FGM-148 Javelin

The Lockheed Martin FGM-148 Javelin is an American man-portable anti-tank guided missile.

History
The FGM-148 Javelin is a state-of-the-art anti-armor system produced for the U.S. military. The Javelin uses either a 'top-attack' method to penetrate the thinly armored turret or roof of MBTs and other armored vehicles, or a 'direct fire mode'. Once fired, the missile "pops out" of the launch tube and ignites in mid-air. The missile then rockets skyward to an appropriate angle from which to hit its target at about a 90 degree angle. Apart from the U.S. armed forces, the Javelin is also operated by nations such as the U.K., Australia, Ireland, New Zealand, Jordan, the Czech Republic, Taiwan, and the UAE. It is currently being used in Iraq and Afghanistan.

Call of Duty 4: Modern Warfare
The FGM-148 Javelin appears exclusively in the single-player campaign, most notably in the missions, "The Bog" and "Heat". It can also be found in "Safehouse", "All Ghillied Up", and "All In". It can't be fired in enclosed spaces, or a message telling you that there isn't enough room will appear. Also, when it is fired so that the missile ignites near a friendly A.I, the the player will fail the mission and a message will show up on the screen saying, "Friendly fire will not be tolerated!" This is probably due to the fact that the missile igniting burns the teammate, but the teammate in question does not actually die. Occasionally, such as in "Heat," the Javelin missile can get 'hung up' on a roof if fired too close, due to the missile not having the chance to ignite.

Call of Duty Modern Warfare 2
The FGM-148 Javelin returns in Modern Warfare 2. In campaign, the Javelin first appears in the level "Of Their Own Accord", where the player is tasked with sniping Russian soldiers armed with Javelin launchers. The player then gets an opportunity to pick up a Javelin and destroy Russian armor and attacking Mi-28 gunships with it. The Javelin later appears in "Loose Ends", where Archer uses one to destroy Ultranationalist vehicles.

In Multiplayer, the Javelin is the penultimate launcher to be unlocked, being unlocked at level 50. It functions similarly to the Stinger, but has a more sophisticated targeting system: vehicles can be targeted behind cover with arrows pointing to their location. A short beeping noise will confirm when the player has a solid lock on the vehicle. This effectively allows the player to fire in cover, providing there is enough room to fire the rocket. It can shoot down most attack helicopters in a single hit and the Pave Low in two, or sometimes even in only 1 if it tricks the Pave Low or if it has already deployed its flares. It has been confirmed that the Javelin can even destroy enemy UAVs. The Javelin can destroy enemy Harriers, although due to the size of the Harriers fuselage, the Javelin missile will miss and then turn and try to destroy the harrier in mid-air. However, it has a second function which the Stinger does not have: the Javelin is able to lock onto areas on the ground, effectively making it a sophisticated, shoulder-mounted mortar.

When firing the Javelin, the user must be careful to have enough vertical clearance as the rocket will fly forward a short distance then straight upwards. If there is a roof or overhang above and in front of the user, the Javelin will detonate, killing the user and those around them.

The Javelin has unusual loading behavior. A user can actually carry 2 missiles, one in reserve and one in the launcher. After spawning, the player's missile is actually in the reserve slot. Upon drawing the weapon for the first time, the missile is loaded into the launcher, opening the reserve slot. Additional missiles can only be acquired if the reserve slot is open. Because of this using Scavenger and Javelin can be a little confusing. The player must draw the launcher and let the reload complete at least once to get a second missile. After firing, the Javelin will switch back to the primary weapon without reloading. This means that after firing the launcher, a reserve missile, if present, will NOT be loaded into the launcher by default which means the reserve slot will remain full, which means running over an ammo bag will NOT increase the user's missile count to two. The user must switch back to the Javelin, wait for the long load animation to complete, then run over the ammo bag to pickup the second missile. Contrary to popular belief, the Scavenger perk does in fact give Javelin ammo, even if it is not the primary weapon.
 * As of the latest patch on the PS3 and Xbox 360, the Javelin now starts the game loaded with one rocket, with no rockets in reserve.

Modern Warfare: Mobilized
The Javelin makes an appearance in Call of Duty: Modern Warfare: Mobilized as one of the three launchers in game, the other two being the RPG-7 and the Explosive Tip Crossbow. It is the same as the console versions, but possible targets are shown in black boxes instead of green, and there is no restriction to where it can be fired.

Trivia

 * In order to fire off successive shots, a spent launch tube has to be detached from the CLU and a new one attached in place. This of course would be cumbersome to depict during game play, as a result, the Javelin is simply lowered off to the side while reloading.
 * In Call of Duty 4, the Javelin will automatically reload with no animation of the operator handling the missile.
 * Much like a real Javelin system, the Javelin takes a top-attack flight profile when attacking armored vehicles, with the strange exception of "All In" where the missile will fly directly towards the enemy BMPs, just like how the Stinger flies directly towards aircraft (straight on). Even the direct-fire mode of the Javelin will still go up in the air.
 * It is possible to fire the Javelin and make it hit a building rapidly in "All In". The player needs to shoot the second BMP near the silos, take the Javelin to the beginning and fire. It will hit a building, killing troops and possibly the BMP itself.
 * In real life, the cost of each Javelin is $125,000 and cost of each missile is $80,000.
 * On the map Estate the Javelin can be fired from a distance into the house through the roof.
 * In Modern Warfare 2 the Javelin appears to have an expiration date which can be read below the sight saying 'EXP. DATE:05/19/79'. This could mean 2079.
 * If one shoots a Javelin at air support and it is destroyed when the missile shoots up, the rocket will continue upwards before coming down, occasionally leading to suicides from standing under air support.
 * You can actually hold your breath while using the Javelin, just like sniper rifles.
 * It is often compared to the Stinger, as the Javelin works behind cover, and can hit players, but the Stinger will chase a vehicle, a Javelin will not. It is up to personal preference.
 * It is very strange that the Russians in the American Defense Campaign now have access to the Javelin. They likely found a Javelin cache somehow and stole it.
 * In the mission "Of Their Own Accord", a group of Russian solders is shown firing javelins at US armor. This is inaccurate though, as the USA has placed safety measures in the missiles programming to prevent them from ever being able to be used against US Forces. In reality, the missiles would fire, fly over their target, and then simply continue flying away, never actually engaging the target. Although the Russians would be using 9K115-2 Metis-M in real life, Infinity Ward most likely did not want to make another weapon in to the game as that could delay the game's release.
 * It is also strange that the Javelins you pick up immediately locate and highlight enemy vehicles, without visible adjustment from their previous behavior.
 * During multiplayer, in absence of vehicular targets the Javelin will automatically lock on to whatever spot that the user aims at. Once fired, the missile will fly upwards and hit the target area several seconds afterwards, unleashing a fairly large and lethal explosion, similar to, yet smaller than that of the Predator killstreak. Because of the nature of the weapon, it will always hit the target from above, so make sure your target has line of sight to the sky (in fact, this can even allow you to hit locations that would normally be sheltered against launchers, such as walled-in rooftops, buildings with derelict roofs, or even skylights on Terminal). However, using Danger Close can increase the radius and lethality of the explosion. It is worth noting that the delay between firing and impact is considerable, even a hindrance to reliably getting kills, so it is recommended to use it more as an anti-camp solution or against high traffic objectives like bomb sites or domination nodes.
 * Despite being primarily an anti-armor weapon, the Javelin does have the ability to fire on aircraft in real life. According to the army field manual, the Javelin is capable of locking onto and firing at low-flying aircraft (mainly helicopters) when used in the direct-fire mode.
 * During the level "Of Their Own Accord" (at least on PC), locking on to helicopters does activate direct-fire mode, with the on-weapon display showing a "DIR" icon rather than "TOP". The missile will still launch skyward, but will quickly adjust mid-flight to hit the helicopter. The delay between firing and impact is significantly shorter than in top-attack operation. Whether this same behavior occurs during multiplayer or on consoles has yet to be verified.
 * When you fire at enemy Harriers, sometimes the missile will miss and return to the Harriers and miss again, then fly strangely toward to you.

Glitch
As of the December 11th Patch, this Glitch has been fixed for all Consoles.

Upon release of Modern Warfare 2 there was a very popular glitch which was typically called the Javelin Glitch. Many players had abused the glitch. It has successfully been removed from the PC, Xbox 360 and PlayStation 3 version. This glitch worked with all Launchers except the Thumper, likely due to its required detonation range.

The glitch involved having any equipment aside from a Frag Grenade, and any launcher (except the Thumper) equipped; the user had to have the Launcher as their current weapon; they would then hold the equipment button, switch back to their Launcher, and run around the map waiting to be killed, when the glitch would execute.

When the glitch was used, upon the user's death, a live missile would immediately fall out of the launcher and detonate on the ground. Given the very large blast radius of launchers it was generally an instant kill. To counter the glitch, players would attempt to kill the glitchers at a distance from themselves and/or their teammates. As an alternative, players would try running away, or, as a last resort cooking a frag grenade/sticking a semtex/shooting your feet with an RPG-7 when the glitcher got close. This would still result in a suicide but the shooter would receive a kill, where as the glitcher would not; however a keen sense of timing was necessary to pull it off successfully. The "Javelin Glitch" was typically executed in such a way that - regardless of death or injury - the user would receive a kill, by means of standing within proximity of enemy players so the explosion connected. The perks Marathon, Lightweight (or Danger Close), and Commando were often used to exploit it further, which allowed for users to sprint infinitely and move around at a fast pace, melee knifing the unaware, and "exploding" in front of those who happened to spot them. It was also possible to kill a glitcher during the knife swing animation to avoid the glitch occurring as the launcher is not considered the active weapon during that time and will not fire.