Developement
Call of Duty 4 was developed by a team of a hundred people, over the course of two years. After Call of Duty 2, the Infinity Ward team decided to move away from the World War II environment of previous games in the series. This resulted in two game concepts: Call of Duty 4: Modern Warfare and Call of Duty: Modern Warfare 2. While developing the story for Call of Duty 4, Infinity Ward chose to avoid referencing current, real-life wars, and keep the series' common theme of two opposing forces of similar strength. To enhance the realistic feel of the game, the development team attended a live-fire exercise at Marine Corps Air Ground Combat Center Twentynine Palms, a training facility in the California desert. This helped the developers to simulate the effects of being near an Abrams tank when it fires. The team also talked with United States Marines who were recently in combat to get a feel for the background, emotions, and attitude of Marines in combat. Veterans were also recruited to supervise motion capture sessions and the artificial intelligence design of the game.
The development team designed the online multiplayer component to be balanced and rewarding for new players while still offering something for experienced players. An early idea to implement air support (air strikes and attack helicopters) involved players fighting over special zones to access a trigger for air support against enemies. This idea was discarded because it discouraged the type of deathmatch gameplay they intended. The kill streak reward system was put in its place to encourage the improvement of player skills. Players were allowed to select weapons before matches to get accustomed to weapons more easily and minimize weapon hunting. Maps were designed primarily for deathmatch games—the developers felt such designs suited other types of gameplay as well. Map layouts were designed to minimize locations players could hide from enemy gunfire.