The earlier games in the series are set primarily in World War II, including Call of Duty, Call of Duty 2, and Call of Duty 3. While Infinity Ward is still a developer, Treyarch and Sledgehammer Games also develop several of the titles with the release of the studios' games alternating with each other....
The player has two primary weapon slots, a handgun slot and can carry up to eight grenades (all of the later Call of Duty games feature only two weapon slots; a sidearm will fill one of these slots). Weapons may be exchanged with those found on the battlefield dropped by dead soldiers.