Considered the world's first genuine sub-machine gun, the Villar Perosa (or VP) was introduced in the Italian army in 1915.

Used as an infantry weapon, the Villar Perosa utilised a nickel and steel twin-barrel mechanism, each of which fired a 25-round box magazine of 9mm Glisenti pistol ammunition - essentially a low powered 9mm Parabellum cartridge.

A rapid-firing device - it could fire 300 rounds per minute per barrel, requiring that it be recharged up to twelve times per minute - it was nevertheless chiefly used in support positions until 1918, when a modified Beretta version of the weapon was unveiled in the autumn.

It was thereafter deployed as an infantry assault weapon, although there is some dispute regarding the actual extent of its use.  Its theoretical range was 800 metres although in practice it was around 100 metres - which rendered reloading a perilous operation.