"The Thumper is a favorite among our troops. Simple, reliable, and powerful, it significantly improved the firepower potential of our unit. Some troops were so skilled at its use that they could lob a grenade into an open window 200 meters away."
-Lt. Michael Morita, Paternian Army, 101st Airborne Regiment

The M79 is an American 40mm single-shot, break-action grenade launcher. It was designed to have greater accuracy and range than a rifle grenade, but greater portability than a mortar. To achieve this, it employed the high-low system that incorporated a small high pressure chamber and a large low pressure chamber. The high-pressure chamber contained the propellant. When fired, gases from the high-pressure chamber bleed into the low-pressure chamber, providing thrust to the projectile. This allows for a relatively large caliber weapon with low recoil,and lighter weight with efficient use of propellant. Developed by Germany towards the end of World War II, it saw very limited use before the M79 and its 40x46mm grenade was adopted.

The weapon was known by a variety of names due to its distinct report, such as "Thumper", "Blooper", "Thump-gun", and "Bloop-tube". In Australian service, it was known as the "Wombat Gun". The weapon was very versatile, able to fire anti-personnel, smoke, buckshot, flechette, and illumination rounds.

While largely replaced by the underbarrel M203 by the end of the Vietnam War, it remains useful in some units for its longer range and greater accuracy over the M203 as well as its ability to fire less-lethal crowd control ammunition.