During a game, players are given a pre-determined amount of reinforcement points, with which to purchase units with varying costs. Once the player deploys the units they purchase, they must wait 20 seconds for them to be airdropped to the field. If a unit is destroyed, the points are refunded to the player in order to allow them to bring in more units. During the single-player campaign, most missions vary what units the player can recruit, while some missions will offer the opportunity to recruit free units, though these cannot be replaced if destroyed. Each unit has strengths and weaknesses, such as mobile anti-air guns being most effective against enemy helicopters, and repair tanks being most effective at keeping vehicles and armor repaired. Each unit possesses a defensive ability, such as deploying smokescreens, while some units possess an offensive ability, such as marking targets for bombardment or using grenade launchers on enemy infantry. Once a unit's special ability(ies) has been spent, players must wait for them to recharge before they can be used again.