The Titan AT allows you to guide by aiming rather than locking on which is preferential for AT purposes as it does not give an incoming rocket warning.
Unguided rockets are fired directly in front of the vehicle. As a pilot, you have to adjust vehicle position or angle to change the aim of unguided rockets.
Guided missiles are only useful when target is locked. As a gunner, point at the target and press “T” to lock the target. Normal targets have a square sign, the locked target has an additional diamon mark. To switch to the next target, press “R”
Guided Missiles are best fired from a distance. Flying over the target is not necessary.