Villar Perosa aircraft submachine gun

The Villar Perosa M15 was an Italian portable automatic firearm developed during World War I by the "Officine di Villar Perosa".
Originally designed to be used by the second crew member/observer of military airplanes, it was later issued to ground troops. Between May and November 1916 a section was assigned to each infantry battalion of the Italian army and from May 1917 the number of sections was increased to 3 per battalion.
As it was designed to use 9mm pistol ammunition, it is said to be the first true submachine gun.
Design.
The Villar Perosa was designed as a portable double-barrel machine gun firing a 9mm round. It consisted of two independent coupled weapons, each with its own barrel, firing mechanism, and separate 25-round magazine.
As it was originally designed to be operated from airplanes, it had a high rate of fire of over 1,500 rounds per minute. However, in practice the 9mm munition was not sufficiently powerful to shoot down aircraft, which had become ever more resistant over the course of the war, and in addition the range was inadequate.
It was also used during World War I by the Italian infantry, with a bipod and a gun shield. Despite its high rate of fire, its atypical design, and its weight, it proved to be very effective at short range.
Legacy.
In 1918, Austria-Hungary created a copy of the VP, the Sturmpistole M.18, which featured a straight magazine rather than curved magazines.
The mechanism of the VP was a sound design, and shortly after the end of the war was used as the basis of a more practical weapon, the OVP submachine gun.