ADP 3-90, page 72

Chapter 4 4-12 ADP 3-90 31 July 2019 4-67. Commanders at all echelons track defensive preparations, such as establishing Class IV and V supply points and start or completion times of obstacle belts and groups. Commanders plan how units will restore obstacles that an enemy force has breached. Commanders use artillery, air, or ground systems to reseed minefields. Given time and resources, a defending force constructs additional obstacles in depth, paying special attention to its assailable flanks and rear. (See ATP 3-90.8 for additional information about obstacles and obstacle integration.) Enemy Airborne and Air Assault Attacks 4-68. Defeating an enemy airborne or air assault attack begins with a good IPB process to determine the enemy force’s capabilities to conduct vertical envelopment and to identify enemy airfields, pickup zones, drop zones, and landing zones. Armed with an appreciation of an enemy force’s capability to conduct vertical envelopment, commanders take steps to counterattack enemy forces before they launch, during their movement to the drop zone, or at the landing zone. Commanders may request joint offensive and defensive counterair support. After prioritizing the risk of each potential drop or landing zone to the operation, commanders establish surveillance of these areas to alert defending forces if an enemy insertion takes place. Units also sight their weapons to cover the most probable drop and landing zones. The fire support plan includes these zones in its target list for area fires munitions and scatterable munitions. Defending forces emplace obstacles in these locations and impede avenues of approach to critical friendly installations and activities as part of their countermobility and survivability efforts. 4-69. If enemy forces succeed in landing, a defending force contains and counterattacks them before they become organized and are reinforced. Friendly field artillery and attack helicopters must quickly engage enemy forces to take advantage of the concentration of targets in landing and drop zones. Joint fires can also be employed against such insertion areas. Available base and base cluster defense and response forces keep the enemy force under observation, designating targets for available fires. If more enemy troops land and consolidate, base cluster defense forces and the quick response force try to fix that enemy force to allow a tactical combat force to counterattack. Defending commanders may need to commit their reserve if an enemy force is too large for their tactical combat force to reduce. Limited Visibility and Obscuration 4-70. An attacking enemy force can be expected to create or take advantage of limited visibility conditions. Normally, a defending commander can expect an attacker taking advantage of these conditions to—  Conduct reconnaissance to locate a defender’s weapons, obstacles, and positions.  Breach or reduce defensive obstacles.  Infiltrate through gaps in a defender’s coverage caused by reduced target acquisition ranges. 4-71. Two limited visibility conditions exist: those which mechanical aids, such as thermal sights, can overcome or partially overcome and those which mechanical aids cannot overcome. The first category includes darkness. The second category includes dense battlefield dust, obscurants, heavy rain, snow, fog, or any other conditions which cannot be at least partially overcome by artificial illumination, image intensification, radar, or other sensors. In this case, defending units may need to move closer to the avenues of approach they are guarding. Sensors may still be of some value in these conditions. 4-72. Commanders use obscurants to disrupt an enemy force’s assault or movement formations and to deny an enemy force’s use of target acquisition optics, visual navigation aids, air avenues of approach, landing zones, and drop zones. Obscurants create gaps in enemy formations by separating or isolating attacking units and disrupting their planned movement. Obscurants affect both friendly and enemy forces. INTELLIGENCE 4-73. Just as in the offense, intelligence collection is continuous. Intelligence officers, in coordination with the rest of the staff, develop a synchronized and integrated information collection plan that satisfies the unit commander’s maneuver, targeting, and information requirements. These requirements in the defense are similar to those in the offense. Intelligence analysis helps commanders decide on the precise time and place to counterattack.