On level 2, when the heli support comes in for an ammunition refill and repairs, go to the drop site and protect the helicopter at all cost. If it gets shot down, no more helicopters will arrive. Always keep moving and never stop or the mammoth class will send a barrage of homing missiles at you. The only way to avoid the missiles is to keep moving so that they cannot get a lock on you.
GunGriffon: Allied Strike