The first three games are played on a hexagonal grid for a map. Players not only control the combat units (ranging from infantry and tanks to helicopters, fighters and bombers, armored trains, surface warships and submarines, stationary gun turrets), but (especially in the later games) also many support logistics units (ammo and fuel transports, scout and radar units, road and construction vehicles, and others). Units have various weapons and can gain experience (which in later games can be transferred over in a campaign). Fuel and ammo is limited, and logistics require careful attention. Players also control buildings, where units can be repaired, and sometimes, produced. Weather conditions change, affecting unit movements (for example, a sea or river can freeze, immobilizing ships but allowing light units to move through it). Fog of war is prevalent and players have to use scouting units to gain information about the battlefield. Some of those options were added in expansions or sequels.