brigade and its batteries to the brigade's battalions. However, some armies achieve this by placing the assigned artillery units under command of the directly supported formation. Nevertheless, the batteries' fire can be concentrated onto a single target, as can the fire of units in range and with the other tactical missions. Application of fire There are several dimensions to this subject. The first is the notion that fire may be against an opportunity target or may be prearranged. If it is 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. NATO also recognises several different types of fire support for tactical purposes: 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. These purposes have existed for most of the 20th century, although their definitions have evolved and will continue to do so, lack of suppression in counterbattery is an omission. Broadly they can be defined as either: 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