The Mk 19 grenade launcher (also known as the Mark 19) is an American 40mm belt-fed automatic grenade launcher that was first developed during the Vietnam War. The first model (Mod 0) in 1966 was determined to be unreliable and unsafe, but a total of 6 Mod 1 launchers were successfully tested on U.S. Navy riverine patrol craft in the Mekong Delta in 1972. The Navy made further improvements to the weapon, resulting in the Mod 3 in 1976. The MOD 3 was adopted by the U.S Army in 1983 and remains in service to the present day.