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The 40mm L/56 machine gun was originally produced by Bofors, a Swedish company. The US Army first showed interest in this gun in 1937, but the Navy received some to mount on submarines and destroyers. In 1940, a twin barrelled version arrived from Sweden, and the York Lock & Safe Co. began to manufacture them for the Navy. (A formal liscense was not acquired until June 1941.) In January 1942, the first twin mount rolled off the line, following by a quadruple mount three months later. The quad was mounted in the Wyoming, a gunnery training ship. In July, the first twin was mounted on the destroyer Coghlan, and then continued to be installed throughout the exsisting Navy ships until mid-1944, when the demand was finally satisfied. The extreme accuracy of this gun, when it was paired with the Mark 51 director, proved to be devastating to aircraft, with the exception of kamikaze attacks during 1945. Although the gun could hurl 160 shells per minute into the air, it could not handle the VT proximity fuse. This shortfall would lead the development of the 76mm AA gun, but those guns did not make their debut before the end of World War II. Overall though, the 40mm Bofors proved to be a vital AA gun throughout WWII, and was a drastic improvement over the 1.1" AA gun. |
| Gun Characteristics | |
| Designation | 4 cm/56 (1.57") Mark 1 and Mark 2 |
| Ship Class Used On | Almost all |
| Date Of Design | 1941 |
| Date In Service | 1942 |
| Gun Weight | about 1,150 lbs. (522 kg) |
| Gun Length oa | 98.4 in (2.499 m) (overall) |
| Bore Length | 88.6 in (2.250 m) |
| Number Of Grooves | 16 |
| Length Of Rifling | USA: 75.85 in (1.927 m) German: 76.06 in (1.932 m) |
| Chamber Volume | 28.3 in3 (0.464 dm3) |
| Rate Of Fire | 120 rounds per minute per barrel nominal 140-160 rounds per minute when horizontal (gravity assist) |
| Ammunition | |
| Type | Fixed |
| Weight of Complete Round | USA - 4.75 lbs. (2.15 kg) UK - 4.88 lbs. (2.21 kg) Others - N/A |
| Projectile Types and Weights | USA HE - 1.985 lbs. (0.900 kg) AP - 1.960 lbs. (0.899 kg)
UK
Germany
Japan |
| Bursting Charge | USA - 3.39 oz. (96 g) |
| Overall Length | USA - 17.62 in (44.75 cm) UK - 17.75 in (45.1 cm) Others - N/A |
| Propellant Charge | USA - 0.694 lbs. (0.314 kg) NC 025 UK - 0.719 lbs. (0.326 kg) FNH/PO22 Germany - 0.668 lbs. (0.303 kg) Str PC/38N Japan - 0.661 lbs. (0.3 kg) |
| Muzzle Velocity | USA Marks 1 and 2: 2,890 fps (881 mps) UK Mark NI: 2,720 fps (829 mps) Germany Flak 28: 2,801 fps (854 mps) Japanese Type 5: 2,953 fps (900 mps) |
| Working Pressure | USA - 19.5 tons/in2 (3,070 kg/cm2) UK - 19.68 tons/in2 (3,100 kg/cm2) Others - N/A |
Approximate Barrel Life | USA - 9,500 Rounds UK - 10,000 Rounds Germany - 10,000 Rounds |
| Magazine capacity per gun | HMS Vanguard: 1,269 rounds (including 34 practice) Others: N/A |
| Range (USA) | ||
| Elevation | With 1.985 lbs. (0.900 kg) HE Mark 2 Shell | With 1.960 lbs. (0.899 kg) AP M81A1 Shell |
| Range @ 10 degrees | 6,844 yards (6,258 m) | 6,466 yards (5,913 m) |
| Range @ 15 degrees | 8,227 yards (7,523 m) | 7,580 yards (6,931 m) |
| Range @ 20 degrees | 9,295 yards (8,499 m) | 8,389 yards (7,671 m) |
| Range @ 25 degrees | 10,103 yards (9,238 m) | 8,959 yards (8,192 m) |
| Range @ 30 degrees | 10,691 yards (9,776 m) | 9,358 yards (9,358 m) |
| Range @ 35 degrees | 11,057 yards (10,111 m) | 9,568 yards (8,749 m) |
| Range @ 40 degrees | 11,208 yards (10,249 m) | 9,618 yards (8,795 m) |
| Range @ 45 degrees | 11,133 yards (10,180 m) | 9,492 yards (9.679 m) |
| AA Ceiling | 22,299 feet (6,797 m) | N/A |
| Note: Most USA produced ammunition was set to detonate at 4,000-5,000 yards (3,700-4,570 m) so as to minimize damage due to "friendly fire." | ||
| Range (UK) | |
| Elevation Muzzle velocity of 2,800 fps (853 mps) | With 1.97 lbs. (0.894 kg) HE Shell |
| Range @ 45 degrees | 10,750 yards (9,830 m) |
| AA Ceiling | 23,500 feet (7,160 m) |
| Note: British rounds self-destructed at 3,000-3,500 yards (2,700-3,200 m) but this could be increased to 7,000 yards (6,400 m) in some ammunition types. | |
| Range (Germany) | |
| Elevation Muzzle velocity of 2,800 fps (853 mps) | With 2.105 lbs. (0.955 kg) HE Shell |
| Range @ 45 degrees | about 10,500 yards (9,600 m) |
| AA Ceiling | 22,970 feet (7,000 m) |
| Armor Penetration with 1.96 lbs. (0.899 kg) AP Shell Estimated for "Class B" Homogeneous Armor |
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| Range | Side Armor | Deck Armor | Striking Velocity |
| 0 yards (0 m) | 2.70" (69mm) | --- | 2,890 fps (881 mps) |
| 2,000 yards (1,829 m) | 1.20" (30mm) | N/A | N/A |
| 4,000 yards (3,658 m) | 0.60" (15mm) | N/A | N/A |
| 6,000 yards (5,486 m) | 0.45" (11mm) | N/A | N/A |
| Mount / Turret Data | |||
| Designation | Mark 1 | Twin Mark 2 | Quad Mark 4 Quad |
| Weight | (no shield) 9,800-13,000 lb. (4445-5897 kg) | 23,200-23,800 lb. (10,524-10,796 kg) | 22,795 -24,553 lb. (10,340-11,137 kg) |
| Elevation | -15 / +90 degrees | -15 / +90 degrees | -15 / +90 degrees |
| Elevation Rate | 24 degrees / second | 24 degrees / second | 50 degrees / second |
| Train | 360 degrees | 360 degrees | 360 degrees |
| Train Rate | 26 degrees /second | 26 degrees / second | 50 degrees / second |
| Recoil | 8-9 in (20-22 cm) | ||
| Notes | |||
| Notes on other USA-built Weapons The Mark 3 is the adapted army single air-cooled gun with a weight of 2,440 lbs. (1,107 kg) for the manually trained and 4,200 lbs. (1,905 kg) for the later power driven mount. The Mark 3 Mod 9 is a rebuilt single USA Army type gun for one man operation on river and coastal patrol craft. It is power operated and stabilized and can use a 48 round drum magazine. This was installed aboard 17 PB Mark III Sea Spectre patrol boats in the mid 1980s. |
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| Notes on British-built Weapons Serious British interest in this weapon was first shown by the Army in 1933 and was followed by an order for 100 guns in 1937. Later, a manufacturing license was purchased from Bofors. The British considered this weapon to be at least twice as effective as the 2-pdr. against torpedo bombers but not much better against kamikazes. The British version is officially listed as 56.3 calibers long. The Mark III* mounting was the army design adapted for Naval use and widely used, with some 500 in service at the end of World War II. The Mark IV was derived from the Hazemeyer triaxial mounting which had its origins in the arrival in Britain of the Dutch minelayer Willem van der Zaan in 1940. This mounting utilized a track and pinion system for elevating and training and was powered via a Ward-Leonard system for automatic target tracking. This mounting was advanced for its day but it was somewhat delicate for destroyers or sloops, and the later STAAG and Buster designs were very much heavier. The Boffin mounting was a twin 2 cm Oerlikon mounting modified to take a single Bofors 4 cm. The Mark V was intended from the beginning for naval use but the first production order was not placed until May 1945, after Germany had surrendered. This was a twin power operated mount with elevation limits of -15 / +90 and weighing 6.397 tons (7.5 mt) with 12 four-round clips carried on mount. The Mark VI was a sextuple mount that used a 36 round ammo tray for each gun instead of the usual 4 round clips. The Mark VII was an adapted army single mount with a weight of 3 tons (3.05 mt). The Mark IX is an upgraded Mark VII with electric drive and has 6 clips on mount. All British versions of the Bofors gun except the Mark 6 could accommodate 2 standard four-round clips plus two loose rounds between them for a total of ten rounds in the feeder. Australia uses the Mark VII fitted with a locally designed upgrade package on Fremantle patrol boats. Elevation: -5 / +90 degrees with a rate of 40 degrees per second. Train: 360 degrees with a Train Rate of 20 degrees per second. The British STAAG twin mounting using the type 262 radar was very accurate, but also very unreliable. This was mainly due to the poor decision to mount the radar directly to the weapons platform, thus subjecting the tube-based radar system to the high vibrations inherent in firing large-caliber automatic weapons. The Buster twin was another WWII attempt at a self-contained mounting, but this weighed approximately 20 tons (20.3 mt), far too much for only a twin arrangement, and was cancelled. |
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| Notes on South Korean Weapons South Korea has developed a modification kit for the USA Mark 1 twin mount which adds a stabilization system both to the gun mount and to the Mark 51 FCS which allows the weapons to be used against surface targets. These guns are mounted on FRAM destroyers and locally built corvette's. |
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| Notes on Netherlands Hazemeyer Mounting Hazemeyer was a Dutch subsidiary of Siemens Halske. Prior to WWII, this firm developed a very advanced triaxial mounting together with a tachymetric control system. As noted above, upon the Dutch defeat in 1940, this mounting was brought to Britain where it was immediately introduced into production. |
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| Notes on German Weapons Introduced into service in 1944. As far as is known, only single mountings were ever used on warships. |
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| Notes on Japanese Weapons The Type 5 (Model 1945) originated from the capture of a British Bofors and single hand-worked mounting at Singapore in 1942. A Japanese copy underwent prototype firing trials in 1943 and limited production began in that year, but the gun was never perfected and it did not go into service. However, some 5 to 10 weapons a month were being produced in late 1944, apparently for service evaluation. The main alteration from the Bofors design was to increase the barrel length from 88.58 in (2.250 m) to 94.49 in (2.400 m). It should be noted that the Japanese Model number system, normally based upon the year the breech design was started, became very chaotic towards the end of WWII, with new weapons having Model years that had no relationship to the actual year the breech was started. Some were apparently chosen simply to fill in missing years in the series. |
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