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. mission. However, on the Wii it is triggered by shaking the controller or by pressing down on the d-pad.
The knife will always kill enemy players in a single stab/slash, regardless of whether they are using the Juggernaut perk (Call of Duty 4) 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 will significantly increase its effective range by introducing a rather long-range lunge. Using the knife is considered a stealthy attack, 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.
In Call of Duty 4: Modern Warfare multiplayer, the knife has a number of challenges that will reward a player XP for using the knife in certain ways. These challenges include Knife Veteran, Slasher and Backstab.
When using the knife, the player will either lunge at the target if the target is far away enough, or if the target is close a slash will be used instead. 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 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 gun is unlocked early and has decent range and damage to compensate for the Tactical Knife's shortfalls. Also, if the health is set to double, you will have to stab twice.
The wide slash of the standard combat knife is not present when using 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 most commonly, sheer amusement. 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, will take out the care package marker but will not throw it, because their mobility (foot speed) is improved and hence are able to reach melee distance quicker, however this has been patched.
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 possibly while using Lightweight and a light weapon such as a SMG.
- In singleplayer, enemies don't use the knife unless scripted to do so. Instead, they will bash the player with the stock or barrel of the weapon they are currently holding.
- In Shi No Numa if you need reviving and you're in the water somewhere (this works in the comm room), you can use your knife and your player will jump out of the water.
- The knife models in the Call of Duty series are based on real-world knives, with minor cosmetic differences. The knife used in Call of Duty 4: Modern Warfare appears to be a SOG Bowie Knife, with the addition of a serrated back edge. The knife used in Call of Duty: World at War is the Kabar USMC Fighting Knife, almost identically. The knife used in Call of Duty: Modern Warfare 2 is a Blackhawk Tatang, with a slightly different grip.
- If grenades or the knife or both are used exclusively in any of the Campaign levels of Call of Duty: World at War on Normal difficulty or higher, an achievement or trophy can be earned called "Kamikaze". It is worth 15 GS on the Xbox 360 or a Silver Trophy on the PS3. The bayonet can be used in place of the knife, though, so it is frequently used for its longer reach.
- You can only stab on the Wii version if aim assist is activated.
- In Call of Duty: Modern Warfare 2, the weapon attachment Tactical Knife will allow the knife to be held when using the pistol, to allow a faster slash. This technique, usually used with a large-bodied flash light, is called the "Harries " technique named after proponent Michael Harries. Since the advent of smaller flash lights, this technique is considered outdated for use with them, because of the lack of recoil control with the second hand. It still sometimes taught for use with knives.
- In Call of Duty: Modern Warfare 2, it has been shown that a new knife called the Throwing Knife can be thrown at enemy players. It is treated as a piece of equipment, having its own crosshair and taking up a primary grenade slot. The knife can be retrieved after being thrown, for an unlimited amount of uses. The throwing knife appears to be smaller than the standard melee knife.
- In the Call of Duty Series it is possible to speed up reloading by using the knife, double-tapping the "switch weapons" button, or sprinting slightly while reloading once your magazine fills as opposed to waiting for the reload animation to finish. This technique is known as the Reload Cancel. Using a knife for this glitch is generally inadvisable as the recovery time of a slash will often be longer than waiting out the reload. Double-tapping the "switch weapons" button is most effective for this glitch, with a short sprint coming in at a close second..
- In Call of Duty 4: Modern Warfare, the G3 with a Silencer has an erroneously long Melee Charge Delay. The knife damage will only register 1.3 seconds after the players hits the knife button. This is a glitch caused by a typo in the game code.
- If you knife someone at point blank range you will slash them, however, if you are any farther than that you will perform a stabbing animation.
- In the Nintendo DS versions of the games there is no slash animation - only a stab animation.
- In Call of Duty: Modern Warfare 2, NPC's 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.
- In Call of Duty: Modern Warfare 2, in the level "Endgame", after the helicopter crash, your knife is the "Cold Steel GI Tanto" model when getting to Shepherd, but once he knocks you out, he stabs you with his own knife, which explain why your throwing knife is different at the end of the game from the melee knife you were just using.
- The Bayonet attachment in Call of Duty: World at War increases the range of your knife the same distance that Commando in Call of Duty: Modern Warfare 2 does. However, the bayonet slows down the speed of your melee attack.
- Using the knife in World at War produces a distinct and strangely loud sound, meaning a failed knife swing will almost always attract the attention of your intended target.
- When holding a Care Package type smoke grenade, a knife makes a crunch sound when used against an enemy.