Grenade Launcher

A Grenade launcher is a device that shoots a grenade. These can be standalone launchers, such as the Thumper, or attachments to weapons, such as the M203. Grenade launchers appear in several forms throughout the Call of Duty series.

In Call of Duty 4: Modern Warfare, all assault rifles except the MP44 can have a Grenade Launcher attached, the M203 for most assault rifles and the GP-25 Kostyor for the AK-47. Call of Duty 3 and Call of Duty: World at War feature the Rifle Grenade which serve the same purpose. The GP-25 and M203 return in Call of Duty: Modern Warfare 2 for the AK-47 and all other assault rifles, respectively.

Singleplayer
The two grenade launchers available are the M203 and the GP-25, both of which can be found throughout the campaign.

The Mk 19 automatic grenade launcher is used in the mission Shock and Awe on the transport helicopter, and is used to lighten the ground resistance. It can destroy tanks in just a few shots.

Multiplayer
The Grenade Launcher is unique in that it is the only attachment that is unlocked without having to complete any challenges. The GP-25 functions the same as the M203 with only cosmetic differences. Using a grenade launcher takes up the first perk slot. Players can be killed either by the grenade's explosion or by being hit by the grenade directly. Enemies who are too far from the point of detonation will only be injured. The grenades are incredibly accurate and move quickly, but have a small blast radius. The grenade must travel a certain distance before it will explode, else it will only bounce off the surface it impacts. Players carrying a single grenade launcher will carry two grenades for it. Players carrying two weapons with a grenade launcher (using Overkill) will either have three for one and one for the other (if the two weapons use compatible ammo) or two for both.

Call of Duty: Modern Warfare 2
In Modern Warfare 2, the grenade launchers were largely left the same. There is, however, a new launcher, the Thumper, which is a very rare weapon in singleplayer.

Singleplayer
In singleplayer, grenade launchers are very common attachments. The only two assault-rifle mounted launchers available, again, are the M203 and the GP-25, the latter only seen on the AK-47.

The Thumper, which is a standalone weapon, is very rare to find in singleplayer. It is most notably found in the Spec Ops mission Wreckage.

Multiplayer
The grenade launchers were largely left the same in Modern Warfare 2, although using a launcher no longer uses a perk slot, but instead an attachment slot. It is impossible to use this with the shotgun attachment. Also, the grenade launcher requires completion of Marksman Rank 1 for most weapons before it can be used. Killing twenty enemies with the launcher unlocks the Masterkey Shotgun attachment for that weapon.

The most noticeable difference from Modern Warfare to Modern Warfare 2 is the GP-25's slightly faster swap-to time and slightly slower reload time, both of which are more exaggerated in the latter.

The Thumper is largely the same as the other launchers available, although it is a standalone secondary weapon. The primary difference between singleplayer and multiplayer Thumper is the ability to hip-fire is removed from multiplayer.

One frequently used, but heavily frowned upon, tactic with the Grenade Launcher is to use the One Man Army perk with an Assault Rifle with a Grenade Launcher attachment and switch to the same class to gain infinite grenades and combine that with the Danger Close Perk. Some players however use the Scavenger perk because it allows a Rocket Launcher to be equipped.

Trivia

 * A very easy way to complete the "The Survivor" challenge in Modern Warfare 2 is to fire a grenade (and purposefully miss) and immediately knife an opponent. With no ammo in the launcher, the game treats the player as "out of ammo".
 * If the player shoots a grenade at a nearby wall or something that it will bounce off of, they will be able to see the unexploded grenade on the ground. It is possible to cause an impact kill with the undetonated grenade by ricochet.
 * The Grenade Launcher (in all its forms, attachment or otherwise) is often called the "Noob Tube" by online players, due to its ease of use.
 * A grenade fired from the launcher that directly hits a player, provided they are close enough, will not explode, though it will still kill them.
 * Every grenade launcher has the same sound when fired. Even the Thumper has the same sound as every other grenade launcher.
 * In Modern Warfare, the extended mission of "F.N.G.", it was stated that the Grenade Launcher cancels out when fired too close for "safety" purposes.
 * All grenades fired by grenade launchers are modeled the same (in the Modern Warfare series). This can be observed by looking at grenades that didn't explode
 * In Modern Warfare 2, the player can complete a challenge called "Ouch" by killing someone with the grenade's direct impact. This will result in the title "Noob Tuber", a reference to players who excessively use grenade launchers.
 * When using Scavenger, the grenade has to be loaded to pick up another grenade. There are two slots for the grenade launcher: one that's loaded and one that is in reserve.
 * The grenade launcher attachment is often used with One Man Army to pick that same class to "refuel" their grenade supply.
 * It is possible to get a headshot with a grenade from a grenade launcher in Modern Warfare 2. However, the grenade must be "primed" in order to get a headshot. Hitting another player's head with a direct-impact will not yield a headshot kill.
 * It is easier to get a kill for the grenade launcher by shooting at the feet of an enemy player, if at long enough range it will explode killing the player, unless they have the Painkiller Death Streak.
 * The Modern Warfare 2 Create-a-Class picture lacks a trigger-guard.
 * If the 'Infinite Ammo' cheat is activated on Single Player (Modern Warfare only), then grenade launchers become fully automatic. The GP-25 will fire noticeably slower than most M203s and an M203 mounted on an M16A4 will fire considerably faster then when mounted on an M4A1.
 * Any kill with the undermounted Grenade Launcher counts to the guns kill total. Same goes for the Masterkey Shotgun and the Tactical Knife.
 * A kill with the M203 and GP-25 counts as a hipfire kill, however the Thumper does not count as a hipfire kill or a scoped kill due to its sight.
 * In Call of Duty 4 there were originally 3 more grenade launchers: AG36, HK79 and FN EGLM. The names can be found in localized strings.