Two Marines wearing the green dominant ERDL uniform and flak vests display their weapons. One holds an with the buttstock removed while the other Marine holds up an grenade launcher. Several and caliber ammunition cans are visible on the ground near them.
The M203 (dismounted here) is a single-shot 40 mm under-barrel grenade launcher designed to attach to a rifle. It uses the same rounds as the older stand-alone M79 break-action grenade launcher, which utilizes the High-Low Propulsion System to keep recoil forces low. Though versatile, and compatible with many rifle models, the M203 was originally designed for the U.S. M16 and its variant, the M4 Carbine.
As one of the best marksmen in my company, I was assigned this grenade launcher while serving with the Air Cavalry Division in Vietnam. It was not considered a great thing to have, as it made you something of a target for the enemy.