M203 40-mm Grenade Launcher
The M203 was designed to replace the M79 grenade launcher that had been used successfully in Vietnam. It attaches below the M16A1 or M16A2. To load, the barrel release is depressed and the barrel is pushed forward, the round loaded, and the barrel pulled back to a locking position. It has its own trigger and safety.
Although the M203 has sights, you quickly get the feel of it and can accurately fire it without use of the sights. In Ranger squads, there are typically two grenadiers, one on A-team and one on B-team.