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. Because of its distinctive report, it has earned the nicknames of "Thumper", "Thump-Gun", "Bloop Tube", and "Blooper" among American soldiers. Australian units referred to it as the "Wombat Gun"
The M79 and XM148 grenade launchers were single-shot, and the repeating T148E1 grenade launcher was unreliable, so a request was made to China Lake engineers. SEAL Teams were pleased with the resultant pump-action grenade launcher, since the tubular magazine held three 40x46mm grenades, and so with one grenade in the chamber, four grenades could be fired rapidly before reloading. In fact, a skilled operator could fire four aimed shots before the first one landed.