Task: Question Generation
Input (English): Context : The M79 grenade launcher is a single-shot, shoulder-fired, break-action grenade launcher that fires a 40×46mm grenade, which uses what the US Army calls the High-Low Propulsion System to keep recoil forces low, and first appeared during the Vietnam War. 
Subject : M79 grenade launcher 
Relation : service entry
Output (English): What year was M79 grenade launcher made?