QF 3 inch 20 cwt
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| QF 3 inch 20 cwt anti-aircraft gun | |
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 Egyptian gun captured by Israel in the 1956 war. |
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| Type | anti-aircraft gun |
| Place of origin |  United Kingdom |
| Service history | |
| In service | 1914 - 1946[1] |
| Used by | United Kingdom Finland |
| Wars | World War I World War II |
| Production history | |
| Designer | Vickers |
| Specifications | |
| Weight | Gun & breech : 2,250 lb (1,020 kg) Total on 2 wheel platform : 5.99 tons [2] |
| Barrel length | Bore 135 inch (45 cal) Total 140-inch (3,600 mm)[2] |
| Crew | 11[3] |
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| Shell | Fixed QF 12.5 lb (1914); 16 lb HE (1916)[4] |
| Calibre | 3 inch (76 mm) |
| Breech | semi-automatic sliding block[7] |
| Recoil | 11 inches. Hydro spring, constant[2] |
| Carriage | high-angle wheeled, static or lorry mounting |
| Elevation | -10° - 90°[2] |
| Traverse | 360 ° |
| Rate of fire | 16-18 rpm[5] |
| Muzzle velocity | 2500 ft/s (12.5 lb shell) 2000 ft/s (16 lb shell)[6] |
| Effective range | 16,000 ft[5] |
| Maximum range | 22,000 ft (16 lb shell)[5] 23,500 ft (12.5 lb shell)[2] |
The QF 3 inch 20 cwt anti-aircraft gun became the standard anti-aircraft gun used in the home defence of England against German airships and bombers 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, hence the barrel and breech together weighed 2250 lb). While small numbers of other "3 inch" AA guns were used, the 3 inch 20 cwt gun is what writers are usually referring to by "3 inch AA gun".
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[edit] Design and development
The gun was based on a prewar Vickers naval 3-inch (76 mm) QF gun with modifications specified by the War Office in 1914. These (Mk I) included the introduction of a vertical sliding breech-block to allow semi-automatic operation. When the gun recoiled and ran forward after firing, the motion also opened the breech, ejected the empty cartridge and held the breech open ready to reload, with the striker cocked. When the gunner loaded the next round, the block closed and the gun fired.[7]
The early 12.5 lb (5.7 kg) shrapnel shell at 2,500 ft/s (760 m/s) caused excessive barrel wear and was unstable in flight. The 1916 16 lb shell at 2,000 ft/s (610 m/s) proved ballistically superior and was better suited to a high explosive filling.[5]
The Mark I* had different rifling. The Mark II lost the semi-automatic action. The Mk III of 1916 reverted to a 2-motion screw breech to suit available manufacturing capability, and Mk IV had a single-tube barrel and single-motion screw breech;[1] a Welin block with an Asbury breech.[8]
A US Army report on anti-aircraft guns of April 1917 reported that this gun's semi-automatic loading system was discontinued because of difficulties of operation at higher angles of elevation, and replaced by "the standard Vickers-type straight-pull breech mechanism", reducing rate of fire from 22 to 20 rds/minute.[9] Routledge quotes a rate of fire of 16-18 rounds per minute, in the context of the 16 pounder shell of 1916.[5] This would appear to be the effective rate of fire found to be sustainable in action.
Beginning in 1930, a new towed 4-wheeled sprung trailer platform was introduced to replace the obsolete lorries still used as mounts from World War I, together with modern new barrels, and equipment to connect the guns to the new Vickers No. 1 Predictor.[10] 8 more Mks followed between the World Wars.[1] From 1934 the rocking-bar deflection sights were replaced by Magslip receiver dials which received input from the Predictor.[11] Predictor No. 1 was superseded from 1937 by Predictor No. 2, based on a US Sperry AAA Computer M3A3. This was faster and could track targets at 400 mph (640 km/h) at heights of 25,000 ft (7,600 m)[12]
The 3 inch 20 cwt gun was superseded by the QF 3.7 inch AA gun from 1938 onwards but numbers of various Marks remained in service throughout World War II. In Naval use it was being replaced in the 1920s by the QF 4 inch Mk V on HA (high-angle) mounting.
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[edit] Combat use
[edit] World War I
Britain entered World War I with no anti-aircraft artillery. When war broke out and Germany occupied Belgium and North-east France, it was realised that key installations at home could be attacked by air, the government began a search for suitable anti-aircraft guns. The Navy provided the initial 3-inch (76 mm) guns from its warships, approximately 18 by December 1914, for the defence of key installations in Britain, manned by RNVR crews, until the new specialised anti-aircraft version began production and entered service.[13] It was from then onwards operated by Royal Garrison Artillery crews, with drivers and crew for motor lorries provided by the Army Service Corps.
Other earlier anti-aircraft guns based on the existing 13 pounder and 18 pounder guns proved inadequate, apart from the QF 13 pounder 9 cwt but even that could not reach high altitudes and fired a fairly light shell. The 3 inch 20 cwt with its powerful and stable in flight[14] 16 lb (7.3 kg) shell and fairly high altitude was well suited to defending England against high-altitude Zeppelins and bombers. The 16 pound shell took 9.2 seconds to reach 5,000 ft (1,500 m) at 25° from horizontal, 13.7 seconds to reach 10,000 ft (3,000 m) at 40°, 18.8 seconds to reach 15,000 at 55°.[6] This means that the gun team had to calculate where the target would be 9 - 18 seconds ahead, choose the correct fuze setting, load, aim and fire accordingly.
Previous British time-delay fuzes developed for land use had been discovered to be unsuitable for the new vertical shooting, as the gunpowder used in the delay mechanism burned differently and unpredictably at altitude. The new fuze had a modified mechanism and special powder formulation to provide predictable burn speed and hence delay at altitude. Britain lagged behind Germany in switching to clockwork time-delay fuzes. In addition, experience showed that the traditional mechanism in previous time fuzes which detonated the shell on impact even if the time delay failed, had to be disabled, as unexploded AA shells would land amongst those firing them and nearby civilians and hence must not explode on landing.[15]
The carriage's short recoil of 11 inches (280 mm) allowed a higher rate of fire than for AA guns based on long-recoil field guns such as the QF 13 pounder 9 cwt.[16]
By June 1916, 202 3 inch 20 cwt were deployed in the air defence of Britain, of a total of 371 AA guns.[17]
The first guns arrived on the Western Front in November 1916 and by the end of 1916 it equipped 10 sections out of a total of 91.[18] An AA section consisted of 2 guns and became the standard organizational unit.
By the end of World War I, 257 (out of a total of 402 AA guns) were in land service in England on static and lorry mountings, and 102 (out of a total of 348) were in service on the Western Front [19] mounted on heavy lorries, typically the Peerless 4 Ton. In addition, many were mounted on Royal Navy ships.
The following table[6] compares the gun's performance with the other British WWI anti-aircraft guns:-
| Gun | m/v ft/s | Shell (lb) | Time to 5,000 ft (1,500 m) at 25° (seconds) | Time to 10,000 ft (3,000 m) at 40° (seconds) | Time to 15,000 ft (4,600 m) at 55° (seconds) | Max. height (ft)[20] |
| QF 13 pdr 9 cwt | 1990 | 12.5 | 10.1 | 15.5 | 22.1 | 19,000 |
| QF 12 pdr 12 cwt | 2200 | 12.5 | 9.1 | 14.1 | 19.1 | 20,000 |
| QF 3 inch 20 cwt 1914 | 2500 | 12.5 | 8.3 | 12.6 | 16.3 | 23,500 |
| QF 3 inch 20 cwt 1916 | 2000 | 16 | 9.2 | 13.7 | 18.8 | 22,000[21] |
| QF 4 inch Mk V naval gun | 2350 | 31 | 4.4 | 9.6 | 12.3 | 28,750 |
[edit] World War II
At the beginning of World War II in 1939, Britain possessed approximately 500 of these guns, some deployed as light anti-aircraft guns (LAA) for airfield defence until more 40mm Bofors guns arrived, others as heavy anti-aircraft (HAA) guns until numbers of the new 3.7 inch gun arrived.[11] However, it was discovered at mobilization that the 233 guns in HAA reserve were missing various parts and predicted fire instruments.[22] 120 were in France with the British Expeditionary Force in November 1939, compared with 48 of the modern QF 3.7 inch AA gun.[23]
In 1941, 100 of the by-now obsolete guns were converted to become the 3 inch 16 cwt anti-tank gun, firing a 12.5 lb (5.7 kg) armour-piercing shell.[24] They appear to have been mainly deployed in home defence.
[edit] Submarine gun
In World War II the gun was carried by S class, U class and V class submarines.
[edit] Finnish use
Britain supplied 24 Mk 3 guns and 7 M/34 mechanical fire control computers to Finland during the Winter War of 30 November 1939 - March 1940 but they arrived too late to be used. They were used during the Continuation War of 1941 - 1944.[25]
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[edit] Ammunition
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[edit] See also
[edit] Surviving examples
- A gun captured by Israel from Egypt in the 1956 war, missing breech screw, is displayed at the Clandestine Immigration and Naval Museum, Haifa, Israel. See Commons:Category:QF 3 inch 20 cwt for photographs.
- A gun from the Egyptian ship "El Amir Faruk", sunk in 1948, missing the elevation mechanism, is displayed at the Clandestine Immigration and Naval Museum, Haifa, Israel. See Commons:Category:QF 3 inch 20 cwt for photographs.
- Mk 3 gun is displayed at the Ilmatorjuntamuseo, Tuusula Finland
[edit] Notes
- ^ a b c Hogg & Thurston 1972, page 78
- ^ a b c d e Hogg & Thurston 1972, page 79
- ^ Farndale 1988, page 397
- ^ Routledge 1994, page 9, 13
- ^ a b c d e Routledge 1994, page 13
- ^ a b c Routledge 1994, page 9
- ^ a b Routledge 1994, page 12
- ^ http://www.navweaps.com/Weapons/WNBR_3-45_mk1.htm Naval weapons
- ^ Notes on Anti-Aircraft Guns. April 1917, page 22
- ^ Routledge 1994, page 43
- ^ a b Routledge 1994, page 50
- ^ Routledge 1994, page 50-51
- ^ Routledge 1994, page 4-5
- ^ Routledge 1994, page 24
- ^ Hogg & Thurston 1972, page 220
- ^ Hogg & Thurston 1972, page 68
- ^ Farndale 1988, page 397
- ^ Farndale 1986, page 364
- ^ Routledge 1994, page 27. Farndale 1988, page 342 quotes 56 in service in France (meaning Western Front) at the Armistice.
- ^ Hogg & Thurston 1972, Page 234-235
- ^ Routledge 1994, Page 13
- ^ Routledge 1994, page 371
- ^ Routledge 1994, page 125
- ^ Nigel F Evans,BRITISH ARTILLERY IN WORLD WAR 2. ANTI-TANK ARTILLERY
- ^ Jaeger Platoon: Finnish Army 1918 - 1945 Antiaircraft Guns Part 3: Heavy Guns
[edit] References
- General Sir Martin Farndale, History of the Royal Regiment of Artillery. Western Front 1914-18. London: Royal Artillery Institution, 1986
- General Sir Martin Farndale, History of the Royal Regiment of Artillery : Forgotten Fronts and the Home Base 1914-18. London:The Royal Artillery Institution, 1988
- I.V. Hogg & L.F. Thurston, British Artillery Weapons & Ammunition 1914-1918. London: Ian Allan, 1972.
- Brigadier NW Routledge, History of the Royal Regiment of Artillery. Anti-Aircraft Artillery, 1914-55. London: Brassey's, 1994
- Notes on Anti-Aircraft Guns. US Army War College, April 1917. Includes report on 3 inch 20 cwt. Provided online by Combined Arms Research Library
[edit] External links
- British 12-pdr (3"/45 (76.2 cm)) 20cwt QF HA Marks I, II, III and IV
- Ken Musgrave, Diagram of 3 inch 20 cwt gun on Peerless 4 Ton Lorry
