The American campaign begins with Private Martin, a member of the 506th Parachute Infantry Regiment, training at Camp Toccoa in the U.S. state of Georgia, on August 10, 1942. This level is meant to familiarize the player with the game controls.

During the single-player campaign, the player controls six different characters from a first-person perspective. The player assumes the role of a recent recruit to the British Special Air Service (SAS), Sergeant John "Soap" MacTavish for most of the game, starting with his induction into the 22nd SAS Regiment.