Originally designed for aircraft use, this particular Italian Villar Perosa dual SMG was adapted for ground use. It consists of two separate submachine guns joined together. The spade grip has two thumb triggers which you can use to fire each of the SMGs separately or push them simultaneously to fire both.
Each of the guns is fed from its own top-mounted magazine and must be charged separately. The Villar Perosa is chambered in 9mm Glisenti which is dimensionally identical to the 9x19mm but it was loaded to weaker pressure levels.