Knife

The knife is the standard close quarters combat melee weapon in Call of Duty 4: Modern Warfare and one of the melee weapons in Call of Duty: World at War, and Call of Duty: Modern Warfare 2.

Prior to Call of Duty 4: Modern Warfare, the knife was not a commonly used melee weapon in previous singleplayer Call of Duty games; it was available only in missions that feature stealth and/or reconnaissance. Before Call of Duty 4: Modern Warfare, the most common melee attack was the butt of the weapon. The knife is triggered by pressing the melee button (default V on the PC, clicking the right thumbstick on the Xbox 360, or clicking the R3 Button on the PS3), as taught in the "F.N.G." and "S.S.D.D." missions. However, on the Wii it is triggered by shaking the controller or by pressing down on the d-pad.

Multiplayer
The knife will always kill enemy players in a single stab/slash (unless you play old school free for all), regardless of whether they are using the Juggernaut perk (Call of Duty 4 and World at War) or the Painkiller Deathstreak (Modern Warfare 2). In Old School multiplayer matches, however, two knife attacks are required to kill an enemy player at full health. The knife is only effective at point-blank range, although the Commando perk (Call of Duty: Modern Warfare 2) will significantly increase its effective range by introducing a rather long-range lunge. Using the knife is considered a stealthy weapon and will not reveal the player's position on the minimap, allowing the player to perform stealthy kills without need of a suppressor. While inherently quiet, the knife will however make a rather thick slash or stab sound that is audible in close range.

When using the knife, the player will lunge at the target if the target is far away enough, or is in a certain position to the player, regardless of whether Commando is the active third perk or not. If the target is close range a slash will be used instead. Therefore, this is very important to take into consideration when choosing to knife the enemy. You can actually lunge at the enemy "Commando" style without having commando equipped, but this is an art that requires a good amount of practice to perfect. You may notice that you lunge at enemies sometimes even without commando. Also noteworthy is that while holding akimbo weapons in Call of Duty: Modern Warfare 2 the player will use a rather vicious quick stab attack. The slash attack has a wider range and hence a higher chance of landing at point-blank range; although the lunge naturally has a longer-range due to the thrusting movement of the player. Experienced players will use the knife when out of ammo and indoors, but will switch out an empty weapon for a new one at the first chance. The usefulness of the knife in Hardcore modes is somewhat lessened due to most weapons being able to kill in one to two hits at close range. It is however still useful as a silent, close-range and ammo-less attack.

The Tactical Knife is a weapon attachment in Call of Duty: Modern Warfare 2 that approximately halves the cooldown time of the melee attack; effectively allowing the player to perform stabs at twice the speed. Handguns are the only weapons compatible with the tactical knife, which is unlocked after obtaining 75 kills with the USP .45 or M9 or 100 kills with the Desert Eagle or .44 Magnum. The .44 Magnum is one of the more commonly used Handguns for this purpose as the tactical knife is already attached to it in a default class (First Recon), meaning players only need to use this class and the tactical knife attached to the .44 Magnum to then unlock it for custom classes (after Level 26). Also, if the health is set to double, you will have to stab twice.

The wide slash of the standard knife is not present when using a handgun equipped with a tactical knife but the window in which the opponent may be lunged seems widened. The lunge is also far faster with the tactical knife. Players often have classes dedicated to knifing, either for tactical diversity, sowing chaos, or sheer amusement and is often looked down upon by other players. These players often equip a maximum-mobility primary weapon (Sniper Rifle or SMG), Marathon (Perk 1) and Lightweight (Perk 2) to maximize their running speed and time spent running. The range bonus provided by Commando sees it used as the Perk 3 in the majority knifing classes, while the stealth granted by Ninja is also a viable option.

Some players, upon earning a care package, used to take out the marker but not throw it. This would increase their movement speed allowing them to lunge at players well before they could react. The care package marker's mobility stat has been patched, making this tactic useless.

When in third person mode, use of the knife attack in prone gives the appearance of swinging the equipped weapon at the enemy. Upon closer inspection the knife appears to stick out of the weapon, like a badly mounted bayonet. This glitch was also present in COD4, although it has no effect on gameplay.

It is possible to dodge a knife lunge, leaving the knifer defenseless for a short while, though this is only generally possible while using Lightweight and a light weapon such as a SMG.

The knife cooldown time can be shortened by quickly hitting the equipment button then switch weapons button.

Trivia

 * In Modern Warfare 2, the knife model is a Blackhawk Tatang, a large combat knife with an 8" blade used by multiple military branches.
 * In World at War, the knife is a KA-BAR made famous by the USMC. The fact that the knife also appears in the Soviet campaign is strange as the Russians never fielded the weapon.
 * In Call of Duty: Modern Warfare 2, NPCs now have the ability to use the knife, although it is extremely rare. Allied NPCs will usually throw enemy NPCs onto the floor and shoot them upon close contact instead of using the knife.
 * When holding a Care Package type smoke grenade, a knife makes a crunching sound when used against an enemy.
 * The only time an enemy uses a knife against the player in Call of Duty 3 is during one of the quick-time events, when you are ambushed in a building by a German soldier wielding one. The German repeatedly attempts to stab the player. The fight ends when you manage to push his knife into his own chest, where he comically stares at it before falling dead.
 * In Modern Warfare 2, when Soap goes to kill General Shepherd in "Endgame", he holds the knife in his left hand and nothing in his right while the player is able to attack by hitting the fire button, this is the only time in the whole of the Call of Duty series that the player holds a knife as a primary weapon. Call of Duty: Black Ops is an exception as little is yet known.

Video
thumb|left|300px|Gameplay with the Tactical Knife in Modern Warfare 2