The 2-pounder gun, officially the QF 2-pounder (QF denoting "quick firing") and universally known as the pom-pom, was a 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. 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, although they both fired , projectiles. Predecessors - Boer War and the Great War QF 1 pounder 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 in weight accurately over a distance of . The barrel was water-cooled, and the shells were belt-fed from a 25-round fabric belt. This "auto cannon" fired explosive rounds (smokeless ammunition) at 450 rounds per minute. The Boers used them against the British, who, seeing their utility, bought guns from Vickers, which had acquired Maxim-Nordenfelt in 1897. During the First World War, it was used in the trenches of the Western Front against aircraft. QF 1½ pounder The first naval pom-pom was the QF 1.5-pdr Mark I, a piece with a calibre of and a barrel 43 calibres long. This was tested in the Arethusa-class light cruisers and but did not enter full service, being replaced instead by a larger weapon, the QF 2-pdr Mark II (see below). QF 2-pounder Mark II The QF 2-pounder Mark II was a larger 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. The enlargement was not entirely successful, as it left the mechanism rather light and prone to faults such as rounds falling out of the belts. In 1915, sixteen 2-pounders were mounted in armoured lorries as the Pierce-Arrow armoured AA lorry. In 1918, one example of this weapon was experimentally mounted on the upper envelope of His Majesty's Airship 23r. Surviving weapons were brought out of storage to see service in World War II, mainly on board ships such as naval trawlers,