The Ultimax 100 is a Singapore-made 5.56mm light machine gun, developed by the Chartered Industries of Singapore (CIS, now ST Kinetics) by a team of engineers under the guidance of American firearms designer L. James Sullivan. The weapon is extremely accurate due to its constant-recoil operating system and is one of the lightest machine guns in the world. Work on a new light support weapon for the Singapore Army began in 1978. The weapon is produced by CIS (presently STK—Singapore Technologies Kinetics), initially in the Mark 1 version, later—the Mark 2, and currently, in the Mark 3 and Mark 4 variant. The Ultimax 100 (also called the U 100) is used in significant numbers by the armed forces of Singapore, Croatia and the Philippines. The Mark 3 variant is currently used in the Singapore Armed Forces primarily as a support arm, and is both classified and known by soldiers as the SAW (Section Assault Weapon). Design details The Ultimax 100 is a gas-operated automatic weapon (capable of fully automatic fire only) with a short-stroke gas piston operating system powered by ignited powder gases diverted from the barrel through a port in the gas block. The Ultimax 100 is a locked breech weapon with a rotating bolt that contains 7 locking lugs. It fires from an open bolt position. The bolt contains both a spring extractor and a casing ejector. The weapon's non-reciprocating cocking handle is located on the left side of the receiver and occupies the forward position during firing. The Ultimax 100 is striker-fired. The feature that grants the weapon its low recoil (compared to similar light machine guns) is the "constant recoil" principle. The overall design allows the bolt carrier group to travel all the way back without ever impacting the rear, instead stopping gradually along the axis of movement against the resistance of the return springs. Jane's International Defence Review correspondent — Andrew Tillman, in an exclusive invitation from ST Kinetics to participate in the Product Improvement Program (PIP, initiated in 1989) to test fire the gun, elaborated: The magazine catch consists of two tapered pins on a bar, controlled by the magazine release button. The machine gun feeds from a proprietary 100-round synthetic drum magazine (early models also used 60-round drum magazines), or from a modified 20 or 30-round STANAG 4179 magazine (from the M16 rifle). An unusual feature among modern machine guns is the fact