QF 2 pounder naval gun

QF 2 pdr Mark VIII ("pom-pom")
Quadruple 2 pdr MK VIII guns on Mk.VII mounting aboard HMAS Nizam August 1941
Type
Place of origin	United Kingdom
Service history
In service	1915–1940s (Mk II) 1930–1940s (Mk VIII)
Used by	British Empire Japan Russian Empire Kingdom of Italy
Wars	World War I World War II
Production history
Designer	Vickers Armstrongs
Designed	1915 (Mk II) 1923 (Mk VIII)
Variants	Low-velocity (LV) & high-velocity (HV), RHI, LHI, RHO, LHO for multiple mountings, Type 91 HI Shiki (Japanese)
Specifications (Mk.VIII HV)
Weight	850 lb (390 kg)
Length	8 ft 6 in (2.59 m)
Shell	40×158mmR
Calibre	40-millimetre (1.6 in)
Barrels	1, 4 or 8
Rate of fire	115 rpm
Muzzle velocity	new gun: 732 m/s (2,400 ft/s) worn gun: 701 m/s (2,300 ft/s)
Effective firing range	3,960 m (13,300 ft) A/A ceiling
Maximum firing range	6,220 m (6,800 yd) at 701 m/s (2,300 ft/s)
Feed system	14-round steel-link belt
Filling weight	71 g (2.5 oz)

The 2-pounder gun, officially designated the QF 2-pounder (QF denoting "quick firing") and universally known as the pom-pom, was a 40-millimetre (1.6 in) British , used as an anti-aircraft gun by the Royal Navy. The name came from the sound that the original models make when firing. This QF 2-pounder was not the same gun as the Ordnance QF 2 pounder, used by the British Army as an anti-tank gun and a tank gun; they shared only the projectile weight of 2 pounds.

The first gun to be called a pom-pom was the 37 mm Nordenfelt-Maxim or "QF 1-pounder" introduced during the Second Boer War, the smallest artillery piece of that war. It fired a shell one pound in weight accurately over a distance of 3,000 yd (2,700 m). The barrel was water-cooled, and the shells were belt-fed from a 25-round fabric belt. The Boers used them against the British, who, seeing their utility, had the design copied by Vickers, who were already producing Maxim guns.

During the First World War, it was used in the trenches of the Western Front against aircraft.

The first naval pom-pom was the QF 1.5-pdr Mark I, a piece with a calibre of 37 mm (1.46 in) and a barrel 43 calibres long. This was trialed in the Arethusa-class light cruisers HMS Arethusa and Undaunted, but did not enter full service, being replaced instead by a larger weapon, the QF 2-pdr Mark II (see below).