The Mk 19 is an late Cold War era automatic grenade launcher of US origin. It was designed in the mid-1960's and was extensively used during the late stages of the Vietnam war. The Mk 19 was the first automatic grenade launcher designed for ground use. In the USA it is designated as a grenade machine gun.

The Mk 19 is a blowback operated weapon that fires the same high velocity 40mm grenades as used in the earlier M75. The belts are fed from left to right and are usually held in a box attached to the left of the weapon. Early weapons used advanced primer ignition and were found to have limited reliability. Following over a decade of improvements the design settled on the Mk 19 MOD 3 which uses a straigh blowback operation. The Mk 19 is aimed and fired using the spade grips at the rear. Iron sights are mounted on top of the weapon.

The Mk 19 fires 40x53mm high velocity grenades from 32 or 48 round belts. A variety of grenade types is available. The standard HEDP grenades have a lethal radius of 5 m, wounding radius of 15 m and will pierce the armor of most armored vehicles. The cyclic rate of fire is 325 to 375 rpm. The practical rate of fire is 60 rounds in one minute or 40 rpm during sustain fire. The maximum range is 2 km, although the sight are gradated only to 1.500 yards. The GMG is reported to be so accurate that grenades can be launched though an individual window at a distance of over 1 km.

The main user of the Mk 19 is the United States military. It was extensively used during the late stages of the Vietnam war and all subsequent conflicts. It is sometimes used on a tripod, but is mostly vehicle mounted due to its weight. The Mk 19 was also very succesful as an export product with only the Soviet AGS-17 in more widespread use.