Besa machine gun

The Besa Machine Gun was a British version of the Czechoslovak ZB-53 air-cooled, belt-fed machine-gun, which in the Czechoslovak army was marked as the TK vz. 37. It was used extensively by the armed forces of United Kingdom during the Second World War, as a mounted machine gun for tanks and other armoured vehicles, to replace the heavier, water-cooled Vickers machine gun. Although it required a rather large opening in the tank's armour, it was dependable and reliable. The name came from the Birmingham Small Arms Company (BSA), who signed an agreement with Československá zbrojovka to manufacture the gun in the UK. The War Office ordered the weapon in 1938, and production began in 1939, after modifications.

Development and use
Although Britain's armed forces used the .303 in rimmed round for rifles and machine guns, the ZB-53 had been designed for the German 7.92 x 57mm Mauser round - referred to by the British as the 7.92mm. Although it had been intended for the British to move from rimmed to rimless ammunition generally, with war imminent wholesale change was not possible. It was considered by BSA and the Ministry of Supply that the industrial, technical, and logistical handicap of converting the design to the .303 round was more onerous than retaining the original calibre, especially given that the chain of supply for the Royal Armoured Corps was already separate from the other fighting arms of the British Army. As a consequence, the round was not changed for British production. Since the Besa used the same ammunition as Germany used in its rifles and machine guns, the British could use stocks of captured enemy ammunition.

The Mark II version entered production in 1940. It was modified with a selector to give high (around 800 rounds per minute) or low (around 500) rates of fire. As the war progressed the design was modified to be more rapidly and economically produced, resulting in the Mark III version. This came as either an "L" (for low) or "H" (high) firing rate models. While American-produced armoured cars or tanks would have been fitted with .30 cal Browning machine guns, many British tanks and armoured cars would be equipped with the Besa machine gun.

15 mm BESA
A larger, heavier - at 57 kg (125 lb) - 15 mm version, also belt-fed, was developed by BSA from the Czechoslovak ZB vz.60 heavy machine-gun as vehicle armament. It could be fired in semi-automatic mode as well as fully automatic. It was used on the Light Tank Mk VIC and on armoured cars such as the Humber Armoured Car Mark III. 3218 15mm BESA were manufactured until it was declared obsolete in 1949. It fired a 15 x 104 mm cartridge with a 75 grams bullet with a speed of 900 m/s. A few of the original ZB-60 guns were also used by the SS although mostly with the ammunition of the MG 151/15, which was slightly shorter having a case length of only 101 mm.