The Beretta M1918 was one of two simultaneous efforts to turn the M1915 Villar-Perosa machine gun into a more practical weapon. The Officine Villar Perosa (who had manufactured the 1915 gun in the first place) did one version, and Beretta did the other. In fact, Beretta’s version was the work of none other than Tullio Marengoni – he would continue to work at Beretta for decades, and produce many of their most iconic pistol and submachine gun designs.
Anyway, both efforts were based on splitting the Villar Perosa into two separate receivers, and then designing a stock, sights, and trigger mechanism to make them viable shoulder weapons. The basic Villar Perosa action (open-bolt, slightly delayed blowback, 9mm Glisenti from 25-round top-mounted magazines) was kept intact, and one will recognize elements like the bolt handle, receiver end cap, and magazine catch from those original guns.
Beretta and Marengoni adapted a Carcano-style stock to the gun, and also fitted it with a folding cavalry-style spike bayonet. The version pictured here is actually a semi-automatic only carbine – a select-fire version was also made with what would become Beretta’s standard dual trigger FCG, as well as a single-trigger variant with a semi/full selector switch.
Reportedly 4000-5000 of these guns were delivered (of all varieties combined), and the stock of existing Villar-Perosa guns were broken up to provide the components for the M1918 guns (which helps explain why so few 1915 Villar Perosas survive today). These were introduced into service in 1918, and some sources suggest they actually saw service a few weeks before the first German MP-18 submachine guns, which would make them the first formal SMG used in combat. That exact point is disputed, but regardless they did see limited use right at the end of WWI, and continued in service through the end of WWII.
Courtesy of the National Firearms Centre in Leeds, we have a bunch of photos of an M1918 SMG: