In multiplayer, an attack helicopter (the AH-1 SuperCobra for SAS/Marines and the Mi-24 for OpFor/Spetsnaz) can be summoned to provide fire support for the player's team with a 7-kill streak. Once summoned, the helicopter will follow a pattern circling around the map once, looping back to where it started, and then will leave. Helicopters will search for and kill any enemies with machine guns and (contrary to popular belief) very rarely, utilize rockets (it is possible, albeit extremely rare, to be team killed by a friendly helicopter in hardcore game modes).
Helicopter support will not stack; a player who has achieved a 7-kill streak will have to wait until the current helicopter leaves or is shot down to call in a new helicopter. Lower tier air support (i.e. UAV and airstrike) can be activated at same time a helicopter is active. The helicopter will leave after approximately 2 minutes at most, but can leave earlier. Helicopters are believed to attack players who are in first and in that order to the worst, although this has not been proven.
Helicopters have 1100 hit points. They will take 30% damage from bullets until they have lost 550 hit points, where they will take full damage from bullets. Helicopters will also use evasive maneuvers after losing 550 hit points, and will attack and move faster during evasive maneuvers. Shooting down a helicopter is an option, with the RPG and light machine guns being the most effective weapons. One hit from an RPG rocket will deal 1000 damage, 91% of a helicopter's hit points. A player with an RPG and the Sonic Boom perk (which increases the damage of the RPG by 25%) will deal 1250 damage to a helicopter with one hit from an RPG rocket, thus destroying it. Mounted M249 machine guns are also effective, often more so than RPGs, as it can easily take down a helicopter in around 5 seconds. Players should remember that although a helicopter will never open fire without line of sight, it will often continue firing at a player who has taken cover, and its bullets penetrate most surfaces.
While the AH-1 SuperCobra and the Mi-24 Hind helicopters are identical in performance, the Mi-24 is much larger than the AH-1, making it a much easier target for RPGs, while it is harder to hit the AH-1 unless it's very close to the RPG user.
A helicopter will assess certain factors when deciding which players to engage (factors not listed in any particular order):
- Distance between the enemy and the helicopter; helicopters will attack closer targets first
- Whether the player has attacked the helicopter before; helicopters prefer to attack the player who most recently attacked them
- The weapon an enemy player is using; a helicopter is more likely to attack an enemy player with a LMG-Sniper Rifle-Assault Rifle-SMG-Shotgun. Contrary to popular belief, carrying RPGs does not increase the chance of a helicopter shooting the player.
- Player stats for the current game, such as kill-to-death ratio; a helicopter will likely attack an enemy player with a high kill-to-death ratio.
- The helicopter usually will not finish off someone it puts into Last Stand. However, it will occasionally kill a Last Stand user fully.
The kill-to-death ratio and the number of points seem to be the most important factors in deciding who will be attacked.
In multiplayer, if shot down (either with an RPG or automatic weapon), the helicopter's tail will explode, causing the chopper to spin out of control, eventually exploding just outside the map, always in the same place, regardless of where it was destroyed.
- If the player dies and calls in a support chopper, the chopper's kills will count for the next killstreaks.
- Although extremely rare, it is possible to be killed by the helicopter's rocket when it fires.
- It is possible for a helicopter to kill the player that called it in. It is even possible for it to get a headshot on the player. It will appear as the headshot icon on the kill list and the player's name next to it.
- It is possible to plant a C4 charge on an attack helicopter in the map Overgrown when the helicopter hovers just above the field between the barn and the L-shaped building with the mounted gun.
- Rarely, when a player calls in the chopper in one life, but gets killed and calls in a UAV in the next life, the helicopter kills will keep on getting UAVs over and over instead of getting higher killstreaks. This glitch ends once the helicopter goes away.
- In a private match, changing the radar to "always on" makes the Airstrike and helicopter require three and five kills respectively. This also applies to Split-Screen matches.
- If the player uses free spectate and goes up to the helicopter they will see there is no pilot.
- The attack helicopter in Call of Duty 4: Modern Warfare seems to fly closer to the ground then any other attack helicopter in a Call of Duty game, possibly to counteract the lack of guided launchers.
- Call of Duty 4: Modern Warfare is the only game in the Call of Duty series where the attack helicopter actually uses its missiles in multiplayer.