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Chapter 4

Passive Air Defense Measures

This chapter focuses on types of passive air defense measures, to include self-defense measures in a convoy. Units may be exposed, bunched up, or in a situation where they are vulnerable to taking unnecessary casualties. If attacked under these conditions, the unit has the option of fighting back. The decision to engage hostile air must consider the unit's assigned mission and the tactical situation. In cases where the enemy aerial platforms are outside the range of the unit's weapons, a unit's most attractive option can be to seek cover. In other cases, commanders may decide to place the enemy aerial platform under fire with organic weapons with the intent to frighten them off.


  4-1. Passive air defense measures are all measures other than active defense taken to minimize the effects of the hostile air action. Passive defense measures are of two types: attack avoidance and damage-limiting measures. Both include the use of cover, concealment, and camouflage; protective cover; and deception.
  4-2. Accept as a foregone conclusion that the enemy has the capability to attack from the air and that they will exercise that capability. Air attack is not a probability- it is a certainty. Small units do not stand helpless before this threat. Simple, commonsense measures can be taken by a small unit to avoid attack and to limit damage if attacked. Passive air defense measures, if routinely followed, will reduce the probability of attack and will limit damage if an attack cannot be avoided.
  4-3. The first line of defense against air attack is to constantly apply passive air defense measures. If the aerial platform is not attacking the unit, the unit commander has a decision to make. First, the commander may not want to fire and disclose the position. Secondly, to engage a nonattacking aerial platform, it must be positively identified as hostile. This may be difficult unless unit personnel have had aircraft recognition training. Remember, if not under attack, the unit commander must give the order to fire at the aerial platform.

4-4. Attack avoidance means taking the actions necessary to avoid being seen by the enemy-concealment and, lacking concealment, camouflage. What can be seen can be hit, and if you cannot be seen, the probability of being hit diminishes to near zero. The techniques, procedures, and materials used for concealment from aerial observation are the same as used for concealment from ground observation (see Figure 4-1).

4-1. Attack Avoidance.



4-5. There are three concealment principles employed (siting, discipline, and construction) to eliminate the factors of recognition:


  • Siting. Siting means selecting the most advantageous position in which to hide a man, an object, or an activity.
  • Discipline. Success in any concealment effort is the strict maintenance of concealment discipline by both the unit and by the individual soldier. All activities should be avoided that change the appearance of an area or reveal the presence of military equipment. Laxness and carelessness will undoubtedly reveal a position. Tracks, spoil, and debris are the most common signs of military activity, which indicate concealed objects. Ensure new tracks follow existing paths, roads, fences, or natural lines in the terrain pattern. Do not end exposed routes at a position, but extend them to another logical termination. If practical, tracks should be brushed out, camouflaged, or covered. Spoil and debris must be covered or placed to blend with the surroundings. Artificial camouflage is added when the terrain and natural vegetation are such that natural concealment is not possible.
  • Construction. Adding natural materials to blend with the surrounding terrain augments this type of concealment.
  4-6. There are three fundamental methods of concealing installations and activities: hiding; blending, and disguising. They are explained as follows:

  • Hiding. Hiding is the complete concealment of an object by some form of physical screen. For example, sod over mines in a minefield hides the mines; the overhead canopy of trees hides the objects beneath from aerial observation; a net hides objects beneath it; a defilade position hides objects from ground observation. In some cases, the screen itself may be invisible. In other instances, the screen may be visible, but it hides the activity behind it.
  • Blending. Blending is the arrangement or application of camouflage materials on, over, and around the object so that it appears to be part of the background. For example, applying face paint to the exposed areas of skin; adding burlap, paint, and live vegetation to helmets and clothing to closely resemble or blend into the background. The same technique can be applied for equipment or structures.
  • Disguising. Clever disguises can often mislead the enemy concerning identity, strength, and intention, and may draw his fire from real assets. Therefore, the simulation of objects, pieces of equipment, or activities may have a worthwhile military significance. Rubber tanks, tents, and buildings filled with air can look like the real thing to an aerial observer.



4-7. The difference between concealment and camouflage is that concealment is using natural terrain to hide, and camouflage is constructing concealment. In addition to hiding equipment, detection can be avoided by using mud for glassy surfaces and unfilled sandbags over windshields (Figure 4-2). Camouflage is one of the basic weapons of war. The importance, the principles, and the techniques of camouflage must be completely understood. All personnel must ensure the effectiveness of all camouflage measures, and must maintain the strict enforcement of camouflage discipline.

Figure 4-2. Detection Avoidance.



4-8. Another type of passive air defense, damage-limiting, is also used for survival. The measures are an attempt to limit any damages if the enemy detects the position. If the enemy is to destroy any equipment, he is forced to do it one piece at a time. A unit should not be in a position to be put out of action with just a single attack. The same measures taken to limit damage from artillery attack are used - dispersion, protective construction, and cover.

  • Dispersion. Dispersed troops, vehicles, and equipment will force the attacker to concentrate on a single small target that will likely be missed. The wider the dispersion, the greater the potential is for limiting damage.

  • Protective Construction. The use of cover, natural or manmade, acts to reduce damage and casualties. Folds in the earth, natural depressions, trees, buildings, and walls offer damage-limiting cover, which should be sought out and used habitually. If deployment is in flat terrain lacking cover, digging in or sandbagging can offer some protection. Smoke is used if the unit is moving and cannot use natural cover or cannot build fortifications. Smoke makes target acquisition much more difficult for the attacker.
  • Cover. The intent here is to emphasize the importance of passive defense against an air attack. Everything must be done to avoid an attack in the first place. Not succeeding in that aim, then cover and dispersion should be used to limit the amount of damage to the unit.



4-9. A convoy is vulnerable to air attack since it is easily seen from the air. Movements along a road are endangered by shoulders, ditches, and embankments which restrict freedom of maneuver. Additionally, since vehicles are stretched out in a long line, convoys represent high-value, hard-to-defend, but easy to hit targets to enemy ground attack aerial platforms. This linear array also makes command and control very difficult. A high probability of air attack must be assumed in planning a convoy, and all soldiers must know exactly what to do if attacked. Not all convoys will be provided dedicated air defense assets. Some convoys must rely on organic passive and active air defense measures for protection. As in defended areas, passive air defense includes attack avoidance and damage-limiting measures.



  4-10. Reduce the visible signature to the point where the enemy cannot find the convoy. While it is not possible to become invisible, every step taken in that direction decreases the likelihood that the convoy will be spotted. Not much can be done to change the shape of a vehicle moving down the road, but the type of cargo being transported can be disguised or concealed by covering it with a tarp. By rigging tarps and bows over the cargo compartment, the nature of the cargo can be concealed from the enemy pilot. Other effective passive measures are -
  • Train operators, as they disperse, to look for a bush, tree, or some other means of concealment to break their vehicles' shapes as seen from the air.
  • If vehicles are not already painted in a pattern to blend with the terrain and to break the outline, use mud, camouflage nets, or cut vegetation to achieve this effect (see FM 20-3).
  • Try to reduce the dust clouds that almost always accompany a convoy. If possible, try to avoid unpaved secondary roads. Reduce speed to reduce dust on unpaved roads.
  • Try to eliminate glare by using mud, tape, cardboard, tarps, camouflage nets, or ponchos to cover headlights, window glass, and other glossy surfaces. See Figure 4-3.
  • Use smoke or other obscurants to conceal positions and movements to deceive the enemy as to mission and intent (draw attention to deception operations).
  • Operate during periods of limited visibility as much as possible.
  • Position vehicles and facilities inside woodlines and erase vehicle tracks left outside woodlines.

Figure 4-3. Eliminate Glare.



4-11. A convoy is highly visible, and you should plan the convoy to limit damage in case your signature reduction efforts are not successful. Cover is the best damage-limiting factor.



Select Natural Cover


4-12. Ditches and embankments to the sides of the road offer cover and should be used if the unit is attacked. See Figure 4-4.

Figure 4-4. Selecting Natural Cover.



4-13. One of your better damage-limiting measures is the use of dispersion to lessen target density and reduce the lethal effects of the ordnance used against you. Most of the munitions that aerial platforms deliver against vehicles must make a direct hit to be effective. Dispersion decreases target density and thus reduces the lethal effects of enemy ordnance. The wider the dispersion, the greater the potential for limiting damage. Even area weapons become less effective if the unit is dispersed. The commander must weigh the need for dispersion against the need to stay concentrated to accomplish the mission. To achieve dispersion-


  • Travel in an open column with 80 to 100 meters between vehicles. Air guards will be posted throughout the column, constantly watching the skies in their assigned areas, ready to give early warning of a detected hostile aerial platform. The sooner a threat aerial platform is detected, the more time you will have to react. Air guards will search and scan for approaching aerial platforms, observing their assigned sectors. Alert the vehicle commander after sighting an aerial platform by calling out "plane" and pointing to the aerial platform.
  • Divide a convoy into small units or about platoon size and send the units out separately with at least 1,000 meters between units. This procedure provides a smaller target and increases the level of control over each convoy element.
  • Do not park vehicles in a straight line; instead, stagger the vehicles to present a poor target. Park the vehicles under cover if available. Make arrangements with the drivers so that if an attack occurs, they can drive the vehicles to the opposite sides of the road to seek cover. For example, the lead vehicle (odd numbered) is driven to the left, the second vehicle (even numbered) pulls off to the right, and so on (Figure 4-5).

Figure 4-5. Vehicle Dispersion.

Protective Construction and Use of Cover and Smoke/Obscurants


4-14. The use of cover (natural or manmade) reduces the probability of detection, damage, and casualties. Cover can prevent the projectile from striking the target. It reduces the target area exposed to damage, and it absorbs part of the blow. Folds in the earth, natural depressions, trees, buildings, and walls offer damage-limiting cover and should be used whenever possible. Digging in or sandbagging can offer some protection. When moving or when natural cover is sporadic and fortifications cannot be built, use smoke for concealment. Smoke and other obscurants make target acquisition much more difficult for the air threat. They also defeat guidance and control of precision guided munitions. Smoke and other obscurants can be used to deny threat air the use of avenues of approach, LZs, DZs, air battle positions, and key terrain as navigational aids.

4-15. If a hostile aircraft or a flight of hostile aircraft passes over your convoy and does not attack the convoy, you will still disperse the vehicles to the sides of the road. Stagger the convoy and prepare to return fire in case the aircraft returns. If the aircraft attacks, everyone will choose the correct aiming point and fire upon command until the aircraft is hit or flies out of effective range. Small arms alone can give coverage (Figure 4-6).

Figure 4-6. Small Arms Convoy Coverage



4-16. In terms of vulnerability to air threats, a convoy of vehicles usually presents a lucrative target. Convoys are easily visible from the sky, and shoulders of a road, ditches, or embankments restrict their freedom of maneuver. The linear array of a convoy makes command and control difficult. Convoys are high-value, hard-to-defend, easy-to-see/hit targets for enemy air. The unit must assume there is a high probability of air attack when planning any convoy.




4-17. Use routes that offer natural concealment. Trees and the shadows they cast offer concealment. The shadows cast by mountain ridgelines in the early morning and late afternoon also provide concealment. When crossing open country, travel should occur when the sun is high to avoid casting long, highly visible shadows. When possible, use multiple routes to reduce convoy lengths.



4-18. Travel in an open column with 100 meters between vehicles. Vehicles stretched out in a long thin line in a convoy are less of a target than vehicles that are close together.


  4-19. The convoy can also be broken into small platoon size units and dispatched separately with at least 1,000 meters between units (use separate march units). This procedure minimizes convoy size and increases the level of local control over each convoy element.



4-20. Make arrangements for an attack by moving the vehicles to opposite sides of the road to seek cover: The lead vehicle goes to the right, the second vehicle pulls to the left, and so on. This technique is called "Herringbone" (see Figure 4-7). If possible, have vehicles drive 45 degrees off the road and move to a covered and concealed position. Establish rally points for the convoy to reassemble after the attack. In cases where not all vehicles in the convoy have radios, the unit must develop a means to signal drivers that enemy aircraft are coming. The use of protective vehicle-launched or hand grenade smoke can cause the threat air to lose weapons lock or disrupt target acquisition long enough for convoy vehicles to find suitable concealed or dispersed positions.

Figure 4-7. Herringbone.


  4-21. Vehicles with weapons that are effective against air threats should be integrated into the convoy every fourth or fifth vehicle if possible. Many simple, commonsense measures can be taken by a unit to avoid attack and to limit damage if attacked. Units should plan for the use of, and make coordination for, the integration of MANPAD or SHORAD systems from general support or direct support ADA units whenever possible.


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