XM174 40mm grenade launcher
These units were adopted by the Air Force, US Army and the USMC and did suffer from a number of various issues but by 1968 the Naval Ordnance Station in Louisville had developed the MK19…which was quickly adopted by the US and the Marines for use on vechiles and tripod mounts.
Quickly thereafter the Ordnance Corps abandoned the XM174E1 for the MK19 grenade launcher