m) (45 cal) Total: 11 ft 9 in (3.58 m)[3]
Crew	11[4]
Shell	Fixed QF HE 76.2 × 420 mm R[5][6]
Shell weight	12.5 lb (5.7 kg), 1914; 16 lb (7.3 kg), 1916
Calibre	3 inches (76 mm)
Breech	Semi-automatic sliding-block[7]
Recoil	11 inches (280 mm). hydro spring, constant[3]
Carriage	High-angle wheeled, static, or lorry mounting
Elevation	−10 – 90°[3]
Traverse	360°
Rate of fire	16–18 rpm[8]
Muzzle velocity	2,500 ft/s (760 m/s), 12.5 lb (5.7 kg) shell 2,000 ft/s (610 m/s), 16 lb (7.3 kg) shell[9]
Effective firing range	16,000 ft (4,900 m)[8]
Maximum firing range	23,500 ft (7,200 m), 12.5 lb shell[3] 22,000 ft (6,700 m), 16 lb shell[8]

The QF 3-inch 20 cwt anti-aircraft gun became the standard anti-aircraft gun used in the home defence of the United Kingdom against German Zeppelins airships and bombers and on the Western Front in World War I. It was also common on British warships in World War I and submarines in World War II. 20 cwt referred to the weight of the barrel and breech, to differentiate it from other 3-inch guns (1 cwt = 1 hundredweight = 112 lb, 51 kg, hence the barrel and breech together weighed 2,240 lb, 1,020 kg). While other AA guns also had a bore of 3 inches (76 mm), the term 3-inch was only ever used to identify this gun in the World War I era, and hence this is what writers are usually referring to by 3-inch AA gun.