There are several dimensions to this subject. The first is the notion that fire may be against an opportunity target or may be prearranged. It the latter it may be either on-call or scheduled. Prearranged targets may be part of a fire plan. Fire may be either observed or unobserved, if the former it may be adjusted, if the latter then it has to be predicted. Observation of adjusted fire may be directly by a forward observer or indirectly via some other target acquisition system.
Counterbattery fire: delivered for the purpose of destroying or neutralizing the enemy's fire support system.
Counterpreparation fire: intensive prearranged fire delivered when the imminence of the enemy attack is discovered.
Covering fire: used to protect troops when they are within range of enemy small arms.
Defensive fire: delivered by supporting units to assist and protect a unit engaged in a defensive action.
Final Protective Fire: an immediately available prearranged barrier of fire designed to impede enemy movement across defensive lines or areas.
Harassing fire: a random number of shells are fired at random intervals, without any pattern to it that the enemy can predict. This process is designed to hinder enemy forces' movement, and, by the constantly imposed stress, threat of losses and inability of enemy forces to relax or sleep, lowers their morale.
Interdiction fire: placed on an area or point to prevent the enemy from using the area or point.
Preparation fire: delivered before an attack to weaken the enemy position.
Deep supporting fire: directed at objectives not in the immediate vicinity of own force, for neutralizing or destroying enemy reserves and weapons, and interfering with enemy command, supply, communications and observation; or
Close supporting fire: placed on enemy troops, weapons or positions which, because of their proximity present the most immediate and serious threat to the supported unit.
Neutralization fire: delivered to render a target temporarily ineffective or unusable; and
Suppression fire: that degrades the performance of a target below the level needed to fulfill its mission. Suppression is usually only effective for the duration of the fire.
The targeting process is the key aspect of tactical fire control. Depending on the circumstances and national procedures it may all be undertaken in one place or may be distributed. In armies practicing control from the front, most of the process may be undertaken by a forward observer or other target acquirer. This is particularly the case for a smaller target requiring only a few fire units. The extent to which the process is formal or informal and makes use of computer based systems, documented norms or experience and judgement also varies widely armies and other circumstances.