Bren Light Machine Gun - Development

Development

During the early 1930s, the British Army subjected several designs of light machine gun to competitive trials. Among the weapons that were submitted for the trials were the Madsen, Browning Automatic Rifle (BAR), the Neuhausen KE7 and the Vickers-Berthier. The Vickers-Berthier was later adopted by the Indian Army and also saw extensive service in World War II.

Following these trials, the British Army adopted the Czechoslovak ZB vz.26 light machine gun manufactured in Brno in 1935, although a slightly modified model the ZB vz. 27 rather than the ZB vz. 26 had actually been submitted for the trials. A licence to manufacture was sought, and the Czech design was modified to British requirements. The major changes were in the magazine and barrel. The magazine was curved in order to feed the rimmed .303 British cartridge, a change from the various rimless Mauser-design cartridges such as the 7.92 mm Mauser round previously used by Czech designs. These modifications were categorised in various numbered designations, ZB vz. 27, ZB vz. 30, ZB vz. 32, and finally the ZB vz. 33, which became the Bren.

The Bren was a gas-operated weapon, which used the same .303 ammunition as the standard British rifle, the Lee-Enfield, firing at a rate of between 480 and 540 rounds per minute (rpm), depending on model. Propellant gases vented from a port towards the muzzle end of the barrel through a regulator (visible in the photo, just in front of the bipod) with four quick-adjustment apertures of different sizes, intended to tailor the gas volume to different ambient temperatures (smallest flow at high temperature, e.g. summer desert, largest at low temperature, e.g. winter Arctic). The vented gas drove a piston which in turn actuated the breech block. Each gun came with a spare barrel that could be quickly changed when the barrel became hot during sustained fire, though later 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 risk of 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. However, the slower rate of fire prevented more rapid overheating of the Bren's air-cooled barrel, and the Bren was several pounds lighter than belt-fed machine guns which typically had cooling jackets, often liquid filled. The magazines also prevented the ammunition from getting dirty, which was more of a problem with the Vickers with its 250-round canvas belts.