The X4 was an Italian submachine gun designed by Fabrica Nazionale d’Armie Brescia in 1954.
FNA-B marketed the X4 in 1954, and the shortened X5 model a year later. Both guns were extremely cheap to produce and cost-efficient, and FNA-B planned a production run of 100,000 models. However, with no orders for the weapon, the gun ultimately never entered mass production and only a limited number were ever made.
The X5 model was, at the time of its design, one of the shortest submachine guns available.
Both the X4 and the X5 were constructed almost entirely from stamped sheet metal. The bolt was cylindrical with a fixed firing pin and the cocking handle was attached to a sleeve that wrapped around the entire bolt. The magazine housing was especially deep. Only fully-automatic fire was possible. The X4 utilized a retractable wire stock, but the X5 did not.