The 40mm, Y2 MK-1 Six Shot Grenade Launcher is a lightweight, semi-automatic, shoulder fired grenade launcher for infantry use. It fires the widely used 40mm, low velocity family of grenades. The weapon is based on the revolver principle with a cylinder holding six rounds. A gas piston activates the cylinder, which is spring driven. The 40mm, Y2 MK-1 Grenade Launcher is fitted with an Occluded Eye Gun-sight (OEG), which means that the weapon is fired with both eyes open. The sight is operational in poor light conditions as long as the target can be seen.