M203

The M203 is a single shot 40mm grenade launcher that can be attached to a variety of weapons. It is currently in use with the US military, though it is in the process of being replaced with the Heckler & Koch M320 Grenade Launcher Module (GLM).

The AK-47 uses the GP-25 Grenade Launcher.

In Game
In Call of Duty 4: Modern Warfare, assault rifles can be outfitted with a M203 grenade launcher (the StG44 is the only exception). No challenges need to be completed to unlock this attachment. Attaching a grenade launcher to an AK-47 will result in the grenade launcher being renamed, and will have a different reload animation. The AK-47's grenade launcher is named the GP-25, which is the only different grenade launcher other than the M203 that is used on Call of Duty 4. However, the G3 and G36C are not compatible with the M203 Grenade Launcher in reality. Selecting the M203 as an attachment will void the use of a perk for perk 1. In Call of Duty 4 multiplayer, the grenade launcher is often referred to as the "Noob Tube," because of it's availability from the start and the fact that it requires little to no skill to use.

Enemies who are hit by the grenade or are near the point of detonation will be killed; enemies beyond a certain distance of the point of detonation will be injured. However, the grenade must travel a certain distance after being fired to become armed, or it will not detonate on impact. However, an enemy hit with the grenade that is not armed will be killed. Players carrying one M203 are given two grenades to use, while players using two weapons with mounted M203s (through the use of Overkill) have either three grenades in one M203 and one in the other (this occurs if both guns use the same ammo, such the G36C, M4, and M16 or G3 and M14) - or 2 in both.