Army Men: World War - Land, Sea, Air features two modes for single player: Campaign and Boot Camp, as well as featuring a two-player "capture the flag" multiplayer mode. The player can choose from three difficulties: Easy, medium or hard.

The Campaign is the main mode for Army Men: World War - Land, Sea, Air. Set in a "realistic" setting like the previous Army Men, it features 15 missions in total, which involves the player (as a Green soldier) completing certain objectives that may involve intercepting vehicles, escorting friendly soldiers and killing enemies on land, sea or air. The plot begins with the Tan Army attacking the Green Army by air and the Green Army later taking revenge, with the narrator announcing: "We shall beat them on all fronts, returning force with force, whether it be by land, sea or air."

Boot Camp is a training level in which the player learns the controls. It consists of training areas for all weapons and an obstacle course.