Second World War
In the British and Commonwealth armies, the Bren was generally issued on a scale of one per rifle section, with three rifle sections in each platoon. A further three Bren guns were issued to the Admin platoon of each rifle company. An infantry battalion also had a "carrier" platoon, equipped with Universal Carriers, most of which carried Bren guns. Parachute battalions from 1944 had an extra Bren in the AT platoon. The 66-man "Assault Troop" of British Commandos had a nominal establishment of four Bren guns. Realising the need for additional section-level firepower, the British Army endeavoured to issue the Bren in great numbers, with a stated goal of one Bren to every four private soldiers.
The Bren was operated by a two-man crew, sometimes commanded by a Lance Corporal as an infantry section's "gun group", the remainder of the section forming the "rifle group". The gunner or "Number 1" carried and fired the Bren, and a loader or "Number 2" carried extra magazines, a spare barrel and a tool kit. Number 2 helped reload the gun and replace the barrel when it overheated, and spotted targets for Number 1.
Generally, the Bren was fired from the prone position using the attached bipod. On occasion, a Bren gunner would use his weapon on the move supported by a sling, much like an automatic rifle, and from standing or kneeling positions. Using the sling, Australian soldiers regularly fired the Bren from the hip, for instance in the marching fire tactic, a form of suppressive fire moving forward in assault. A Victoria Cross was awarded to Private Bruce Kingsbury for such use at Isurava, New Guinea in 1942, during the Australians' fighting retreat from Kokoda.
Each British soldier's equipment normally included two magazines for his section's Bren gun. The large ammunition pouches on the 1937 Pattern Web Equipment were designed around the Bren magazine. Every soldier would be trained to fire the Bren in case of an emergency, though these soldiers did not receive a Bren proficiency badge.
The Bren had an effective range of around 600 yards (550 m) when fired from a prone position with a bipod. Initial versions of the weapon were sometimes considered too accurate because the cone or pattern of fire was extremely concentrated. Soldiers often expressed a preference for worn-out barrels in order to spread the cone of fire and increase suppressive effects. Later versions of the Bren addressed this issue by providing a wider cone of fire.
For a light machine gun of the interwar and early World War II era, the Bren was about average in weight. On long marches in non-operational areas it was often partially disassembled and its parts were carried by two soldiers. The top-mounted magazine vibrated and moved during fire, making the weapon more visible in combat, and many Bren gunners used paint or improvised canvas covers to disguise the prominent magazine.
The 30-round magazine was in practice usually filled with 27 or 28 rounds to prevent jams and avoid wearing out the magazine spring. Care needed to be taken when loading the magazine to ensure that each round went ahead of the previous round, so that the .303 cartridge rims did not overlap the wrong way, which would cause a jam. The spent cartridge cases were ejected downwards, which was an improvement on the Lewis gun which ejected sideways, since the glint of them flying through the air could compromise a concealed firing position.
In general, the Bren was considered a reliable and effective light machine gun, though in North Africa it was reported to jam regularly unless kept very clean and free of sand or dirt. It was popular with British troops, who respected the Bren for its reliability and combat effectiveness. The quality of the materials used would generally ensure minimal jamming. When the gun did jam through fouling caused by prolonged firing, the operator could adjust the four-position gas regulator to feed more gas to the piston increasing the power to operate the mechanism. The barrel needed to be unlocked and slid forward slightly to allow the regulator to be turned. It was even said that all problems with the Bren could simply be cleared by hitting the gun, turning the regulator, or doing both.
A complicated tripod mount was available to allow the Bren to be used as an indirect-fire weapon, but this was rarely used in the field. The Bren was also used on many vehicles, including on Universal Carriers, to which it gave the alternative name "Bren Gun Carrier", and on tanks and armoured cars. However, it could not be used as a co-axial weapon on tanks, as the magazine restricted its depression and was awkward to handle in confined spaces, and it was therefore used on a pintle mount only. (The belt fed Vickers or BESA, the latter being another Czechoslovak machine gun design adopted by the British, were instead used as co-axial weapons.) An unfortunate problem occurred when the Bren was fired from the Dingo Scout Car; the hot cartridge cases tended to be ejected down the neck of the driver, whose position was right next to the pintle. A canvas bag was designed to catch the cartridges and overcome the problem, but it seems to have been rarely issued.
The Bren was also employed in the anti-aircraft role. A tall tripod was available to allow high angle fire. There were also several designs of less portable mountings, including the Gallows and Motley mounts. A 100-round pan magazine was available for the Bren for use in the anti-aircraft role.
The Bren's direct ancestor, the Czechoslovak ZB vz. 26, was also used in World War 2 by German and Romanian forces, including units of the Waffen SS. Many 7.92 mm ZB light machine guns were shipped to China, where they were employed first against the Japanese in World War II, and later against UN forces in Korea, including British and Commonwealth units. Some ex-Chinese Czech ZB weapons were also in use in the early stages of the Vietnam War.
Production of a 7.92 mm round model for the Far East was carried out by Inglis of Canada.
The Bren was also delivered to the Soviet Union as part of the lend-lease program
The British Army, and the armies of various countries of the Commonwealth, used the Bren in the Korean War, the Malayan Emergency, the Mau Mau Uprising and the Indonesia–Malaysia confrontation, where it was preferred to its replacement, the belt-fed GPMG, on account of its lighter weight. During the Falklands War in 1982, 40 Commando Royal Marines carried one LMG and one GPMG per section.
When the British Army adopted the 7.62 mm NATO cartridge, the Bren was re-designed to 7.62 mm calibre, fitted with a new bolt, barrel and magazine. It was redesignated as the L4 Light Machine Gun (in various sub-versions) and remained in British Army service into the 1990s. A slotted flash hider similar to that of the contemporary L1 rifle and L7 General Purpose Machine Gun replaced the conical flash hider. The change from a rimmed to rimless cartridge and nearly straight magazine improved feeding considerably, and allowed use of 20-round magazines from the 7.62 mm L1A1 Self-Loading Rifle. The 30-round magazine from the L4 also fitted the L1A1 rifle, but the magazine spring was not always strong enough to provide enough upward pressure to feed rounds correctly, this being remedied by stretching the magazine springs.
Completion of the move to a 5.56 mm NATO cartridge led to Army removing the Bren/L4 from the list of approved weapons and then withdrawing it from service. The fact that Bren guns had remained in service for so many years with so many different countries in so many wars says much about the quality of the weapon's design.
The Mark III Bren remained in limited use with the Army Reserve of the Irish Defence Forces until 2006, when the 7.62 mm GPMG replaced it. The Bren was popular with the soldiers who fired it (known as Brenners) as it was light and durable, and had a reputation for accuracy. The most notable use of the Bren by Irish forces was in the Congo Crisis during the 1960s, when the Bren was the regular army's standard section automatic weapon.