The Abrams tank is the most efficient tank in the game. It has several stages it will process through:
1) From the factory, the tank is produced with a 120mm gun and no secondary armament.
2) Upon achieving its second promotion, the tank will be upgraded with a better gun and two machine guns to attack infantry.
3) Upon achieving its fourth promotion, the tank will be upgraded with a better gun and two missiles to attack air targets.
4) Upon achieving its sixth promotion, the tank will be fitted with a 145mm gun, a laser-based CIWS against infantry and aircraft, and a firing post for two passengers.