The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, is called a "star engine" in some languages; the radial configuration was used for aircraft engines before gas turbine engines became predominant. Since the axes of the cylinders are coplanar, the connecting rods cannot all be directly attached to the crankshaft unless mechanically complex forked connecting rods are used, none of which have been successful. Instead, the pistons are connected to the crankshaft with a master-and-articulating-rod assembly. One piston, the uppermost one in the animation, has a master rod with a direct attachment to the crankshaft; the remaining pistons pin their connecting rods' attachments to rings around the edge of the master rod. Extra "rows" of radial cylinders can be added in order to increase the capacity of the engine without adding to its diameter.
Four-stroke radials have an odd number of cylinders per row, so that a consistent every-other-piston firing order can be maintained, providing smooth operation. For example, on a five-cylinder engine the firing order is 1, 3, 5, 2, 4, back to cylinder 1. Moreover, this always leaves a one-piston gap between the piston on its combustion stroke and the piston on compression; the active stroke directly helps compress the next cylinder to fire. If an number of cylinders were used, an timed firing cycle would not be feasible; the prototype radial Zoche aero-diesels have an number of cylinders, either four or eight. The radial engine uses fewer cam lobes than other types; as with most four-strokes, the crankshaft takes two revolutions to complete the four strokes of each piston. The camshaft ring is geared to spin slower and in the opposite direction to the crankshaft; the cam lobes exhaust. For example, four cam lobes serve all five cylinders, whereas 10 would be required for a typical inline engine with the same number of cylinders and valves.
Most radial engines use overhead poppet valves driven by pushrods and lifters on a cam plate, concentric with the crankshaft, with a few smaller radials, like the Kinner B-5 and Russian Shvetsov M-11, using individual camshafts within the crankcase for each cylinder. A few engines use sleeve valves such as the 14-cylinder Bristol Hercules and the 18-cylinder Bristol Centaurus, which are quieter and smoother running but require much tighter manufacturing tolerances. C. M. Manly constructed a water-cooled five-cylinder radial engine in 1901, a conversion of one of Stephen Balzer's rotary engines, for Langley's Aerodrome aircraft. Manly's engine produced 52 hp at 950 rpm. In 1903–1904 Jacob Ellehammer used his experience constructing motorcycles to build the world's first air-cooled radial engine, a three-cylinder engine which he used as the basis for a more powerful five-cylinder model in 1907; this was made a number of short free-flight hops. Another early radial engine was the three-cylinder Anzani built as a W3 "fan" configuration, one of which powered Louis Blériot's Blériot XI across the English Channel.
Before 1914, Alessandro Anzani had developed radial engines ranging from 3 cylinders — early enough to have been used on a few French-built examples of the famous Blériot XI from the original Blériot factory — to a massive 20-cylinder engine of 200 hp, with its cylinders arranged in four rows of five cylinders apiece. Most radial engines are air-cooled, but one of the most successful of the early radial engines was the Salmson 9Z series of nine-cylinder water-cooled radial engines that were produced in large numbers during the First World War. Georges Canton and Pierre Unné patented the original engine design in 1909, offering it to the Salmson company. From 1909 to 1919 the radial engine was overshadowed by its close relative, the rotary engine, which differed from the so-called "stationary" radial in that the crankcase and cylinders revolved with the propeller, it was similar in concept to the radial, the main difference being that the propeller was bolted to the engine, the crankshaft to the airframe.
The problem of the cooling of the cylinders, a major factor with the early "stationary" radials, was alleviated by the engine generating its own cooling airflow. In World War I many French and other Allied aircraft flew with Gnome, Le Rhône, Bentley rotary engines, the ultimate examples of which reached 250 hp although none of those over 160 hp were successful. By 1917 rotary engine development was lagging behind new inline and V-type engines, which by 1918 were producing as much as 400 hp, were powering all of the new French and British combat aircraft. Most German aircraft of the time used water-cooled inline 6-cylinder engines. Motorenfabrik Oberursel made licensed copies of the Gnome and Le Rhône rotary powerplants, Siemens-Halske built their own designs, including the Siemens-Halske Sh. III eleven-cylinder rotary engine, unusual for the period in being geared through a bevel geartrain in the rear end of the crankcase without the crankshaft being mounted to the aircraft's airframe, so that the engine's internal working components (fully in
The Tank, Ram was a cruiser tank designed and built by Canada in the Second World War, based on the U. S. M3 Medium tank chassis. Due to standardization on the American Sherman tank for frontline units, it was used for training purposes and was never used in combat as a gun tank; the chassis was used for several other combat roles however, such as a flamethrower tank, observation post, armoured personnel carrier. Before the loss of the majority of the United Kingdom's tank force in France in 1940 after Dunkirk, it was recognised that tank production in the UK at the start of the war was insufficient and capacity in the US was taken for British needs. So it was necessary that if Canada was to equip with tanks they would have to be manufactured locally. In June 1940 the Canadian Pacific Railway's Angus Shops in Montreal, as the only large firm with spare capacity, had received a contract to produce 300 fitted out Valentine tanks for the British; however the Valentine was an infantry tank and Canada required a cruiser tank for its formed armoured division.
In the end 1,420 Valentines were produced by CPR, most of which were supplied to the USSR. Although the Valentine used a number of American produced parts, its reliance on British components, difficulties in adapting its manufacture to North American methods, other problems such as limitations to the availability of the right type of armour plate affected Valentine production; the Canadian Joint Committee on Tank Development concluded, in September 1940, that its cruiser tank should be based on a US rather than a British design. This would be quicker and allow it to use components in production for the US design; the Canadians were interested in production of the M3 Medium. However the M3 was an interim design. In early 1941 the Canadian Interdepartmental Tank Committee adopted a compromise: to develop a superior design locally but still using the M3 chassis; the British Tank Mission, involved in the modifications of the M3 for British use contributed a tank expert, L. E. Carr, to design a new hull and turret for the Canadian tank which could take a 6-pounder or 75mm gun while retaining the lower hull of the US M3 Medium.
The new hull was cast rather than welded or riveted and lower than that of the M3. The pilot model's turret and upper hull casting was produced in the US by General Steel Castings and they aided the set up of Canadian production. Montreal Locomotive Works was chosen to make the new Canadian M.3 Cruiser Tank and was given the funding to set up the Canadian Tank Arsenal at Longue Pointe. MLW was a subsidiary of the American Locomotive Company, which had experience in producing large castings and another ALCO subsidiary was producing cast hulls for the M3 Medium. Canadian engineers ran into many challenges when developing the tank as Canada had never produced a tank before. Along with the lack of knowledge, it took time for Canadian factories to gear up for the production of many of the Ram's components. Canada relied on United States and British materials to complete the construction of the Ram. Most critically the Ram's Continental engine and transmissions were available only in the USA and these were always in short supply.
The Ram tank was developed with a turret which unlike the US M3 could traverse the main armament 360 degrees. Its cast armoured steel hull gave reinforced protection and, with the driver's seat repositioned to meet British requirements for right-hand drive, lower height. S.-designed chassis and power train ensured its overall reliability. Although it could mount a US 75 mm gun, the preferred armament for the Ram was the QF 6 pounder which had superior armour-piercing capability; as neither the 6 pounder nor the Canadian-designed mounting for it was available, early production were fitted with the 40 mm QF 2-pounder gun. A prototype Ram was completed in June 1941 and general production of the Ram I began in November of the same year; the Ram I and early Ram IIs were fitted with side doors in the hull and an auxiliary machine gun turret in the front. The former weakened the hull and complicated production, the doors and the machine gun turret were discarded in modifications. By February 1942 production had switched to the Ram II model with a 6-pounder gun and continued until July 1943.
In March 1942 a decision had been made to change production over to the automotively-similar M4A1 Sherman tank for all British and Canadian units. Ram production continued due to delay in starting the new M4 production lines and a reluctance to let the plant lie idle. By July 1943 1,948 vehicles plus 84 artillery observation post vehicles had been completed; the official Canadian history of the war compares the Ram to the Ross rifle as examples of unsuccessful Canadian weapon designs. It states that given the Sherman's superiority, in retrospect it would have been better for the United States to produce more tanks, for Canada to have focused on manufacturing more transport vehicles such as the successful Canadian Military Pattern truck designs; the Sexton self-propelled gun based on the Ram chassis, was successful. As built, the Ram was never used in combat as a tank, but was used for crew training in Great Britain up to mid 1944; the observation post vehicles and Armoured Personnel Carrier, gun tractor, munitions carrier versions of the Ram saw considerable active service in North West Europe.
These tanks were rebuilt by Canadian Army workshops in the United Kingdom. Conversions of Ram
The M4 Sherman Medium Tank, M4, was the most used medium tank by the United States and Western Allies in World War II. The M4 Sherman proved to be reliable cheap to produce, available in great numbers. Thousands were distributed through the Lend-Lease program to the British Commonwealth and Soviet Union; the tank was named by the British for the American Civil War general William Tecumseh Sherman. The M4 Sherman evolved from the M3 Medium Tank, which had its main armament in a side sponson mount; the M4 retained much of the previous mechanical design, but put the main 75 mm gun in a traversing turret. One feature, a one-axis gyrostabilizer, was not precise enough to allow firing when moving but did help keep the reticle on target, so that when the tank did stop to fire, the gun would be aimed in the right direction; the designers stressed mechanical reliability, ease of production and maintenance, standardization of parts and ammunition in a limited number of variants, moderate size and weight.
These factors, combined with the Sherman's then-superior armor and armament, outclassed German light and medium tanks fielded in 1939–42. The M4 went on to be produced in large numbers, it spearheaded many offensives by the Western Allies after 1942. When the M4 tank went into combat in North Africa with the British Army at El Alamein in late 1942, it increased the advantage of Allied armor over Axis armor and was superior to the lighter German and Italian tank designs. For this reason, the US Army believed that the M4 would be adequate to win the war, little pressure was exerted for further tank development. Logistical and transport restrictions, such as limitations imposed by roads and bridges complicated the introduction of a more capable but heavier tank. Tank destroyer battalions using vehicles built on the M4 hull and chassis, but with open-topped turrets and more potent high-velocity guns entered widespread use in the Allied armies. By 1944, most M4 Shermans kept their dual-purpose 75 mm gun.
By the M4 was inferior in firepower and armor to increasing numbers of German heavy tanks, but was able to fight on with the help of considerable numerical superiority, greater mechanical reliability, better logistical support, support from growing numbers of fighter-bombers and artillery pieces. Some Shermans were produced with a more capable gun, the 76 mm gun M1, or refitted with an Ordnance QF 17-pounder by the British; the relative ease of production allowed large numbers of the M4 to be manufactured, significant investment in tank recovery and repair units allowed disabled vehicles to be repaired and returned to service quickly. These factors combined to give the Allies numerical superiority in most battles, many infantry divisions were provided with M4s and tank destroyers. After World War II, the Sherman the many improved and upgraded versions, continued to see combat service in many conflicts around the world, including the UN forces in the Korean War, with Israel in the Arab–Israeli wars with South Vietnam in the Vietnam War, on both sides of the Indo-Pakistani War of 1965.
The U. S. Army Ordnance Department designed the M4 medium tank as a replacement for the M3 medium tank; the M3 was an up-gunned development of the M2 Medium Tank of 1939, in turn derived from the M2 light tank of 1935. The M3 was developed as a stopgap measure. While it was a big improvement when tried by the British in Africa against early German tanks, the placement of a 37 mm gun turret on top gave it a high profile, the unusual side-sponson mounted main gun, with limited traverse, could not be aimed across the other side of the tank. Though reluctant to adopt British weapons into their arsenal, the American designers were prepared to accept proven British ideas. British ideas, as embodied in a tank designed by the Canadian General Staff influenced the development of the American Sherman tank. Before long American military agencies and designers had accumulated sufficient experience to forge ahead on several points. In the field of tank armament the American 75 mm and 76 mm dual-purpose tank guns won the acknowledgement of British tank experts.
Detailed design characteristics for the M4 were submitted by the Ordnance Department on 31 August 1940, but development of a prototype was delayed while the final production designs of the M3 were finished and the M3 entered full-scale production. On 18 April 1941, the U. S. Armored Force Board chose the simplest of five designs. Known as the T6, the design was a modified M3 hull and chassis, carrying a newly designed turret mounting the M3's 75 mm gun; this would become the Sherman. The Sherman's reliability resulted from many features developed for U. S. light tanks during the 1930s, including vertical volute spring suspension, rubber-bushed tracks, a rear-mounted radial engine with drive sprockets in front. The goals were to produce a fast, dependable medium tank able to support infantry, provide breakthrough striking capacity, defeat any tank in use by the Axis nations; the T6 prototype was completed on 2 September 1941. The upper hull of the T6 was a single large casting, it featured a single overhead hatch for the driver, a hatch in the side of the hull.
In the M4A1 production model, this large casting was maintained, although the side hatch was eliminated and a second overhead hatch was added for the assistant driver. The modified T6 was standardized as the M4, production began in February 1942; the cast hull models would be re-standardized as M4A1, with the first welded hull models receiving the designation M4. In August, 1942, a variant of the M4 was put forth by the Detroit Arsenal to ha
A shell is a payload-carrying projectile that, as opposed to shot, contains an explosive or other filling, though modern usage sometimes includes large solid projectiles properly termed shot. Solid shot may contain a pyrotechnic compound if a spotting charge is used, it was called a "bombshell", but "shell" has come to be unambiguous in a military context. All explosive- and incendiary-filled projectiles for mortars, were called grenades, derived from the pomegranate, so called because the many-seeded fruit suggested the powder-filled, fragmenting bomb, or from the similarity of shape. Words cognate with grenade are still used for an artillery or mortar projectile in some European languages. Shells are large-caliber projectiles fired by artillery, combat vehicles, warships. Shells have the shape of a cylinder topped by an ogive-shaped nose for good aerodynamic performance with a tapering base, but some specialized types are quite different. Solid cannonballs did not need a fuse, but hollow munitions filled with something such as gunpowder to fragment the ball, needed a fuse, either impact or time.
Percussion fuses with a spherical projectile presented a challenge because there was no way of ensuring that the impact mechanism contacted the target. Therefore, shells needed a time fuse, ignited before or during firing and burned until the shell reached its target; the earliest record of shells being used in combat was by the Republic of Venice at Jadra in 1376. Shells with fuses were used at the 1421 siege of St Boniface in Corsica; these were two hollowed hemispheres of bronze held together by an iron hoop. Written evidence for early explosive shells in China appears in the early Ming Dynasty Chinese military manual Huolongjing, compiled by Jiao Yu and Liu Bowen sometime before the latter's death, a preface added by Jiao in 1412; as described in their book, these hollow, gunpowder-packed shells were made of cast iron. At least since the 16th century grenades made of ceramics or glass were in use in Central Europe. A hoard of several hundred ceramic grenades were discovered during building works in front of a bastion of the Bavarian city of Ingolstadt, Germany dated to the 17th century.
Lots of the grenades igniters. Most the grenades were intentionally dumped in the moat of the bastion before the year 1723. An early problem was that there was no means of measuring the time to detonation — reliable fuses did not yet exist and the burning time of the powder fuse was subject to considerable trial and error. Early powder burning fuses had to be loaded fuse down to be ignited by firing or a portfire put down the barrel to light the fuse. Other shells were wrapped in bitumen cloth, which would ignite during the firing and in turn ignite a powder fuse. Shells came into regular use in the 16th century, for example a 1543 English mortar shell was filled with'wildfire'. By the 18th century, it was known that the fuse toward the muzzle could be lit by the flash through the windage between the shell and the barrel. At about this time, shells began to be employed for horizontal fire from howitzers with a small propelling charge and, in 1779, experiments demonstrated that they could be used from guns with heavier charges.
The use of exploding shells from field artillery became commonplace from early in the 19th century. Until the mid 19th century, shells remained as simple exploding spheres that used gunpowder, set off by a slow burning fuse, they were made of cast iron, but bronze, lead and glass shell casings were experimented with. The word bomb encompassed them at the time, as heard in the lyrics of The Star-Spangled Banner, although today that sense of bomb is obsolete; the thickness of the metal body was about a sixth of their diameter and they were about two thirds the weight of solid shot of the same caliber. To ensure that shells were loaded with their fuses toward the muzzle, they were attached to wooden bottoms called sabots. In 1819, a committee of British artillery officers recognized that they were essential stores and in 1830 Britain standardized sabot thickness as a half inch; the sabot was intended to reduce jamming during loading. Despite the use of exploding shell, the use of smoothbore cannons firing spherical projectiles of shot remained the dominant artillery method until the 1850s.
The mid 19th century saw a revolution in artillery, with the introduction of the first practical rifled breech loading weapons. The new methods resulted in the reshaping of the spherical shell into its modern recognizable cylindro-conoidal form; this shape improved the in-flight stability of the projectile and meant that the primitive time fuzes could be replaced with the percussion fuze situated in the nose of the shell. The new shape meant that further, armor-piercing designs could be used. During the 20th Century, shells became streamlined. In World War I, ogives were two circular radius head - the curve was a segment of a circle having a radius of twice the shell caliber. After that war, ogive shapes became more elongated. From the 1960s, higher quality steels were introduced by some countries for their HE shells, this enabled thinner shell walls with less weight of metal and hence a greater weight of explosive. Ogives were further elongated to improve their ballistic performance. Advances in metallurgy in the industrial era allowed for the construction of rifled breech-loading guns that could fire at a much greater muzzle velocity.
After the British artillery was shown up in the Cri
Indirect fire is aiming and firing a projectile without relying on a direct line of sight between the gun and its target, as in the case of direct fire. Aiming is performed by calculating azimuth and inclination, may include correcting aim by observing the fall of shot and calculating new angles. There are two dimensions in aiming a weapon: In the horizontal plane; the projectile trajectory is affected by atmospheric conditions, the velocity of the projectile, the difference in altitude between the firer and the target, other factors. Direct fire sights may include mechanisms to compensate for some of these. Handguns and rifles, machine guns, anti-tank guns, tank main guns, many types of unguided rockets, guns mounted in aircraft are examples of weapons designed for direct fire. NATO defines indirect fire as "Fire delivered at a target which cannot be seen by the aimer." The implication is that azimuth and/or elevation'aiming' is done using instrumental methods. Hence indirect fire means applying'firing data' to azimuth and elevation sights and laying these sights.
Indirect fire can be used when the target is visible from the firing position. However, it is used when the target is at longer range and invisible to the firer due to the terrain. Longer range uses a higher trajectory, in theory maximum range is achieved with an elevation angle of 45 degrees. Indirect fire is most associated with field artillery and mortars, it is used with naval guns against shore targets, sometimes with machine guns, has been used with tank and anti-tank guns and by anti-aircraft guns against surface targets. It is reasonable to assume that original purpose of indirect fire was to enable fire from a'covered position', one where gunners can not be seen and engaged by their enemies; the concealment aspect remains important, but from World War I important was the capability to concentrate the fire of many artillery batteries at the same target or set of targets. This became important as the range of artillery increased, allowing each battery to have an ever-greater area of influence, but required command and control arrangements to enable concentration of fire.
The physical laws of ballistics means that guns firing larger and heavier projectile can send them further than smaller-calibre guns firing lighter shells. By the end of the 20th century, the typical maximum range for the most common guns was about 24 to 30 km, up from about 8 km in World War I. During World War I, covered positions moved further back and indirect fire evolved to allow any point within range to be attacked, firepower mobility, without moving the firers. If the target cannot be seen from the gun position, there has to be a means of identifying targets and correcting aim according to fall of shot; the position of some targets may be identified by a headquarters from various sources of information: observers on the ground, in aircraft, or in observation balloons. The development of electrical communication immensely simplified reporting, enabled many dispersed firers to concentrate their fire on one target; until the introduction of smart munitions the trajectory of the projectile could not be altered once fired.
Indirect arrow fire by archers was used by ancient armies. It was used during both battles and sieges. For several centuries Coehorn mortars were fired indirectly because their fixed elevation meant range was determined by the amount of propelling powder, it is reasonable conjecture that if these mortars were used from inside fortifications their targets may have been invisible to them and therefore met the definition of indirect fire. It could be argued that Niccolò Tartaglia's invention of the gunner's quadrant in the 16th century introduced indirect fire guns because it enabled gunlaying by instrument instead of line of sight; this instrument was a carpenter's set square with a graduated arc and plumb-bob placed in the muzzle to measure an elevation. There are suggestions, based on an account in Livre de Canonerie published in 1561 and reproduced in Revue d'Artillerie of March 1908, that indirect fire was used by the Burgundians in the 16th Century; the Russians seem to have used something similar at Paltzig in 1759 where they fired over trees, their instructions of the time indicate this was a normal practice.
These methods involved an aiming point positioned in line with the target. The earliest example of indirect fire adjusted by an observer seems to be during the defence of Hougoumont in the Battle of Waterloo where a battery of the Royal Horse Artillery fired an indirect Shrapnel barrage against advancing French troops using corrections given by the commander of an adjacent battery with a direct line of sight. Modern indirect fire dates from the late 19th century. In 1882 a Russian, Lt Col K. G. Guk, published Field Artillery Fire from Covered Positions that described a better method of indirect laying. In essence, this was the geometry of using angles to aiming points that could be in any direction relative to the target; the problem was the lack of an azimuth instrument to enable it. The Germans sol
The Bishop was a British self-propelled artillery vehicle based on the Valentine tank and armed with the 25 pounder gun-howitzer, which could fire an 87.6 mm 11.5 kg HE shell or an armour-piercing shell. A result of a rushed attempt to create a self-propelled gun, the vehicle had numerous problems, was produced in limited numbers and was soon replaced by better designs; the rapid manoeuvre warfare practiced in the North African Campaign led to a requirement for a self-propelled artillery vehicle armed with the 25-pounder gun-howitzer. In June 1941, the development was entrusted to the Birmingham Railway Wagon Company. A prototype was ready for trials by August and 100 were ordered by November 1941; the result was a vehicle with the formal title: "Ordnance QF 25-pdr on Carrier Valentine 25-pdr Mk 1". The vehicle was based on the Valentine II hull, with the turret replaced by a fixed boxy superstructure with large rear doors, it was nicknamed the "Bishop" for its high mitre-like superstructure.
Into this superstructure the 25-pounder gun-howitzer was fitted. As a consequence of the gun mounting, the resulting vehicle had high silhouette, a disadvantage in desert warfare; the maximum elevation for the gun was limited to 15 degrees, reducing the range to 6,400 yards, about half that of the same gun on a wheeled carriage. The maximum depression was 5 degrees, traverse was 8 degrees, the vehicle could carry a Bren light machine gun. By July 1942, 80 Bishops had been built. Turkey received 48 Bishops in 1943; the Bishop first saw action during the Second Battle of El Alamein in North Africa and remained in service during the early part of the Italian Campaign. Due to its limitations and the Valentine's characteristic slow speed, the Bishop was poorly received. To increase range, crews would build large earthen ramps and run the Bishop onto them, tilting the vehicle back to increase the elevation; the Bishop was replaced by the M7 Priest and Sexton when those became available in sufficient numbers and surviving Bishops were diverted for training in self-propelled gun tactics.
A British self-propelled gun armed with the Ordnance QF 25-pounder in design from 1941 was nicknamed "the Bishop" as its appearance was said to resemble a bishop's mitre. A replacement, the US 105 Millimeter Howitzer Motor Carriage M7 was called "Priest" by the British, as part of its superstructure was said to resemble a priest's pulpit. Following this line of names, a 1942 self-propelled gun armed with the QF 6 pounder was "Deacon", a 1943 carrier weapon with the QF 25-pounder was "Sexton"; this practice was continued after the war with "FV433 Abbot SPG" and ended in 1993 with the introduction of the AS-90. Chris Henry, Mike Fuller - The 25-pounder Field Gun 1939-72, Osprey Publishing 2002, ISBN 1-84176-350-0. Trewhitt, Philip. Armored Fighting Vehicles. New York, NY: Amber Books. P. 114. ISBN 0-7607-1260-3. Flames of War: Bishop, 8th Army World War II Vehicles
Bren light machine gun
The Bren gun called the Bren, are a series of light machine guns made by Britain in the 1930s and used in various roles until 1992. While best known for its role as the British and Commonwealth forces' primary infantry LMG in World War II, it was used in the Korean War and saw service throughout the latter half of the 20th century, including the 1982 Falklands War. Although fitted with a bipod, it could be mounted on a tripod or vehicle-mounted; the Bren was a licensed version of the Czechoslovak ZGB 33 light machine gun which, in turn, was a modified version of the ZB vz. 26, which British Army officials had tested during a firearms service competition in the 1930s. The Bren featured a distinctive top-mounted curved box magazine, conical flash hider, quick change barrel; the name Bren was derived from Brno, the Czechoslovak city in Moravia, where the Zb vz. 26 was designed and Enfield, site of the British Royal Small Arms Factory. The designer was a gun inventor and design engineer. In the 1950s, many Brens were re-barrelled to accept the 7.62×51mm NATO cartridge and modified to feed from the magazine for the L1 rifle as the L4 light machine gun.
It was replaced in the British Army as the section LMG by the L7 general-purpose machine gun, a heavier belt-fed weapon. This was supplemented in the 1980s by the L86 Light Support Weapon firing the 5.56×45mm NATO round, leaving the Bren in use only as a pintle mount on some vehicles. The Bren is still manufactured by Indian Ordnance Factories as the "Gun, Machine 7.62mm 1B". At the close of the First World War in 1918, the British Army was equipped with two main automatic weapons; the Vickers was heavy and required a supply of water to keep it in operation, which tended to relegate it to static defence and indirect fire support. The Lewis, although lighter, was prone to frequent stoppages. In 1922, the Small Arms Committee of the British Army ran competitive trials to find replacement for the Lewis, between the Madsen, the Browning Automatic Rifle, the Hotchkiss, the Beardmore-Farquhar and the Lewis itself. Although the BAR was recommended, the sheer number of Lewis guns available and the difficult financial conditions meant that nothing was done.
Various new models of light machine gun were tested as they became available, in 1930, a further set of extensive trials commenced, overseen by Frederick Hubert Vinden. This time the weapons tested included the SIG Neuhausen KE7, the Vickers-Berthier and the Czechoslovak ZB vz.26. The Vickers-Berthier was adopted by the Indian Army because it could be manufactured at once, rather than wait for the British Lewis production run to finish. Following these trials, the British Army adopted the Czechoslovak ZB vz.26 light machine gun manufactured in Brno in 1935, although a modified model, the ZB vz. 27, rather than the ZB vz. 26, submitted for the trials. The design was modified to British requirements under new designation ZGB 33, licensed for British manufacture under the Bren name; the major changes were in the magazine and barrel and the lower pistol grip assembly which went from a swiveling grip frame pivoted on the front of the trigger guard to a sliding grip frame which included the forward tripod mount and sliding ejection port cover.
The magazine was curved in order to feed the rimmed.303 SAA cartridge, a change from the various rimless Mauser-design cartridges such as the 8mm Mauser round used by Czech designs. These modifications were categorised in ZB vz. 27, ZB vz. 30, ZB vz. 32, the ZGB 33, licensed for manufacture under the Bren name. The Bren was a gas-operated weapon, which used the same.303 ammunition as the standard British bolt-action rifle, the Lee–Enfield, firing at a rate of between 480 and 540 rounds per minute, depending on the model. Propellant gases vented from a port towards the muzzle end of the barrel through a regulator with four quick-adjustment apertures of different sizes, intended to tailor the gas volume to different ambient temperatures; the vented gas drove a piston. Each gun came with a spare barrel that could be changed when the barrel became hot during sustained fire, though guns featured a chrome-lined barrel, which reduced the need for a spare. To change barrels, the release catch in front of the magazine was rotated to unlock the barrel.
The carrying handle above the barrel was used to grip and remove the hot barrel without burning the hands. The Bren was magazine-fed, which slowed its rate of fire and required more frequent reloading than British belt-fed machine guns such as the larger.303 Vickers machine gun. The slower rate of fire prevented more rapid overheating of the Bren's air-cooled barrel, the Bren was much lighter than belt-fed machine guns, which had cooling jackets liquid filled; the magazines prevented the ammunition from getting dirty, more of a problem with the Vickers with its 250-round canvas belts. The sights were offset to the left; the position of the sights meant. In the British and Commonwealth armies, the Bren was issued on a scale of