C4

C4 is an explosive featured in Call of Duty 2, Call of Duty 4: Modern Warfare, Call of Duty 4: Modern Warfare (Nintendo DS), Call of Duty: Modern Warfare 2, and is also confirmed in the upcoming Call of Duty: Black Ops.

Single player
The C4 is constantly seen in the campaign as the primary weapon to take out key objectives, where the player would have to arm the explosive and travel to a safe distance before detonating the weapon. An example of this would be in the level "The Bog", where the objective is to destroy the ZPU-4 in order for a friendly helicopter to pass by. Also, the player will have to destroy an electronics tower with C4 in the level "Ultimatum".

Multiplayer
The C4 is a first tier perk and the player will get two when it is used, it has a higher damage than the claymore and also has higher splash damage than the claymore. When the perk is used, press left on the D-Pad and a detonation trigger will be pulled out, then by pressing the special grenade button (L2 on PS3, Left Trigger on Xbox 360) the C4 will be thrown, which will stick to walls, cars, etc. Pressing the equipment button (R2 on PS3, Right Trigger on Xbox 360) will then detonate the C4, albeit with a .83 second delay. Alternatively, C4 can be detonated by double tapping the reload button (use button in PC version) while the player's main weapon is out. Unfortunately the C4 is not popular in multiplayer modes due to the necessary remote detonation of the C4 which proves troublesome for Snipers and is commonly used by those who wait for someone to walk into the C4 then detonate it. The claymore is preferred more by Sniper players who rely on actually sniping, cutting off their view of the C-4. They often have no time to detonate the C4, whereas the claymore detonates automatically when an enemy walks in front of it. Most players use C4 in the Domination game mode and drop it at their flags. Since the game tells the player when they are losing a flag the C4 is then detonated. The disadvantage of this is that if the player dies, the C4 must be replanted. Another disadvantage of planting C4 at a friendly flag in Domination is that the C4 can be seen beforehand by the enemy and detonated by gunfire. This can be avoided if the player camps in a hidden location to watch the flag, to know when to detonate the C4.

Tactics
The remote action of the C4 requires an ambush tactic when used as a mine. Specifically, the user must know by sight, sound, friendly intel, or objective notification when the enemy is close to the C4. However, the advantage of using C4 over a claymore is user safety; the C4 can be thrown quite a distance to a spot that could be very open and hazardous.

C4 can be used as a grenade instead of a mine. For example, C4 can be used when the user is out of grenades, when the enemy is in a difficult spot, or when grenade cooking is needed, but not possible. This technique can also be used in conjunction with Martyrdom as if the user dies while holding the C4, the C4 drops and becomes live. The grenade will go off, triggering the C4, which has a slightly larger blast than a grenade.

C4 is used more often in objective-based modes like Search and Destroy, Sabotage, Headquarters, and Domination. When planting C4 at a point of interest, such as an objective, discretion is the key. Poorly-placed C4 acts only as a short deterrent. Superior placement for C4 involves dark corners, deep grass, or inside movable items (crates, boxes, trash, etc.). More importantly, the 3-Dimensional properties of the blast can be taken advantage of by placing the charge on the ceiling or on the underside of over-hanging ledges.

In Search and Destroy, do note that the targets that are being are being defended will be two crates on a single pallet, so they will have a separation in the middle. Throw C4 into this crevices, and detonate it remotely when the enemy is in the right position to be killed.

Some players enjoy 'suicide bombing' while using an SMG or the Sniper on the OpFor team, as it gives the player a shemagh (traditional head wrap which makes them 'look' like a suicide bomber as it hides everything but the eyes). They will equip Extreme Conditioning and Juggernaut so they can run up to the target, throw a C4 and detonate it quickly, usually killing them both. Although, not a very viable tactic, it is quite fun on Private Matches against other 'suicide bombers'.

In Search and Destroy and Sabotage, when planting or defusing the bomb, if they hold the L1 button while arming/disarming the bomb, the player will throw a fake C4 that cannot be blown up, but if enemies see it, they may attempt to destroy it, wasting their time and possibly giving away their position. Observant players will know that it is fake because the red light in the center will not be blinking. Players with Bomb Squad will know that it is fake because the skull icon will not appear over it.

It is worth noting that most players will not be actively looking out for C4s, especially in non objective-based matches, as many players are accustomed to using Claymores (or having them used against them). Therefore, a C4 is far more likely to go unnoticed if it happens to be in plain sight. Additionally, C4s are overall less conspicuous, as they do not emit trip lasers, like a Claymore, and they are not as bright.

In Domination, a good tactic is to throw C4 close to a flag, because the player will notice when an enemy is capturing it. It is best to try and hide it in scenery, or throw it into a dead body. This will make it less suspicious.

Call of Duty: Modern Warfare 2
C4 returns in Call of Duty: Modern Warfare 2, this time in the equipment slot instead of via perk. Another change is characters are given only one C4, but it is arguably more powerful and has a bigger blast radius than in Call of Duty 4: Modern Warfare, the throwing range of C4 is very low, requiring deliberate placement rather than throwing. Also, because it is in the equipment slot, it can be placed with a single button. This is noticeably faster than Call of Duty 4's method, which required switching to C4 as a weapon via the directional pad and then throwing it. But detonating is slower, since there's an animation of pulling out the detonator and activating it, in contrast with having the detonator already equipped in Call of Duty 4. Single player retains the method of assigning C4 to a directional pad button. However, C4 will detonate instantly if reload is pressed twice, essentially negating such disadvantages.

As with the previous game it is useful to place it on objectives (I.E. Domination flags, Sabotage targets, etc.) and use it as a mine whenever an enemy nears it. It can be used as a rudimentary grenade, but can't be thrown as far and must be detonated by the player. However, unlike fragmentation and Semtex grenades, there is no warning indicator for a nearby C4 satchel, and C4 can be detonated in midair by pressing reload twice quickly.

C4 also makes a return in the single-player levels of Modern Warfare 2, but rarely in the character's inventory - it is given when the player needs it for an objective (Plant C4 on bodies, etc.)

C4 will detonate if the player presses reload twice very quickly, (Except on the PC Versions, where the player must tap the "Use" key twice: "F" by default), which can be useful if the player has C4 previously set that needs to be detonated, but already has C4 in inventory from Scavenger or One Man Army. In this case, pressing the equipment button will not detonate the C4, it will simply cause the player to throw another C4.

There is a glitch that causes a detonated C4 pack to do no damage to an opponent whatsoever (no hit marker appears) no matter how close the enemy is to the C4 pack, or whether Danger Close is equipped or not. This glitch is currently active, though it may just be due to lag. This may be connected to another glitch that causes the C4 to show the explode animation but cause no damage. If any players walk into the explosion spot after a time of around 5 seconds, they will die (tested on PC in a private match via shared LAN connection).

Tactics

 * This is very good equipment for defense on Search and Destroy, Demolition, and Domination, especially for Snipers with excellent aim. One can quickly run up to the objective, plant a C4, and get to cover. When opposing players attempt to attack the objective, the C4 can be detonated, killing or severely wounding the opposing players.
 * C4 can be placed in doorways often used by the enemy. When one or more enemies are walking through it, using it can be an easy way to rack up kills.
 * Danger Close works especially well as it increases the blast radius.
 * C4 is especially effective if placed on the roof when indoors (e.g. the bunker in Afghan) as players never seem to look up. It also allows the blast radius to incorporate an entire room (if done properly).
 * If Scavenger is equipped and another is picked up, it can simply be shot, especially when using a Sniper Rifle or FAL with good range and zoom. This effectively turns it into a less reliable C4 detonated on the players command.
 * When defusing a bomb if C4 has been planted, pressing the trigger will result in blowing up the C4 but the player will still defuse the bomb.
 * In Domination, when an enemy is capturing a command point, the point will start blinking or the team announcer may alert players. Planting C4 at a command point and detonating it when this alert is given is an easy method by which to accumulate kills.
 * In Domination on Skidrow, there is some C4 on the wall at B. This is usually very good at hiding the players C4 as players are used to seeing C4 there. Another good place to plant it is by the A flag. Plant it in the window beside it. The C4 will go through the bars. Most players overlook that area. Wait or "camp" in the building beside A. Look out the little hole. When targets are in range, detonate the C4.
 * Plant it on a car, and wait there with a Heartbeat Sensor. When someone comes by the car, detonate it, getting a kill for a Humiliation challenge.
 * In Search and Destroy and Demolition use a Riot Shield, Danger Close, Scavenger and put the C4 on the bomb. Wait in a corner with the Riot Shield out for protection and detonate the C4 when a player gets close enough to it.
 * Another very popular tactic is to use C4 in Headquarters, deploy it in the area, stand outside the Headquarters and camp. Then, once there are enemies suspected inside, detonate the C4.
 * The player has a better chance of killing enemies with C4 if they put it in front of a claymore since the explosion from the claymore will detonate the C4. If a player has Lightweight it will be less likely for them to get by claymores when using this method.
 * Another Place to put a C4 is on the ceiling of buildings, as players rarely look at the ceiling when they enter a building.
 * A good tactic to use at Wasteland is to throw a C4 at the bunker entrance near the A bomb site's normal area, run around the bush to the entrance near site B and detonate the C4. This will draw attention to the other entrance ,allowing the player to enter through the other entrance and kill opponents.
 * In Search and Destroy or Demolition, using One Man Army by deploying 1 Claymore and deploying 1 C4 to enhance the explosion. It is good for protecting the bomb sites.
 * Last Stand Pro will give the player a last chance to detonate their C4 before dying.

Call of Duty: Black Ops
C4 will return in Call of Duty: Black Ops. It has been confirmed to be used in the level "Victor Charlie", where the player is tasked with planting C4 and run to a safe spot. It has also been confirmed that C4 will be in multiplayer.

Trivia

 * The C4 makes an appearance in the extended level of "F.N.G.", where Newcastle teaches the player how to arm and detonate a C4 block. He says "Looks like my ex-wife was kind enough to donate her car to further your education Soap." Watch the video.
 * In Call of Duty 4: Modern Warfare, when the player sprints, a package of C4 explosive can be seen in his left hand, even after he hasn't got anymore C4 packs left.
 * In Call of Duty: World at War, the C4 is replaced with the similarly-working Satchel Charge which can destroy tanks in MP and the bunkers in the SP level "Blowtorch & Corkscrew."
 * In Call of Duty Modern Warfare 2, if C4 is stuck to a pane of glass then the glass is broken, the C4 will appear to be floating in midair.
 * In Call of Duty Modern Warfare 2, in 3rd person mode, when the equipment button is pressed the player's character will hold the C4 and throw it, even if there is no C4 left.
 * C4 does not stick to a Riot Shield. It will just bounce off and land on the ground. The C4's adhesive might not attach to the shield's rounded surface, though this was likely for balancing reasons.
 * In Modern Warfare 2 C4 is affected by Flash and Stun grenades, being unable to detonate until the effect wears off. If C4 is placed by a planted bomb, before dying, detonate the C4 while it's being affected by the grenades, there's a big chance that it will blow up while the enemy is defusing the bomb due to the effect wearing off
 * A fake packet of C4 can be found on the RC-XD that is included in the Call of Duty: Black Ops Prestige Edition.
 * C4 was going to be a Modern Warfare 2 killstreak, but stopped that right before the game released.

Video
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Video showing an effective tactic when C4 is used with a Riot Shield