Composition 4 is an explosive featured in Medal of Honor (2010) and Medal of Honor: Warfighter. It is essentially the replacement for Composition B explosive, which was featured in past Medal of Honor games.
Medal of Honor (2010)
C4 is used during the mission Dorothy's a Bitch, and is used to destroy an anti-air emplacement.
C4 is an explosive available to the Coalition team. It is available to the Coalition faction's sniper class, who obtains two C4 charges. It is capable of damaging vehicles and killing enemies. In addition, C4 is the device set when a player arms an objective with a bomb. The Opposing Forces' IED is considered as that team's version of the C4.
Medal of Honor: Warfighter
A Remote Charge is a confirmed weapon to be featured for the Demolition class for the multiplayer portion of the game. It is technically SEMTEX (evident by the word "SEMTEX" written on the explosive when the player deploys it).