M203

The M203 is a single shot grenade launcher attachment that is featured in Call of Duty 4: Modern Warfare, Call of Duty: Modern Warfare 2, and Call of Duty: Black Ops.

Call of Duty 4: Modern Warfare
In Call of Duty 4: Modern Warfare's multiplayer mode, all assault rifles except for the MP44 and AK-47 can be outfitted with an M203. The AK-47 uses the GP-25 Grenade Launcher, and the MP44 cannot equip attachments. The grenades it shoots are slightly weaker than fragmentation grenades, but they are also extremely accurate, fast-moving, and have very little arc. Also, it does not need to be unlocked through challenges. For these reasons, it is generally looked down upon as unfair by many players when used in multiplayer. This attachment replaces Perk 1 in multiplayer. Even though leaf sights are present on both the M4A1 and the M16A4 when the M203 is attached they are never used. Most likely this is to not unbalance the accuracy between M203s with iron sights and M203s without.

If the Overkill perk is used and both selected weapons have the M203 (or the GP-25) grenade launcher, then the player will have 4 40mm grenades (1 in each launcher and 2 spare ones for reloads), except in the Wii version, which sets it at only 3. Since the M203 is a weapon attachment, players cannot pick up more ammo for it by walking over a dropped gun with a grenade launcher attached (unless they currently have the empty attachment up while doing so, prompting a reload). It can be difficult to gain more ammo for the M203 without respawning.

Call of Duty: Modern Warfare 2
The M203 returns in Modern Warfare 2. It is mostly the same as in Call of Duty 4, except it sounds slightly less tubey. In multiplayer, it is mostly the same except now it does not take up a Tier 1 slot, unlike in Call of Duty 4. Sleight of Hand affects the reload speed, effectively increasing its rate of fire. With the introduction of the Scavenger or One Man Army perk, one can technically acquire infinite numbers of grenades. It is notable that if the player is at maximum ammo with the rest of their weapons and grenades (common when using Scavenger Pro), they must have the grenade launcher equipped to pickup more ammo with Scavenger. This can make picking up replacement grenades in combat troublesome if the player uses their grenade launcher first or exclusively. It is commonly seen used in conjunction with the perks Danger Close and One Man Army, however, it is highly frowned upon by many players, as it requires simple point and shoot to get a Grenade Launcher kill, and One Man Army means that the player can simply keep on infinitely reloading their Grenade launcher attachment.

Singleplayer
The grenade launcher is set to return in Call of Duty: Black Ops. It is seen mounted on the Commando assault rifle and has a very similar reload animation and the same aiming system as the Modern Warfare games. Unlike the M203 in the Modern Warfare series, the M203 creates the same firing sound as the Rifle Grenade Launcher in Call of Duty: World at War, though this may have been a placeholder. It was seen in the E3 demo of the game. The level that had the grenade launcher was "Payback".

Multiplayer
Due to the grenade launcher being frowned upon by many players, the attachment will cost 3000 CoD Points and cannot be used with the perk Warlord. Also, its grenades will not be replenished by the Scavenger perk. There are also no explosive damage increasing perks like Danger Close, Fireworks, or Sonic Boom.

The perk will also take the tier one slot like in CoD4 and WaW to balance it.

Call of Duty: Black Ops DS
The M203 appears in a screen-shot of Black Ops DS, attached to an AK-47. It is unknown whether it will be an attachment for all assault rifles or be exclusive to the AK-47.

Trivia

 * In the console multiplayer mode of Modern Warfare 2, the M203 is accompanied by a vibration in the controllers when fired. However, in Single Player, only the M4A1 and the M16A4 has the vibration effect while other grenade launcher-capable rifles do not.
 * In campaign, when the M203 is attached to weapons like the M4A1 and the SCAR-H it can hold a total of 11 grenades, but when attached to the M16A4 the player can only hold a total of 4 grenades. This is more than likely an oversight.
 * When using the Infinite Ammo cheat in Call of Duty 4, the M203 attached to the M16A4 fires much faster than it does on other weapons. This is also true in the multiplayer.
 * In Modern Warfare 2's Singleplayer, the M203 makes quick work on large groups or riot shielded enemies when fired to the side or behind them.
 * The challenge "Ouch" is completed when the player fires a grenade into an opponent without setting the explosion off.
 * When firing either of the two under-barrel grenade launchers, the M203 or GP-25, the muzzle blast comes from the rifle barrel, not the grenade launcher's barrel.
 * On the Wii version of Call of Duty 4: Modern Warfare, the reticule for the grenade launcher is different, looking similar to the Holographic Sight.
 * It is possible to get a headshot with the M203 Grenade Launcher.
 * The M203 reloads slightly faster than its GP-25 counterpart. This is balanced by the GP-25's quicker switch speed.
 * It is possible to get a double kill or even a Triple with the M203 without detonation. It must bounce off one foe and onto another. This, of course, can also be performed with the GP-25 and the Thumper which makes sense because they all fire a grenade.
 * The M203 is often referred to as the "Noob Tube" by players who dislike the attachment, as it can be used to easily achieve kills with little effort or skill. This term comes from the grenade launcher resembling a tube, and the word "noob" is a derogatory term used to refer to less experienced players. This term can also apply to the AT4, Thumper and RPG-7, as these can be used in the same manner.
 * The M203 is used on every assault rifle except the AK-47, which uses the GP-25, and the MP44, which has no attachments.
 * In third person, when the M203 is equipped, the wielder's hand will go through the M203 body.
 * The M203 in Call of Duty 4: Modern Warfare and Call of Duty: Modern Warfare 2 is missing the trigger guard, probably for faster weapon cycling.