The XM174 is a mounted automatic 40mm grenade launcher heavily based on the M1919A4 machine gun and the M79 grenade launcher but fed from an ammo can. It was used in the Vietnam War as a tripod mounted crew-served weapon and as a weapon mounted on various vehicles and aircraft.

The ammunition canister held 12 40mm rounds, and the automatic launcher's rate of fire permitted all 12 rounds to be in the air before the first round landed. The launcher was also capable of semi-automatic fire (one round per pull of the trigger).