| QF 2 pdr Mark VIII ("pom-pom") | |
|---|---|
 Quadruple 2 pdr MK VIII guns on Mk.VII mounting aboardHMASNizam August 1941 | |
| Type | Autocannon |
| Place of origin | United Kingdom |
| Service history | |
| In service | 1917–1940s (Mk II) 1930–1940s (Mk VIII) |
| Used by | British Empire Japan Thailand Russian Empire Kingdom of Italy Netherlands |
| Wars | First World War Second World War |
| 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 HIShiki (Japanese) |
| Specifications (Mk.VIII HV) | |
| Mass | 850 lb (390 kg) |
| Length | 8 ft 6 in (2.59 m) |
| Shell | 40×158mmR |
| Calibre | 40.4 mm (1.59 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)[1] |
| Effective firing range | 3,960 m (13,300 ft) A/A ceiling |
| Maximum firing range | 6,220 m (20,400 ft) at 701 m/s (2,300 ft/s)[1] |
| Feed system | 14-round steel-link belt |
| Filling weight | 71 g (2.5 oz) |
The2-pounder gun, officially theQF 2-pounder (QF denoting "quick firing") and universally known as thepom-pom, was a 40 mm (1.6 in) Britishautocannon, used as ananti-aircraft gun by theRoyal Navy.[note 1] The name came from the sound that the original models make when firing. This QF 2-pounder was not the same gun as theOrdnance QF 2-pounder, used by theBritish Army as ananti-tank gun and atank gun, although they both fired 2 lb (0.91 kg), 40 mm (1.6 in) projectiles.
The first gun to be called a pom-pom was the37 mm Nordenfelt-Maxim or "QF 1-pounder" introduced during theSecond Boer War, the smallest artillery piece of that war. It fired a shell 1 lb (0.45 kg) in weight accurately over a distance of 3,000 yd (1.7 mi; 2.7 km). 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. TheBoers used them against the British, who, seeing their utility, bought guns fromVickers, which had acquiredMaxim-Nordenfelt in 1897.[2][3] During theFirst World War, it was used in the trenches of theWestern 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 43calibres long. This was tested in theArethusa-classlight cruisersHMS Arethusa andUndaunted but did not enter full service, being replaced instead by a larger weapon, the QF 2-pdr Mark II.
TheQF 2-pounder Mark II was a larger version of theQF 1-pounder Maxim gun produced byVickers. It was a 40 mm calibre gun with a water-cooled barrel and a Vickers-Maxim mechanism. It was ordered in 1915 by theRoyal 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 thePierce-Arrow armoured AA lorry. In 1918, one example of this weapon was experimentally mounted on the upper envelope ofHis Majesty's Airship 23r.[4]
Surviving weapons were brought out of storage to see service inWorld War II, mainly on board ships such asnaval trawlers, motor boats and "armed yachts". It was used almost exclusively in the single-barrel, unpowered pedestal mountings P Mark II (Royal Navy nomenclature gave mountings and guns separate Mark numbers) except for a small number of weapons on the mounting Mark XV, which was a twin-barreled, powered mount. These were too heavy to be of any use at sea and were mounted ashore. All were scrapped by 1944.
Some 7,000 guns were made. The gun was also used by the Japanese as the 40 mm/62 "HI" Shiki. TheRegia Marina also used it from the Great War throughout World War II. It was superseded in the 1930s as a primary AA weapon on Italian warships by more modern guns, such as theCannone-Mitragliera da 37/54 (Breda).[6]
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TheRoyal 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 theQF 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 ofcruiser andaircraft carrier size upward.[8][9] From 1935, the quadruple mounting Mark VII, essentially half a Mark V or VI, entered service for ships ofdestroyer andcruiser size. These multiple gun mounts required four guns and were nicknamed the "Chicago Piano".[5] 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 theFlower-class corvettes) and coastal craft (especially earlyFairmile D motor torpedo boats). The Mark XVI mounting was related to the twin mounting Mark V for theOerlikon 20 mm cannon and the "Boffin" mounting for theBofors 40 mm gun. Magazines ranged from 140 rounds per gun for the eight-barrelled mount to 56 rounds for the single mounts.[10] 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*.[10]
The United States Navy also considered adopting the pom-pom gun prior to its entry into the Second World War, and conducted a series of trials between their own1.1" gun, the U.S. Army37 mm Gun, the Vickers 40 mm pom-pom, and theBofors 40 mm:
Among the machine guns under consideration were the Army's 37-mm and the British Navy's 2-pounder, more commonly known as the "pompom." The decision soon narrowed to a choice between the Bofors and the British gun. The British were anxious to have their gun adopted, and the fact that British aid would be readily available in initiating manufacture was put forward as an argument in favor of its selection. The 2-pounder, moreover was giving a good account of itself on British ships. On the other hand, there was the distinct disadvantage that the gun was designed for cordite powder, and no manufacturing facilities for the production of this ammunition were available in the United States. Thorough study revealed that the gun could not be converted to take American powder. Another consideration was muzzle velocity: The pompom had a relatively low velocity, 2350 feet per second as compared with 2830 for the Bofors. The success of the pompom in action was more than offset by the proved qualities of the Bofors in the hands of a number of powers who were using it, and the Bureau decided to join that group. Shortly after the Bureau's selection of the Bofors, British naval officials also decided to adopt the gun.[11]
Although an advanced weapon when it was introduced, by the outbreak of World War II advances in aircraft would have made it obsolete but for the introduction of the high-velocity round and new director designs. It was intended that the curtain of fire it threw up would be sufficient to deter attacking aircraft, which it did, but was hampered by the ineffectiveMk III director.[12] TheMK IV Director with aGyro Rate Unit andType 282 radar[13] was a great advance and was introduced on theKing George V-class battleships. In January 1941,HMS Illustrious′s Mk VIII (HV) mountings performed flawlessly firing 30,000 rounds with very few stoppages.[12] WhenHMS Prince of Wales wasattacked and sunk by Japanese aircraft near Singapore, the subsequent report judged that a single40 mm Bofors gun firing tracer was a more effective anti-aircraft weapon[14][15] than a multiple pom-pom in director control, as the pom-poms did not have tracer ammunition and the pom-pom ammunition had deteriorated badly in its ready use lockers, while the Type 282 radar units also failed in the equatorial heat.[16][17] In the same action, the Commissioned Gunner ofHMS Repulse spent the whole action running from one pom-pom mount to another trying to keep them operational due to the faulty ammunition. The pom-poms onRepulse shot down two of the four confirmed kills made byForce Z,[18] whilePrince of Wales' pom-poms did record hits on enemy aircraft.[19]
The Royal Navy judged the pom-pom's effectiveness to range from about half that of the Bofors, per gun, against torpedo planes to about equal againstKamikaze attackers.[20] It was a ubiquitous weapon that outnumbered the Bofors gun in Commonwealth naval service[21] up to the end of World War II and it shot down many Axis aircraft. Later innovations such as Remote Power Control (RPC) coupled to a radar-equipped tachymetric (speed predicting) director increased the accuracy enormously and problems with the fuses and reliability were also remedied. The single mountings received a reprieve toward the end of the war as the 20 mm Oerlikon guns had insufficientstopping power to counter Japanesekamikaze aircraft and there were insufficient numbers of Bofors guns to meet demand.
TheQF 2-pounder Mark XIV was theRolls-Royce 40 mm cannon, which had been developed byRolls-Royce as a competitor to the40 mm "Vickers S" gun as an aircraft weapon. The latter was the more successful design, and found some use as an anti-tank weapon. A reworked version was adopted by the Royal Navy as a weapon forMotor Gun Boats, being adopted in theFairmile C type as well asBritish Power Boat Company 60- and 70-foot (18- and 21-metre) type MGBs. It had a semi-automatic horizontally slidingbreech block and was shipped on a manually trained pedestal mount. The weapon was not a success and of the 1,200 ordered only some 600 were delivered. It was initially replaced in various MGBs by single 20 mm Oerlikon cannon in order to make good, being ultimately succeeded in the large quick-firer role later in the war by the 57 mmMolins 6-pounder gun, theBritish Army's QF 6-pounder gun anti-tank gun with an auto-loader.
