Bofors 40 mm gun
From Wikipedia, the free encyclopedia
| Bofors 40 mm gun | |
|---|---|
 Bofors 40 mm/L60. This example includes the British-designed Stiffkey Sight, being operated by the aimer standing to the right of the loader (turned sideways). It operates the trapeze seen above the sights, moving the sights to adjust for lead. |
|
| Type | autocannon |
| Place of origin | Sweden |
| Service history | |
| Wars | WW2 |
| Specifications | |
| Crew | dependent on use |
|
|
|
| Shell | 40 x 311R |
| Caliber | 40 mm |
| Carriage | 522 kg |
| Rate of fire | 120 round/min |
| Muzzle velocity | 881 m/s |
| Maximum range | 7,160 m (AA) |
The Bofors 40 mm gun is a famous anti-aircraft auto-cannon designed by the Swedish firm of Bofors. It was one of the most popular medium-weight anti-aircraft systems during World War II, used by most of the western Allies as well as various other forces. It is often referred to simply as the Bofors gun.
Contents |
[edit] 40 mm L/60
[edit] Development
The Swedish Navy purchased a number of 2 pounder Pom-Poms from Vickers as anti-aircraft guns in 1922. Looking for a smaller hand-swung weapon to complement the heavy Vickers, they asked Bofors A.B. to develop a 20 mm weapon based on a similar mechanism (and generally similar to the Vickers 1-pdr). Although this 20 mm design was not put into production, the Navy quickly soured on the 2 pdr, and approached Bofors in 1929 about the development of a much more capable replacement.
Bofors was initially reluctant, the Swedish Navy being a fairly small market, but the Navy eventually agreed to pay for the development of a prototype. Bofors responded with a gun that was, to some extent, a smaller version of a 57 mm (6-pounder) semi-automatic gun developed as an anti-torpedo boat weapon in the late 1800s by Finspong before Bofors drove them out of business. Their first prototype was in fact a re-barreled Nordenfelt version of the Finspong gun, adding an auto-loader mechanism similar to the Vickers "machine gun" system using a moving bolt.
Testing of the prototype in 1929 demonstrated the major problem was feeding the weapon in order to maintain a reasonable rate of fire. A bolt that was heavy enough to handle the stresses of firing the large round was too heavy to move quickly enough to fire quickly. One interesting attempt to solve this problem used zinc shell cases that burned up when fired. This proved to leave heavy zinc deposits in the barrel, and had to be abandoned. Instead they experimented with a newer mechanism that simply "threw" the rounds into the breach from the rear without guiding them, the empty cases simply falling out to the rear when the breach was opened. This proved to be the solution they needed.
During this period Krupp purchased a one-third share of Bofors. Krupp engineers started the process of updating the Bofors factories to use modern equipment and metallurgy, but the 40 mm project was kept secret. Nevertheless, many sources claim that the 40 mm design was in fact adapted from a Krupp weapon. However the only German weapon of similar calibre (and role) was the 3.7 cm FlaK 43, made by Rheinmetall; it appears historians connected the development of the 40 mm and German 37 mm weapons without any supporting evidence. It should be pointed out these two weapons are quite different from each other and share few, if any, features.
By June 1930 testing with the prototype was complete, and Bofors reported that full-scale development could begin. A prototype was completed and fired in November 1931, and by the middle of the month it was firing strings of two and three rounds. Changes to the feed mechanism were all that remained, and by the end of the year it was operating at 130 rounds per minute. Continued development was needed to turn it into a weapon suitable for production, which was completed in October 1933. Since acceptance trials had been passed the year before, this became known as the 40 mm akan M/32. Most forces referred to it as the Bofors 40 mm L/60, although the barrel was actually 56.1 calibres in length.
The gun fired a 2 lb (900 g) high explosive 40 x 311R (rimmed) shell at 2,800 ft/s (850 m/s). The rate of fire was normally about 120 rounds per minute, which improved slightly when the barrels were closer to the horizontal as gravity assisted the feeding. In practice firing rates were closer to 80–100 rpm, as the rounds were fed into the breech from four round clips which had to be replaced by hand. The maximum attainable ceiling was 23,600 ft (7,200 m), but the practical maximum was about 12,500 ft (3,800 m).
The gun was also notable due to its advanced sighting system. The trainer and layer were both provided with reflector sights for aiming, which a third crewmember standing behind them "adjusted" for lead using a simple mechanical computer. Power for the sights was supplied from a 6V battery.
With the design now reaching completion, the Swedish Navy once again decided it needed a smaller hand-swung weapon of 13 mm–25 mm, and started testing various designs from foreign suppliers. With the 40 mm well along in development, Bofors offered a 25 mm version in 1932, which was eventually selected as the 25 mm akan M/32. The first version of the 40 mm the Navy ordered featured a shorter barrel intended for use on submarines. The barrel was shorter at 42 calibres long, with the effect of reducing the muzzle velocity to about 700 m/s. When not in use, the gun was pointed directly up and retracted into a watertight cylinder.
Interestingly the first order for the "real version" was made by the Dutch Navy, who ordered five twin-gun mounts for the cruiser de Ruyter in August 1934. These guns were stabilized using a unique system known as the Hazemeyer mount, in which one set of layers aimed the gun, while a second manually stabilized the platform the gun sat on. All five mounts were operated by one fire control system.
Bofors also started the development of a suitable towable carriage which they displayed in April 1935 at a show in Belgium. The carriage caused something of a stir, as the gun could be fired from the carriage with no setup required, although with limited accuracy. If time was available the gunners used the tow-bar and muzzle lock as levers, raising the wheels off the ground and thereby lowering the gun onto supporting pads. Two additional legs folded out to the sides, and the platform was then leveled with hand cranks. The entire setup process could be completed in under a minute.
Orders for the land based versions were immediate, starting with an order for eight weapons from Belgium in August 1935, and followed by a flood of orders from other forces including Poland, Norway, and Finland. It was only accepted into the Swedish Army the next year, known as the 40 mm lvakan m/36, the lower-case m indicating an Army model as opposed to the capital M for Navy.
[edit] British versions
[edit] Army versions
The British Army had first examined the weapon when they received a number of Polish-built examples in 1937 for testing, known as the QF 40 mm Mark I (QF standing for "Quick Firing"), or Mark I/2 after a minor change to the flash hider. A license was soon acquired and the arduous task of converting the gun from metric to imperial measurements was started. While this was taking place they also made numerous changes to the design to make it more suitable to mass production—the original Bofors design was intended to be hand-assembled, and many parts were labeled "file to fit on assembly", requiring many manhours of work to complete.
Testing showed that aiming the guns was a serious problem against modern high-speed aircraft. Although the gun could be trained quickly, aiming accurately while doing so proved difficult. In order to address this, the British introduced a complex mechanical analogue computer, the Kerrison Director, which drove the laying electrically. A three-man team operated the Director simply by pointing it at the target and dialing in estimates for range and various atmospheric conditions, the gunners being reduced to simply loading the clips. Backup sights were then fitted, consisting of simple ring-and-post sights in place of the former reflector sights.
In this form, the QF 40 mm Mark III (there was no Mk II), became the Army's standard light AA weapon, operating alongside their 3-inch and 3.7-inch heavy weapons. The gun was considered so important to the defence of England after the fall of France in 1940 that a movie, The Gun, was produced to encourage machinists to work harder and complete more of them. By the end of the war total production from British, Canadian, and Australian factories was over 2,100, while US lend-lease examples added about 150.
In combat it was found that the Kerrison was simply too difficult to set up to use in many situations, as well as making logistics more complex due to the need to keep its electrical generator supplied with fuel. In most engagements only the "pancake sights" were used, without any form of correction, making the British versions less capable than those used by other forces. Eventually an anti-aircraft gunnery school on the range at Stiffkey on the Norfolk coast delivered a workable solution, a simple trapeze-like arrangement that moved the pancake sights to offer lead correction, operated by a new crewmember standing behind the left-hand layer. The Stiffkey Sight was sent out to units in 1943, arriving in Canadian units in the midst of the Battle of the Aleutian Islands. A final wartime change to the elevation mechanism resulted in the QF 40 mm Mark XII.
The Army also experimented with various self-propelled AA systems, SPAAGs, based on various tank chassis. Changes to the breech for this role created the QF 40 mm Mark VI, which was used on the Crusader to produce the Crusader III AA Mark I. They also designed a much lighter two-wheeled carriage for airborne use. But the main self-propelled version of the Bofors was with the gun set on the chassis of a Morris Commercial four-wheel drive lorry. Such guns were used in support of Army divisions to provide swift protection again air attack without the need to unlimber. They saw service in North West Europe, where six SP Bofors of 92nd (Loyals) Light Anti-Aircraft Regiment, Royal Artillery, landed with 3rd British Infantry Division on Sword Beach on D-Day to protect the vital bridges over the Caen Canal and Orne River (Pegasus Bridge and Horsa Bridge), shooting down 17 German planes. Later in the campaign, SP Bofors were used extensively for ground shoots as well as in an anti-aircraft role. In British army service the Bofors found a highly specialised role: during the North Africa Campaign at the Battle of El Alamein, they were used to fire tracer horizontally to mark safe paths for units through the German minefields.
[edit] Naval versions
The Royal Navy also made extensive use of the Bofors. Their first examples were air-cooled versions quickly adapted to ships during the withdrawal from Norway. With the fall of the west in 1940 the Dutch minelayer Willem van der Zaan brought them their first example of a water-cooled gun on their Hazemeyer tri-axially stabilised mounting. Locally produced examples started arriving in 1942, known as the QF 40 mm Mark IV for use in twin-mounts, or the QF 40 mm Mark V for single mounts. The Navy ran through a variety of versions of the basic Bofors gun over the war, including the Mark VII to Mark XI. Somewhat confusingly, the Royal Navy's home grown light anti-aircraft weapon, the 2-pounder gun, also had a calibre of 40 mm, but was referred to as the QF 2 pdr.
The designation of models in Royal Navy service is confused by the fact that the gun and its mounting received separate mark numbers. The following mountings were used;
- Mark I—twin mounting based on American design and using American built guns, not widely fitted. Fitted for remote fire control.
- Mark II—quadruple version similar to Mark I
- Mark III—a navalised version of the Army single mounting, hand worked elevation and training.
- Mark IV—a tri-axially stabilised twin mounting copied from, and usually known as, the "Hazemeyer". It had on-mounting fire control, and was usually fitted with Radar Type 282 to provide target range information.
- Mark V—twin mounting, that superseded and eventually replaced the Mark IV, often referred to as the "utility" mounting. This was a simplified, unstabilised mounting based on the American twin mounting Mark I, and was designed for remote fire control.
- Mark VI— a six-barrelled weapon feeding from large trays instead of clips and designed for remote control from a dedicated radar-equipped director.
- Mark VII—a single barrelled, hydraulically powered mounting that superseded the Mark III and entered service in 1945.
- Mark IX—Mark VII mount modified to electrical power, as the Mounting Mark IX, and in this form saw service in the Falklands War.
Confusingly, the Mounting Mark V (Mark VC for Canadian built examples) for the 20 mm Oerlikon and QF 2 pounder guns was also adopted as (initially) an interim mount for the Bofors. It was a single barrelled mounting with hydraulic power, and was known as the Boffin. The final British Bofors mounting that saw service was the STAAG. Standing for Stabilised Tachymetric Anti Aircraft Gun this was an enormous twin-barrelled affair that, as the name indicates, was stabilised and carried its own tachymetric (i.e. predictive) fire control system, based around the centimetric Radar Type 262. This latter set was capable of "locking on" to a target. Unfortunately this mounting was grossly overweight (17.5 tons) and it was found that the high-vibration environment of the gun mounting was a less than ideal location for sensitive valve electronics and mechanical computers. STAAG Mark I carried the radar dish over the gun barrels where it was subject to damage during firing, therefore STAAG Mark II shifted the set to the roof of the control cabin. An ambitious weapon that was ahead of its time, STAAG was ultimately too difficult to maintain in the harsh environment of a warship and was later replaced by the Mounting Mark V with the fire control equipment located remotely, the single Mark VII and ultimately, with the Sea Cat missile.
[edit] US versions
[edit] Naval
The US Navy's Bureau of Ordnance purchased a twin-mount air-cooled example directly from Bofors, which arrived in New York on 28 August 1940. During that month another Dutch ship, the van Kinsbergen, demonstrated the Hazemeyer mount to Navy observers. The gun was quickly chosen as the Navy's standard anti-aircraft weapon, and the Navy secretly imported a set of Imperial designs from England and started production illegally. A formal contract with Bofors followed in June 1941. The resulting Mark 1 and Mark 2 weapons were intended for the left and right side of a twin mount, respectively.
[edit] Army
The US Army had recently introduced a 37 mm gun of their own design, but found it to be of limited performance. Six British guns were imported for testing, along with the Kerrison Directors, and proved to be superior in all areas. In order to supply both the Army and Navy with much greater numbers of the guns, Chrysler was brought in to be a major producer. Over the lifetime of the production, their engineers introduced numerous additional changes to improve mass production, eventually reducing the overall time needed to build a gun by half.
[edit] Captured examples
The Wehrmacht used a number of Bofors guns which had been captured in Poland and France. The Kriegsmarine also operated some guns obtained from Norway.
Japan captured a number of Bofors guns in Singapore and put them into production as the Type 5.
[edit] Continued use
Although the L/60 was later replaced in production by the L/70, the L/60 remained in front-line service well into the 1980s. In most cases these were the airborne versions, as a suitable replacement in this role did not come along until the introduction of truly effective MANPADS missiles in the 1980s. L/60's are still used in the USAF's AC-130 gunships in the air-to-ground role but are currently being replaced by 30 mm Bushmaster II due a lack of replacement parts and for commonality with the rest of the armed services.
The L/60 saw active service with the Royal Navy in the 1982 Falklands War and continued to be used into the 1990s, when it was replaced by modern 20- and 30-mm artillery.
The Canadian Forces also used Bofors on their surface fleet, but removed the guns in the late 1980s when they were considered to be outdated. In a somewhat embarrassing episode, the navy was forced to scour various military museums across Canada to re-equip their fleet during the Gulf War, as replacements had never been purchased. The L/60 Bofors continue to be the main armament of the Canadian Maritime Coastal Defence Vessel(MCDV), although the navy is in the midst of a search for a suitable replacement.[1]
In August 2006, the French navy uses L/60 on more than twenty ships (patrols and auxiliaries).
The Royal Australian Navy uses the L/60 on still active Fremantle class patrol boats.
Ships of the Norwegian and Icelandic Coast Guards continue to use the 40mm Bofors gun.
[edit] 40 mm L/70
By the end of World War II, jet aircraft had so increased the speed of attack that the Bofors simply could not get enough rounds into the air to counter the aircraft before it had already flown out of range. In order to counter these threats, the gun would have to have longer range and a higher rate of fire, thereby increasing the number of rounds fired over the period of an engagement. Bofors considered either updating the 40 mm, or alternately making a much more powerful 57 mm design, and in the end did both.
The new 40 mm design used a larger 40 x 364R round firing a slightly lighter 870g shell at a much higher 1,030 m/s muzzle velocity. The rate of fire was increased to 240 rounds per minute, unusually high for such a large round. Additionally the carriage was modified to be power-laid, the power being supplied by a generator placed on the front of the carriage. The first version was produced in 1947, accepted in 1948 as the 40 mm lvakan m/48, and entered Swedish service in 1951. Additional changes over the years have improved the firing rate first to 300 rpm, and later to 330.
Foreign sales started, as they had in the past, with Holland and Great Britain. In November 1953 it was accepted as the NATO standard anti-aircraft gun, and was soon produced in the thousands. The L/70 was also used as the basis for a number of SPAAG's, notably the US Army's infamous M247 Sergeant York, which proved to be unable to hit even hovering drone targets.
Breda (now Oto Melara) of Italy uses the Bofors 40 mm L/70 gun in its anti-aircraft weapon system for the Italian Army and Navy. A newer development from Breda, the Fast Forty, has nearly doubled the rate of fire to 450 rpm, normally equipped with a 43 round clip, or a 101 round clip for naval use.
In the Swedish Army Combat Vehicle 90 there is a cartridge fed, automatic version of the L/70 gun installed. It is also interesting to note that the gun, in order to fit inside the vehicle, is mounted upside down. New armour piercing and programmable ammunition have also been developed.
[edit] References
[edit] In-line
- ^ Stephen Priestley. The Kingston Class: 'Mid-Life' or Move Over for the MCDV?. Canadian American Strategic Review. Retrieved on February 19, 2007.
[edit] General
- Campbell, John. Naval Weapons of World War Two. Annapolis: Naval Institute Press, 1985. ISBN 0-87021-459-4.
[edit] See also
[edit] External links
