Flashbang

The M84 stun grenade is the flashbang used in Call of Duty 4: Modern Warfare and Call of Duty: Modern Warfare 2. A flashbang is a grenade that releases a flash of light that momentarily activates all photosensitive cells in the retina, making vision impossible for approximately five seconds until the eye restores the retina to its original, unstimulated state.

Subjects affected by flashbangs describe seeing a single frame for the five seconds (as if their vision was "paused") until it fades and normal sight returns. This is because the sensory cells which have been activated continue sending the same information to the brain until they are restored to their resting state, and the brain translates this continuous information into the same image. The incredibly loud blast emitted by the grenade contributes to its incapacitative properties by disturbing the fluid in the semicircular canals of the ear.

The flashbang has been around for almost five decades, for the reason being that the British Special Air Service needed a non-lethal incapacitant for special operations. Although there are many different types, the one used in Call of Duty 4: Modern Warfare is the USA standard issue M84 flash grenade that is made by Picatinny Arsenal of America.

The flashbang is an essential item for both Modern Warfare and Modern Warfare 2, especially when playing Veteran difficulty. AI-controlled enemies are responsive to flashbang detonations and it is required to consistently defeat certain foes, such as the Juggernauts

Tactics
The Flashbang grenade can be effectively used on a defended location or around a corner. Flashbangs will detonate seconds after being thrown. They cannot be cooked. If the target is close enough and looking at the detonation site, they will be temporarily blinded and deafened. The target’s reaction is still in real time so they can run or back-up to evade, however, they cannot sprint while affected. They can still easily fire, making any enemy in front of them a potential kill. Any affected target will raise their arm to cover their eyes, allowing the player to know that they are blinded.

In the single-player game, you spawn with and can find flash grenades in grenade bags, but they only show up in bags when you don't have a lot of them. In multiplayer, if you go into Last Stand while cooking a flashbang it will turn into a frag grenade. Flash Grenades can go off in the air. They will not wait until they hit the ground like Stun grenades, so don't chuck them straight up. In fact, the Flash Grenade goes off exactly one second after being thrown, so aim wisely.

Because it only affects players' vision if they are facing towards it, a viable tactic is to turn away before it detonates or to duck behind cover. This is most effective if you have to throw a flashbang in close proximity. Additionally, the flashbang can inflict a small amount of damage (15 points), which can kill a target at low health.

Versus Stun Grenades

 * In Call of Duty 4: Modern Warfare a flashbang does not indicate if it has affected the enemy, making it difficult to discern whether it has had any effect. Stun grenades on the other hand, show the damage indicator if they've affected anyone, thus making stun grenades more popular. However, in Call of Duty: Modern Warfare 2, this is not the case.
 * Flashbangs have a larger "range" than stun grenades, in that they can affect targets further away, but at the edge of the range players are only affected if they are looking in the direction of the flashbang. This is double edged sword as flashbangs are more likely to end up affecting the thrower as well.
 * Exploding stun grenades do more damage to affected targets than flashbangs do. It is more likely to kill a wounded player via a stun grenade explosion.
 * Stunned players move and aim more slowly. Flashbanged players are simply blinded and deaf but move and aim just as well (though they cannot sprint.)
 * Flashbangs will explode in midair. Stun grenades must impact something first.
 * Flashbangs take longer to arm than stun, about double the time, which could be the death of you if you need to throw it into a room quickly.
 * Players affected by a stun grenade can still see clearly and react to their surroundings, albeit very slowly. A flashbang, however, can completely disorient a player, as they have no extravisual perception.
 * Blast Shield protects users from stun grenades but Flash Grenades will still blind a Blast Shield user.
 * Because Stun Grenades slow the enemy, require hitting a surface and have a smaller blast radius and indicate if a target has been affected, they are used more often than flashbangs.
 * Flashbangs can disable placed C4 and claymores temporarily.

Trivia

 * The Spetsnaz forces shout something as "flash ba(ng)", this being incorrect. Flashbang in Russian is светозвуковая граната (svetozvukovaya granata).