Royal Canadian Navy QF 2-pounder pom-pom AA Gun

QF 2-pounder pom-pom anti-aircraft gun, RCN‍

(Library and Archives Canada Photo, MIKAN No. 3566440)

QF 2-pounder AA Gun being fired on HMCS Assiniboine, 10 July 1940.

(Library and Archives Canada Photo, MIKAN No. 3566993)

RCN QF 2-pounder pom-pom anti-aircraft gun, Vickers, Sons & Maxim LL Machine Gun Mk. I weight (410 lbs), VSM 1905 manned on the RCN destroyer HMCS Assiniboine, 1940.

(Library and Archives Canada Photo, MIKAN No. 3566434)

QF 2-pounder pom-pom Mk. VIII, V.S.M. (Vickers, Sons & Maxim LL) Automatic Gun being manned on HMCS Assiniboine, 10 July 1940.

(Library and Archives Canada Photo, MIKAN No. 3196183)

Workmen assemble quad 40-mm (2-pounder) naval guns in the Dominion Engineering Works plant, 1942.

The QF 2-pounder (QF denoting "quick firing") and universally known as the pom-pom, was a 40-millimetre (1.6 in) British autocannon, used as an anti-aircraft gun by the Royal Navy. The name came from the sound that the original models make when firing. The QF 2-pounder Mark II was essentially a scaled-up version of the QF 1 pounder Maxim gun produced by Vickers. It was a 40 mm calibre gun with a water-cooled barrel and a Vickers-Maxim mechanism. It was ordered in 1915 by the Royal Navy as an anti-aircraft weapon for ships of cruiser size and below. The original models fired from hand-loaded fabric belts, although these were later replaced by steel-link belts. This "scaling-up" process was not entirely successful, as it left the mechanism rather light and prone to faults such as rounds falling out of the belts.

The Royal Navy had identified the need for a rapid-firing, multi-barrelled close-range anti-aircraft weapon at an early stage. Design work for such a weapon began in 1923 based on the earlier Mark II, undoubtedly to use the enormous stocks of 2-pounder ammunition left over from the First World War. Lack of funding led to a convoluted and drawn-out design and trials history and it was not until 1930 that these weapons began to enter service. Known as the QF 2-pounder Mark VIII, it is usually referred to as the "multiple pom-pom".

The initial mounting was the 11.8 to 17.35 ton, eight-barrelled mounting Mark V (later Mark VI), suitable for ships of cruiser and aircraft carrier size upward. From 1935, the quadruple mounting Mark VII, essentially half a Mark V or VI, entered service for ships of destroyer and cruiser size. These multiple gun mounts required four guns and were nicknamed the "Chicago Piano".[6] The mount had two rows each of two or four guns. Guns were produced in both right- and left-hand and "inner" and "outer" so that the feed and ejector mechanisms matched.

Single-barrelled mounts, the Mark VIII (manual) and Mark XVI (power operated), were also widely used, mainly in small escorts (such as the Flower-class corvettes) and coastal craft (especially early Fairmile D motor torpedo boats). The Mark XVI mounting was related to the twin mounting Mark V for the Oerlikon 20 mm cannon and the "Boffin" mounting for the Bofors 40 mm gun. Magazines ranged from 140 rounds per gun for the eight-barrelled mount to 56 rounds for the single mounts. This large ammunition capacity (1,120 rounds) gave the eight-barrelled mount the ability to fire continuously for 73 seconds without reloading. A high velocity (HV), 1.8 lb (820 g), round was developed for the pom-pom, just before the Second World War, which raised the new gun muzzle velocity from 2,040 ft/s (622 m/s) to 2400 ft/s (732 m/s).

Many older mountings were modified with conversion kits to fire HV ammunition, while most new mounts were factory built to fire HV ammunition. A mount modified or designed for HV ammunition was given a '*' designation; for example a Mk V mount modified for HV ammunition would be a Mk V*. (Wikipedia)

(Library and Archives Canada Photo, MIKAN No. 39290670

Overhead view of a quad 2-pounder and its ship's crew.

(JustSomePics Photo)

QF 2-pounder Mk. VIII single mount from HMCS Kamloops, displayed in Canadian War Museum, Ottawa, Ontario.