The Mk 19 (or Mark 19) is a grenade machine gun capable of firing one grenade every second at a maximum range of . The Mk 19 fires 40mm grenades at a rate of 325-375 rounds per minute (rpm). It has a maximum effective range of . It was originally used by the U.S. Navy in Vietnam for river patrol boats. Later it was adopted and improved upon by the U.S. Army. It is a man portable crew-served weapon that can fire from a mounted position. It also fires from a vehicle mounted position (this is the preferred method since the weapon alone weighs ). The ammunition comes in 32 or 48 round ammunition boxes weighing and .