The M203 was designed and procured as the replacement for the M79 grenade launcher of the Vietnam era.
The M203 40mm Grenade Launcher is used while attached to an M16A2 5.56mm rifle. It is a lightweight, compact, breech loading, pump action, single shot launcher. The launcher consists of a hand guard and sight assembly with an adjustable metallic folding, short-range blade sight assembly, and an aluminum receiver assembly which houses the barrel latch, barrel stop and firing mechanism. The launcher is capable of firing a variety of low velocity 40mm ammunition.
The launcher also has a quadrant sight which may be attached to the M16A2 carrying handle and is used when precision is required out to the maximum effective range of the weapon.