In this picture diagram, it shows the method of operation or the Bren gun; the firing and recoil mechanism is also illustrated in the inset diagram. The spring-loaded magazine A containing 30 rounds is clipped on to the gun by means of securing-catch B. The back sight C is adjusted by wheel D, with fore sight E. Gun is then ready for action. Trigger F has been pressed. This has caused sear G to release slide H which under pressure from recoil spring J at the base of push-rod K has moved forward. In moving forward the bolt L strips a cartridge from the magazine into its firing position M. This ends the forward movement and the slide is locked... The bolt hammer N then strikes the firing pin and bullet flies along rifled bore. As it passes gas block P some of the expanding gases are diverted through gas regulator Q (size of gas opening regulates speed of fire) and, gas vent R into gas cylinder S. This forces piston T back, unlocking bolt. The slide then opens breech, extracts spent-cartridge, which is drawn back and strikes ejector U and drops through a hole in base of gun V. The piston and slide still drive back, compressing the recoil spring. When the spring expands again it restarts the whole cycle, and continues as long as the trigger is depressed and,until the magazine is empty. W shows a crew using a gun on tripod mounting and in the background are caterpillar driven Bren gun-carriers. To eliminate jamming through overheating a spare barrel X is provided, the barrels, being changed by means of carrying handle Y. To the enormous fire power of the British Infantry the biggest contribution in 1939 was made not as in 1914 by the rifle, but by the Bren Gun, with which every battalion was equipped. Originally designed and manufactured in Czechoslovakia the gun gets its name from the town of Bren, or Brno in Moravia, the Bren was turned out in huge quantities on mass production lines at ordnance factories in Britain, although the later model was more elaborate and even more effective than that which was produced at the famous Skoda works. Simple to operate and most deadly in effect, the Bren, was an exceedingly complicated piece of machinery, consisting of 172 parts, in whose making 3,000 separate operations were involved. Supreme among the advantages of the Bren gun is its adaptability to all the changes and chances of Wartime day. Here we see it mounted on a tripod ready to engage enemy aircraft. The man on the right has a second magazine in readiness. The Bren gun was 45 inches in length, weighed 21 lb, and was gas operated, gas from the first explosion fired the next round, and so on, and its potential firing was 500 rounds of 303 ammunition per minute. The actual fire, allowing time for changing the magazine was 120 per minute. The gun could be regulated to give four speeds in either single or multiple shots. Another feature in its favour was its extreme mobility, as it could be mounted either on a tripod or a bipod, or fired direct from the shoulder.