ADP 3-90, page 67

The Defense 31 July 2019 ADP 3-90 4-7 units typically employ field fortifications and obstacles to reinforce the terrain’s natural defensive aspects. The MBA includes the area where a defending force counterattacks that defeats or destroys enemy forces. 4-34. In contiguous operations, the MBA extends from the FEBA to the rear boundary of a specific echelon’s subordinate units. Commanders locate subordinate unit boundaries along identifiable terrain features and extend them beyond the FLOT by establishing forward boundaries. Unit boundaries should not split avenues of approach or key terrain. Commanders select the MBA based on the products of the IPB process and their own analysis using the mission variables. The IPB anticipates how an enemy force will use the available avenues of approach. SECURITY AREA 4-35. A security area is that area occupied by a unit’s security elements and includes the areas of influence of those security elements. It may be located as necessary to the front, flanks, or rear of a protected unit, facility, or location. Forces in a security area furnish information on an enemy force; delay, deceive, and disrupt that enemy force; and conduct counterreconnaissance. All units perform security operations within their AOs, including the support area, to deny enemy reconnaissance and otherwise protect the force. Units implement security operations and other information protection measures to deny the enemy force information about friendly dispositions. 4-36. Commanders conduct security operations to provide their forces time and space to react to the approach of enemy forces by causing the enemy to deploy prematurely. This reveals the enemy forces’ main effort and which of the available avenues of approach the enemy is using. Commanders conduct security operations to conceal the location of their main battle positions, prevent enemy observation of friendly preparations and positions, and prevent enemy forces from delivering observed fire on these positions. Commanders can offset an attacker’s inherent advantage of initiative regarding the time, place, plan, direction, strength, and composition of the attack by forcing that enemy to attack into unexpected prepared defenses. They counter enemy ground and air reconnaissance activities through both active and passive measures. Commanders must not permit enemy reconnaissance and surveillance assets to determine the precise location and strength of defensive positions, obstacles, engagement areas, and reserves. COMMON DEFENSIVE PLANNING CONSIDERATIONS 4-37. The defense is more effective when commanders and staffs have adequate time to thoroughly plan and prepare defensive positions. Lack of preparation time may cause a commander to maintain a larger-than- normal reserve or accept greater risk. All units must be capable of mounting a defense with minimal preparation. A defending commander can increase the effectiveness of the security area, establish additional alternate and supplementary positions, refine the defensive plan including branches and sequels, conduct defensive rehearsals, and maintain vehicles and personnel. 4-38. To gain time to organize a defense, commanders may order the security force to conduct a delay while the main body disengages and moves to more advantageous positions. The security force must know how long it needs to delay enemy forces for the main body to prepare its defense, and it must be task-organized to conduct a delay. 4-39. When an attack begins, a defending commander yields the initiative to enemy forces. Defending forces maintain security and disrupt enemy attacks at every opportunity. Defending commanders disrupt enemy attacks by using long-range fires to reduce the impact of the attacking enemy forces’ initial blows and start wresting the initiative from enemy forces. Defending forces draw enemy forces into engagement areas where they can initiate combat on favorable terms. Commanders surprise enemy forces with concentrated and integrated fires against exposed enemy formations from concealed and protected positions. They then counterattack enemy forces, preferably when those enemy forces are most vulnerable to friendly capabilities. They exploit small tactical successes and opportunities to disrupt an attacker’s momentum. 4-40. Defending forces do not have to kill every enemy soldier or destroy every combat system to accomplish their mission. They only have to eliminate the enemy force’s ability to synchronize a combined arms team or break the enemy’s capacity to fight. Those events signal a transition that affords defending commanders the opportunity to seize the initiative and transition to the offense.