ATMs are anti-tank missiles with a HEAT warhead. They have excellent penetration, lock on capability, and can be fired from cover. Certain vehicles can have to 2 or up to 5 rockets, while others can fire unlimited amounts.
ATMs are best used against vehicles with heavy armor, or to disable enemy vehicles without trading damage. They have limited range and cannot be used for close combat. Active-Protection System decreases the chance of penetration. Smoke Gernades hide your Vehicle and doesn't allow enemy ATMs to lock on, they also can block ATMs once they were fired. Spaced armor affects the ATM the same way it affects a HEAT warhead.
Players on the forum have been debating whether to have it be unlimited or not. There have also been suggestions to raise the amount of atms each player can get at a time.