The FMK-3 submachine gun was developed by Fabricaciones Militares company of Argentina circa 1974 and is being manufactured by Small Arms factory of Domingo Matheu. It is used by Army and Police of Argentina, and also, in semi-automatic version is sold to civilians under the name of FMK-5.

FMK-3 is a blowback-operated, selective fire submachine gun. It uses telescoped bolt, that sleeves around the rear part of the barrel when closed. Double stak magazine is inserted into the pistol grip. Receiver and pistol grip is made from steel stampings, safety/fire selector switch is located at the left side of the weapon above the pistol grip. There also is an automated grip safety at the rear of the pistol grip. The sights are of flip-up type with "L"-shaped rear sight blade, marked for range of 50 and 100 meters. The retractable buttstock is made from steel wire.