Air Fronts: Airdromes - FM-26, Defense of Airdromes - Chapter 5. Active Defense

SECTION I: GENERAL

35. BASIC PRINCIPLES.-a. The local ground defense of an airdrome is a relatively static defense of the runways or landing areas and vital airdrome installations, and a mobile defense of possible areas for the landing of airborne troops in the vicinity. The static defenses are located to cover the landing strips with heavy fire and to deny important avenues of approach. The location of the striking forces is dictated by the extent and location of other areas suitable for hostile landings and the routes of communication to them. Fixed defended localities are prepared for the mobile striking parties to occupy in the event that enemy forces are able to organize in large groups. These defended localities are located on key terrain points from which delaying action can be effected.

b. Antiaircraft artillery protection of forward area airdromes is of the utmost importance and must be considered both in planning airdrome installations and in planning the ground defense.

c. All planes should be put in the air as quickly as possible upon the approach of an enemy. They are parked to avoid unnecessary taxying, and crews are informed of the order of take-off. If simultaneous take-offs are possible, the direction of each plane is indicated by reference to markers on the field or features of the more distant landscape. A standing operating procedure designed to reduce last minute instructions to a minimum should be adopted and rehearsed. If attack is imminent, planes are periodically warmed up by ground crews or pilots.

SECTION II: ORGANIZATION OF THE GROUND

36. AREA OF DEFENSE.-The area to be defended is determined only after a careful estimate of the situation in which the terrain and the available forces are the dominant considerations. In most situations the maximum practicable objective is the security of adjacent terrain from which the airdrome can be rendered inoperative by aimed small-arms fire.

37. PRINCIPLES OF ORGANIZATION.-a. Sector defense.-Normally the local ground defense of an airdrome is a sector defense in depth. The area to be defended is subdivided by establishing sectors with a commander and troops designated for the defense of each. Sectors extend from a central point on the airdrome outward and provide cut-of-pie divisions of the area to be defended (see fig. 9).

b. Defense in depth.-Defense in depth is secured by a system of centers of resistance, gun positions, obstacles, road blocks, and fox holes planned for the delivery of covering fire upon important objectives and terrain. The inner defense positions should give mutual support. Outlying areas in the sectors are patrolled and defended by the sector defense forces. Reinforcement is provided for by mobile striking forces and by reserves formed from airdrome personnel.

c. All-around defense.-Whenever possible, defense positions are prepared for all-around defense.

d. Alternate positions.-In order to defeat enemy air reconnaissance alternate positions for weapons and men are dug so that the defense is flexible and elements can be shifted without loss of effectiveness.

FIGURE 9.-Sector defense.

e. Safety.-Plans of fire and movement must be prepared and executed so that friendly elements do not fire into each other. Such plans are particularly important in airdrome defense because airborne attacks may come from so many directions that friendly fire will be difficult to control.

38. RECONNAISSANCE.-a. Before other than emergency dispositions are made, a thorough reconnaissance of the terrain surrounding the airdrome should be undertaken. Detailed consideration should be given to the possibilities of attack under various conditions of time and weather. The defense commander should not be satisfied with initial dispositions dictated by obvious features of the terrain, but should plan such additional or alternate positions as will permit him to make best use of his forces when conditions change with the wind, the weather, the time, and the customs of the enemy.

b. Each place airborne troops can land must be determined, but shifts in the wind or changes in its velocity increase or decrease the natural hazard of an area for an enemy landing. Under certain conditions landings may be impossible in a given area. For dropping parachute troops with the minimum of casualties from the descent a fairly clear area 200 by 500 yards is required. Such a minimum space can not be used if the wind should be blowing perpendicular to its long axis, and the defense will consequently give it less attention than when the wind is blowing parallel to the long axis. Dispositions should constantly be shifted according to such changing circumstances. The direction and velocity of the wind and the state of the weather are important considerations in the plan for defense against any form of aerial attack. High winds may increase the hazard of dropping sufficiently to prevent the use of parachute troops altogether. On the other hand, high winds reduce the distance required for airplane landings and augment the number of potential landing sites. Low clouds and limited visibility may prevent the coordinated arrival of elements over the landing area and cut down the rate at which troops and supplies can be landed. The time of initiating and conducting operations will be determined largely by the weather forecast.

c. The enemy's customs of attack should be considered in making dispositions.

39. TYPES OF DEFENSE POSITIONS.-a. Centers of resistance.-(1) Key elements in the organization of the ground are strong centers of resistance. Each is provided with a supply of weapons, ammunition, food, and water and is capable of withstanding a short siege.

FIGURE 10.-Relation of direction of wind to choice of dropping areas.

(2) The principal mission of the inner centers of resistance is to deny the landing strips and adjacent open areas to the enemy. They are sited, preferably clear of the field, to cover the whole of the landing ground by fire of automatic or other weapons against parachute troops or aircraft attempting to land troops and to fire outwards if enemy troops penetrate the outer defenses. Some landing grounds can be adequately covered by one or two such centers of resistance; others may require four or five.

FIGURE 11.-Road block.

(3) The mission of the outer centers of resistance is to cover tactical features and approaches and broadly to serve as bases for the mobile defense. They are sited well clear of the airdrome. They may or may not be able to bring fire to bear on the airdrome itself. Some positions are for striking forces or reserves to occupy for delaying action in the event enemy forces succeed in organizing groups too strong to counterattack and will ordinarily be left unmanned or manned by a skeleton garrison. In conjunction with the major centers of resistance a number of small protected posts sited in the vicinity of the airdrome will be of value to counter the effect of parachute troops dropped over a wide area or to serve as a screen in the face of infiltrating attack. A tendency towards wide dispersion must, however, be curbed, as the enemy has the initiative and can concentrate superior forces at the point he chooses. Road blocks are placed to cut off easy routes of access.

b. Supplementary positions.-Well-camouflaged fox holes must be provided for airdrome personnel immediately adjacent to their places of occupation to compose a last line of defense for installations and grounded aircraft. Concealed positions are prepared clear of the target area for parties of backers-up ready to fight among the installations. Rallying points should be designated on or near the airdrome to which isolated parties or individuals will move if overtaken by air-borne attack while away from their units. Rallying points in the field, either prearranged or designated as needed, may be required. For these a system of visual or other signals is necessary. Field supply points are established in the de-fended area. Sufficient dispersion to insure rapid supply of units is necessary. Inflammable items should be stored separately. Observation posts with good communication are vital.

c. Command posts.-Command posts should be sited, preferably within a center of resistance, away from target areas. They should include splinterproof cover to contain telephone switchboards, map tables, shelter for runners and other necessary personnel, and limited sleeping accommodations. Alternate command posts must be provided.

40. FORTIFICATIONS.-a. General.-Fortifications will be, in general, field works-fox holes, open emplacements, splinter-proof cover, all well concealed and camouflaged. Elaborate fortifications of regular outline and raised parapets are targets for enemy action because of their regularity and obviousness on the aerial photograph. Fortifications must be sited with careful consideration to security from bombardment and the provision of all around supporting fire and covering fire for obstacles, tank barriers, and areas and approaches of strategic value. Alternate positions and dummies to attract fire are of great value. Field fortifications are covered in FM 5-15.

b. Fox holes.-Both the fox hole and the trench with some splinterproof overhead cover have their merits and uses, but the fox hole will be of most general value. All earth dug out must be removed from the site. If it is necessary to build up the fox hole, care must be taken that the work blends with the background so that when a man comes up to fire his head will not be silhouetted. A number of alternatives must be dug. Dummies can be put inside those not in use. A light lid with a covering of camouflage to match the surrounding ground should be fitted over each.

c. Pill boxes.-Pill boxes are of value for machine guns firing on fixed lines against troops on the ground, but they must be completely camouflaged and earthed up as much as possible. If possible, they should be proof against a direct hit by at least the equivalent of a 3-inch mortar.

d. Obstacles.--Tactical wiring is of great value and should be used in places where natural or other features give concealment from the air. It should follow vegetation, tracks, ditches, and the edges of broken ground. Under no circumstances must it be circular. The combat posts should be very completely and thoroughly protected with wiring adapted to suit the ground. Those which are manned by troops whose mission it is to sally out to attack landing air-borne troops or other troops must be wired so as not to delay exit. If wiring interferes with concealment, other protective devices, such as antipersonnel mines, must be substituted. In areas subject to mechanized ground attack antitank obstacles, primarily antitank mines, must be tied in with the defense. Construction of obstacles is covered in FM 5-30.

41. WEAPONS.-a. Machine guns.-(1) Machine guns are the basic weapons used in defense against parachutists, air-borne infantry, and ground troops. In a large measure their location will outline the defense plan. For defense against airborne attack the entire landing field and, to the extent possible, surrounding areas suitable for the landing of air-borne troops should be covered by machine-gun fire.

(2) The principles of distributing and siting machine guns for the defense of an area are covered in field manuals on infantry tactics (see FM '7-15, 7-20, and 7-40). The principle of distribution in depth should be emphasized even more than ordinarily in the defense of an airdrome because of the greater probability of airborne attack. Guns should be located in irregular mutually supporting groups with the view of eliminating as much dead space as possible. To make them effective at night, coordinated fires should be planned, final protective lines determined, range cards prepared, and firing stakes set out. In siting guns particular attention should be paid to stone or brick buildings within the area. If the number of guns permits, they should be sited in pairs, but in any event each emplacement should be prepared for all-around fire and all-around protection and should be fought as a little isolated center of resistance, since maneuver during attack may become impossible. The preparation of alternate and supplementary emplacements should not be neglected on this account.

(3) As most attacks on an airdrome will be preceded by bombardment, the area will be liberally pocked with craters, which will form convenient defiladed areas for enemy troops to escape flat-trajectory fire. Mortars may be supplemented by machine guns placed in position on high ground or buildings to deliver plunging fire upon defiladed positions.

(4) As many heavy machine-gun positions as possible should be prepared to permit the engagement of hostile aircraft. Suitable machine-gun targets are strafers, transport planes which have leveled off to discharge parachutists, gliders, fighter or bombardment planes protecting transports, and transports or gliders on the ground.

b. Mortars.-(1) Mortar fires are for the most part fires against personnel to cover dead spaces in the bands of machine-gun fire and defiladed areas where hostile forces might assemble for attack. Their positions must be within effective range and must afford observation of the targets and friendly troops from observation posts. As attacking forces, even parachutists, will be certain to have mortars in their armament, they are essential weapons for the defense of an airdrome subject to any form of infantry attack. They should be kept mobile.

(2) The 60-mm mortar is a highly mobile piece with a useful range of about 1,000 yards. The effective radius of burst of the high-explosive projectile is about 15 yards; casualty producing fragments carry much farther. It should not be located more than 500 yards behind friendly troops. Its low relief permits it to utilize the cover afforded by minor terrain features such as bomb craters, ditches, hillocks, or small rises.

(3) The 81-mm mortar combines mobility and power in greater degree than any other supporting weapon. Its projectiles have an explosive effect comparable to that of 75-mm projectiles. Its useful range is about 2,000 yards and its distance behind the farthest friendly troops should not exceed 800 yards.

(4) The principles of the employment of mortars are covered in FM 7-15, 7-20, and 7-40.

c. Antitank weapons.-(1) Direct-fire, high velocity anti-tank weapons are needed in the ground defense of forward airdromes. They are also effective against any observed targets such as machine guns, antitank guns, or landed air-craft. Antitank guns employ direct fire and engage only visible targets. Such characteristics indicate employment in close proximity to the troops or areas to be defended. Whenever possible, gun positions are selected in terrain which is unfavorable for tank operation but from which effective flanking fire may be delivered against favorable avenues of approach. In covering a road the gun should be sited to fire on a stretch where detour is restricted by ditches, banks, heavy woods, or similar obstructions. One well-placed antitank weapon can temporarily stop or delay a large mechanized force.

(2) The antitank rocket launcher is an electrically operated shoulder weapon weighing about 15 pounds and having a maximum firing rate of eight rounds per minute. Primarily it is used to fire upon hostile armored vehicles which come within effective range. The rocket will penetrate 3½ inches, or approximately 90-mm, of armor plate. Although normally considered an antitank weapon, it has other tactical uses, including the following:

(a) To increase the fire power of close-support weapons.

(b) To provide close-in defense of crew-served weapons.

(c) To deliver harassing fire against concentrations of personnel.

(d) To protect mine fields, road blocks, and wire entanglements.

(e) To protect observation and command posts.

(3) Antitank protection can also be provided by the guns of the antiaircraft artillery defense, the 40-mm gun being an excellent antitank weapon. When possible, without material interference with their primary mission, these guns should be sited for a secondary mission against mechanized vehicles.

(4) The principles of the employment of antitank guns are covered in FM 7-20, 7-35, and 7-40.

d. Field artillery.-The actual assignment of a battery or other unit of field artillery to the local defense of an airdrome is the exception rather than the rule. The successful employment, of field artillery in such a defense role demands the retention of full mobility. Field artillery should be disposed to cover the landing ground and so sited that it can fire on it over open sights from positions at some distance, possibly 1,500 to 2,000 yards, depending on the country. Possible approaches for mechanized ground forces should be carefully targeted. An important mission is bringing fire to bear on areas near the airdrome on which the enemy may be attempting to land transport planes. Even if landings have been successfully made, accurate fire can destroy enemy infantry in assembly positions forming for attack. Timed artillery fire is effective over troops digging in under cover of their automatic weapons.

e. Antiaircraft artillery.-See paragraphs 45 to 51, inclusive.

42. LOCAL SECURITY.-The danger of airborne attack increases the need for all-around and independent defense of units. Gun crews should be armed with rifles and supplemented with riflemen to provide for their own immediate defense. Light machine guns should be assigned to the local protection of antiaircraft and artillery pieces. All posts and detachments should be supplied with reserves of ammunition, food, and water.

43. MOBILE DEFENSE.-a. Striking forces.-Striking forces must be available to attack parachute troops and air-landing troops at the earliest possible moment, to counterattack hostile forces, and to come to the relief of parts of the static defense if they are in danger of being overrun. They should be assigned to covered and concealed positions off the airdrome where they will not be exposed to the preliminary bombardment. They must be located near probable places of commitment, as during attack the enemy can be expected to strafe thoroughly all troop movements. They should be supplied with such transportation and weapons as will give them mobility and high fire power. They should be provided with entrenched positions into which they can withdraw for delaying action if the enemy succeeds in organizing concentrations too strong for them to attack. Normally they are an integral part of the sector defense to which they are assigned.

b. Reserve striking force.-A mobile striking force must be held in reserve for employment against enemy concentrations which are too strong for the sector forces. It must be concealed off the airdrome. It is provided with such armor, troop carriers, scout cars, and mobile guns as are available. It is normally under the immediate control of the defense commander.

c. Armored vehicles.-To reinforce threatened points and to break up concentrations of hostile troops, armored vehicles, preferably tanks, should be available. Because of the cross-country mobility of tanks and armored half-tracks, their high fire power, and, in the case of tanks, their adaptability to crushing tactics and the protection they afford personnel, a few of them can be of decisive value.

44. COMMUNICATIONS.-a. General.-The importance of adequate communications cannot be overstressed. During the crucial moments of the defense of an airdrome time is so short and the situation so fluid that there can be no delay in executing the proper actions. All detached posts must be in touch with the command post. Telephone may be used for all fixed installations, but radio is essential for units used as striking forces.

b. Alternate means of communication.-Visual or audible signals may become the only means of communication available for the command. A system of such signals should be carefully thought out and learned. The institution of a simple code for likely battle orders and information helps to overcome the complications of training the number of signalers required.

c. Radio jamming.-During an attack the enemy may attempt to jam the radio communication of the defense by transmitting blurring signals on defense frequencies. Preparations and instructions issued in advance will help maintain confidence and morale when jamming is attempted. Such precautions may include

(1) Preparation of a scheme for changes in frequency when jamming is encountered.

(2) Transmissal of messages on several frequencies.

(3) Authentication of incoming messages. (It is likely that the enemy will intersperse jamming with false messages.)

SECTION III: ANTIAIRCRAFT DEFENSE

45. REFERENCES.-The details of antiaircraft artillery defense are found in FM 4-100, 4-102. 4-104, and 4-106.

46. GENERAL.-Air forces normally have antiaircraft artillery assigned or attached for the protection of operational airdromes. The antiaircraft artillery defense of an airdrome may include both guns and automatic weapons, but the local defense of forward-area airdromes consists ordinarily of automatic weapons. The antiaircraft artillery commander coordinates his fields of fire, emplacements, camouflage discipline, and communications with other airdrome defense troops and with the airdrome commander. It is particularly important that plans be prepared for the movement of friendly aircraft in the vicinity of the airdrome, for inter-communication between aircraft in flight and elements of the antiaircraft defense, and for recognition of aircraft.

47. MlSSION.-The mission of antiaircraft artillery employed in airdrome defense is threefold

a. To defend the airdrome and its installations against air attack by destroying enemy aircraft, causing them to abandon their mission, or disturbing their actions to such an extent that they miss the target.

b. To defend the airdrome against attack by airborne troops by fire action prior to the landing,

c. To assist airdrome defense units by antimechanized fire and supporting fires on ground objectives.

48. DEFENSE OF FORWARD-AREA AIRDROMES.-a. General.-Defense must be sited in depth so that attacks on the perimeter of the airdrome will not necessarily eliminate the anti-aircraft defenses. Weapons must be sited to bring maximum fire on all enemy aircraft, whether attacking simultaneously or in succession, before hostile acts are committed. Each defense must be constructed to meet the prevailing or indicated types of hostile action. Actual field disposition of fire units is adjusted to meet local conditions.

b. Employment of automatic weapons.-(1) Targets.-Primary targets of automatic weapons are hostile low-flying aircraft-low-altitude bombers, dive bombers, strafers, troop carriers, and gliders. Automatic weapons also have a secondary mission in antimechanized defense and the provision of supporting fire against ground and water-borne targets.

(2) Range.-The effective slant range of the 40-mm gun is taken as 1,500 yards.

43) Dispositions.-As a rule, an automatic weapons defense will be provided to combat only low-altitude horizontal flight bombardment attack and ground strafing against the airdrome itself. Additional fire units are disposed to extend the defense in depth and to reinforce the defense, particularly along the more probable avenues of approach. For defense against horizontal flight attack, automatic weapons are placed at or near the bomb release line corresponding to the altitude of the attack. Against dive bombardments, units are sited as near the objective as possible although not so close that attacks on the object will put the guns out of action or blind them by dust and debris from the explosives. This indicates that guns sited for defense against dive bombardment attacks should be located 300 to 500 yards away from the objective.

(4) Coordination of fire.-Coordination of fire must be achieved. The dead areas of the guns are coordinated so that all avenues of approach will be covered by gun fire. To insure efficient engagement of all targets, normal and contingent zones of fire are specified for each firing unit. Fire direction is exercised by the fire unit commander subject to general directions from higher authority concerning such matters as withholding fire and priorities of targets and specific orders to coordinate with friendly air force operations.

(5) Examples.-(a) Fighter strip defended by one platoon of automatic weapons.-The four fire units are emplaced on the central axis of the strip, one at each end, and the other units 500 to 800 yards out. (See fig. 12.)

FIGURE 12.-Short strip defended by one platoon of automatic weapons.

(b) Fighter strip defended by one battery of automatic weapons.-The defense is formed by adding to the four-unit defense shown in figure 12. The additional four units are set out approximately 500 yards to each flank of the outermost guns. (See fig. 13.)

FIGURE 13.-Short strip defended by one battery of automatic weapons.

(c) Bomber strip defended by 12 automatic weapons fire units and two 90-mm gun batteries.

1. Automatic weapons.-The length of a 7,000-foot strip will cause the automatic weapons to be out of supporting distance of each other if the method of emplacing used in (a) and (b) above is employed. The fire units are arranged in a ring 500 to 800 feet from the perimeter of the landing strip. (See fig. 14.) Dead areas are coordinated as shown so that an adjacent gun covers the dead area of each gun.

2. Gun batteries.-At altitudes above 2,500 feet the approach most favorable to the bombers is perpendicular to the strip. The gun batteries are placed 2,500 to 3,000 yards out from the center of the strip perpendicular to its length. (See fig. 14.)

FIGURE 14.-Antiaircraft artillery defense of a bomber strip.

49. RESTRICTIONS.-a. The following are some of the restrictions that might be imposed on fire:

(1) Any unit may fire, unless specifically restricted.

(2) Fire units not specifically prohibited from firing may fire on any airplane entering their field of fire unless it is definitely identified or recognized as friendly.

(3) Fire units may take under fire any airplane entering their fields of fire except those flying in definite channels of approach or definitely identified or recognized as friendly.

(4) Any airplane committing a hostile act may be taken under fire.

b. All personnel must be thoroughly trained in visual recognition.

c. Restrictions on opening fire will be placed in effect by the airdrome commander. Control is exercised through the antiaircraft artillery commander. Restrictions imposed on fire are normally the minimum consistent with coordination of the air defense and to insure the safety of friendly aircraft.

50. LOCAL AIR GUARDS.-All fire units must be protected by local air guards. (See par. 79.) Guards must be provided with means of communication for transmitting warning of approaching planes.

51. SMALL-ARMS FIRE AGAINST AIRCRAFT.-a. Properly delivered small-arms fire is an effective method of counter-attacking low-flying airplanes. Its effectiveness depends upon the training of personnel and upon their constant alertness. The result of small-arms fire upon aircraft is not to be measured only by the count of planes actually brought down. Damage to radio, mechanical, and electrical systems is frequently inflicted by rifle and machine-gun bullets which, though it may not prevent the plane from returning to its base, necessitates extensive repair. Damage caused by the passage of a bullet through a wing or control surface requires repair work that may prevent at least one operational flight. There is also an important effect upon the morale of troops employing their weapons against low-flying aircraft.

b. FM 21-45, 23-5, 23-6, 23-7, and 23-10 explain the technique of directing small-arms fire against aircraft.

SECTION IV: PERSONNEL

52. GENERAL.-a. All troops stationed at an airdrome will be considered available for its defense when needed. The order of availability will be the following: ground defense troops; aviation engineer troops; chemical warfare service decontamination troops and other service troops; Army Air Forces troops whose mission is administration or operation, maintenance, and repair of aircraft; and other troops within supporting distance. All personnel should have some defense duty assigned and be drilled in its performance. All personnel not actually engaged at the moment in the maintenance or operation of aircraft must be prepared to engage in the fire fight.

b. All personnel must keep gas masks, weapons, and ammunition close at hand. When the alarm sounds they will report to previously designated assembly areas, armed and ready for combat.

1 53. FIXED DEFENSES.-In general, armed airdrome personnel should man less vital static defenses in order to free garrison troops for mobile operations. Such posts can be left partially manned or unoccupied until the ground defense is placed on the alert. It is necessary, however, to have certain defensive positions manned continually. Antiaircraft weapons must always be ready to fire, as must, to a lesser extent, antitank weapons on likely routes of approach and machine-gun posts in vital areas. For all such assignments, no reliance initially should be placed upon men who have a full-time job that will demand their presence at another part of the airdrome. Airborne attacks develop too rapidly to permit them to man posts at any distance. Available airdrome personnel can be employed to reinforce centers of resistance. Dispersed personnel should be employed to create small islands of resistance near their place of employment. This practice will establish a series of garrisoned points to form a defensive zone that will limit the movements of enemy troops who break through or land on the airdrome itself in order to attack special installations.

54. STRIKING FORCES AND RESERVES.-a. Striking forces should be composed of troops especially trained for ground defense. Enemy airborne units may be expected to consist of troops who have received special training. Defensive units sent against them should consist of troops of corresponding caliber.

b. A final reserve can be formed from air force troops who have formed at assembly points at locations where the larger numbers of air force personnel are occupied.

SECTION V: EMPLOYMENT OF THE DEFENSE

55. GENERAL.-Successful defensive tactics are based on adequate security measures and proper use of fire and maneuver. A proper evaluation of the terrain and an estimate of the situation are of first priority. Based on these, the defense is planned in accordance with established infantry and antiaircraft tactics.

56. MINIMIZING EFFECTS ON BOMBARDMENT.-a. Before an attempt at airborne or ground attack, bombardment and strafing will normally be directed at defense and operational installations, at the outlined perimeter of the field and along the edges of surrounding woods, at housing areas, and at any location that suggests a remunerative target. Special defense forces can survive only by keeping under cover in concealed locations in the vicinity of the airdrome but not on it or its perimeter or in any place the enemy may be anticipated to suspect and bomb because of its aptness for concealment.

b. During the initial bombardment machine guns and other guns sited for ground defense normally remain concealed and reserve their fire for their primary targets. Like-wise under certain conditions some of the antiaircraft weapons may remain silent. Preliminary bombing or strafing runs are often made with small force to provoke the defense into revealing dispositions.

57. ALERTNESS.-Alertness is the first essential of defensive operations. At all times, even during the height of a bombardment, some men must be on the lookout to guard against surprise.

58. OBSERVATION SYSTEM.-For proper employment of the defense it is essential the defense commander have a spotting system for accurately identifying danger points. The system should include observation posts and patrols. (See par. 79.)

59. PATROLLING OUTLYING AREAS.-It is ordinarily not within the resources of the defenders to place combat groups at all possible landing places for airborne troops. The more distant of the probable landing areas should be patrolled.

▪60. IMMOBILIZATION OF MOTOR VEHICLES.-Plans should be made for quick immobilization of all vehicles which cannot be kept from falling into enemy hands. Immobilization can be surely attained only by the removal of some major part or by wrecking. The same part must be taken from all vehicles to prevent the use of parts from some vehicles to make others operative. The attackers, even parachute troops, may be expected to come provided with various sizes of spark plugs, gaskets, hose joints and clips, distributor parts, wire, batteries, nuts and bolts, flexible tubing for gasoline and oil lines, hacksaws, screw drivers, hammers, chisels, spanners, and adjustable wrenches. The quickest method of destruction is by rifle and machine-gun fire on vital parts, including tires. The most satisfactory method, when time permits, is by the use of explosives.

61. PRINCIPLES OF ACTION AGAINST AIRBORNE TROOPS.-a. Nature of action.-The nature of the action against air-borne troops is such that once a defense unit is committed, its commander must act largely upon his initiative. The combat will normally develop into a series of independent action to capture or destroy small groups of attackers before they can organize.

b. Advantages of the attack.-Airborne troops, particularly parachute troops, have a definite advantage over the defender in that the area selected for landing may be anywhere within a wide range and that the actual location and time of the landing can be kept secret until the descent is begun. Several landings can be made simultaneously to place the defense at the further disadvantage of uncertainty as to where the main effort of the attack is to be made. Under the threat of reinforcing immediate successes, the attacker can force the defense to disperse its forces or perhaps tempt it to improper use of them. In effect, the defense must guard against the sudden advent of the fire power and holding power of hostile infantry within its own lines.

c. Advantages of the defense.-(l) Until they are organized on the ground, airborne troops are dispersed and lightly armed infantrymen hampered by the necessity of freeing themselves from parachutes, gliders, or transports and of collecting and assembling weapons or unloading them. During the first few minutes after their arrival they can be destroyed by a fraction of the number of defenders.

(2) For about 30 seconds before the jump, a transport plane loaded with parachute troops levels off at a low altitude and flies a straight course toward the landing area. As it takes about 10 seconds for a squad and its equipment to be discharged, the transport is flying slowly along a straight course for a total period of about 40 seconds, an easy target. Parachutists are practically helpless during their descent and in the period immediately following their landing when they must collapse their parachutes and get out of their harness. Materiel containers must then be located and unpacked and the squads or larger units must assemble. As the landing pattern of a squad is large, its average length being about 400 yards, assembly takes an appreciable period of time.

(3 ) Gliders are extremely vulnerable if they come low over hostile troops. As their flight is very slow, the troops they carry can be destroyed before the landing. Fire directed at the forward part may reach the pilot and cause the glider to crash. Landings on bad ground, even if the glider is not smashed, may temporarily shock or stun the troops.

FIGURE 15.-Parachute troops landing.

d. Employment of heavy weapons.-The necessity for rapid entry into action against airborne troops dictates that heavy weapons be located in firing positions. Artillery is normally limited to direct fire. Its primary targets are gliders or transport planes halted or moving slowly on the ground.

e. Time of opening fire.-Time of opening fire is controlled to conceal the locations of weapons and organizations until they can be employed with best effect. Outguards open fire on transport planes and parachutists as soon as they are within range and maintain intensive fire. The reserve elements in concealed areas hold their fire until they are committed to action or are directly in the path of descending troops. Heavy weapons normally open fire on appropriate targets of opportunity as they arrive within suitable range. Some antiaircraft weapons may remain silent to deal with the main attack when it develops. When transport planes come in for a landing, the defender must be ready with fire-power and the maximum possible surprise to inflict heavy casualties on the initial landing party.

f. Counterattack.-(1) Regardless of antiaircraft fire, in any airborne attack of force some troops must be expected to effect a landing. The defender must attack and destroy them before they can assemble and develop an effective force. Landing fields and other vulnerable areas can best be protected by fast-moving hard-hitting striking forces equipped with automatic weapons capable of high-angle fire, light cannon, armored vehicles, and transportation which can destroy the attacker before he completes his landing or organizes on the ground. Later counterattacks should be under-taken only with strong fire support and by the methods which would be necessary against any other ground force. The character of action by the airdrome defenders, however, must be offensive, and time is the element of greatest importance.

(2) Parachute troops must be attacked immediately. If parachutists land close by, it is essential that the personnel of even small defense posts sally out to attack them with automatic weapons, grenades, rifles, and bayonets. A small, determined force can cope with several times its number of parachutists if it attacks the instant they hit the ground. For 30 seconds after landing parachute troops are quite helpless, for 2 minutes they are more or less helpless, and for the 3 to 5 minutes it requires for them to begin organizing and digging in they are very vulnerable. If they are not destroyed during this time, reserves must be committed in sufficient force to isolate or destroy them before they can organize into larger units and move on vital areas for completion of their mission or before they can be reinforced. It must be expected that forces moving to the counterattack will be strafed by the enemy's supporting aviation. Troops constantly need to take advantage of cover to minimize the effects of the fire of the enemy's aircraft. Successful counterattacks may be turned into failure if the attackers do not find cover before being counterattacked in their turn by hostile aircraft.

(3) Armored vehicles are of the utmost value in the counterattack. They should be concealed in relatively safe positions during the preliminary bombardment and brought into action during the critical stage of the ground action which may subsequently develop. They must be regarded as striking units and must not be employed in a static role in lieu of fixed defense posts to cover any predetermined areas or any particular approaches. Their primary mission is offensive action to cause as many casualties, as much damage to equipment, and as much confusion among landed troops as possible. They must not be allotted such tasks as carrying messages or hunting down parachute troops dispersed individually over the countryside. After delivering their attacks they should be withdrawn and held in reserve to meet further threats.

FIGURE 16.-Tanks attacking parachute troops.

Because of their speed, armor, fire power and weight, tanks are especially valuable for attacking parachute troops as they land. While parachutists are struggling with their harness, tanks should cruise among them, crushing them and their equipment. Half-tracks should not come close enough to be the targets for hand grenades. Their loads of troops should get out and attack as skirmishers or dig in for holding fire. Scout cars may be used to screen the movement of a striking force to a threatened area. Rifle troops should follow closely behind armored vehicles. These troops should, if possible, be moved by truck close to the area of initial employment. Personnel carriers may be used to transport small combat groups to the attack of enemy positions.

(4) Some members of a counterattacking force must be detailed to collect or destroy arms containers and their contents or, in haste, to hide their distinctively colored parachutes. All personnel should give special attention to any parachutes of a color in a minority, as they may mark weapons, officers, rallying points, etc. If there is any wind, arms containers may be dragged down wind by their parachutes. Movement in this direction will insure early contact with parachutists and facilitate the capture of their equipment. Every effort should be made to confuse supporting aircraft by firing captured Very pistols and laying out captured signal strips and flags. Patrols should be sent out to capture supplies dropped at later periods or to cover them with fire, but striking forces and reserves should not be weakened during the attack on the airdromes to supply details to mop up small isolated groups of parachutists who may have dug in. These elements should be disposed of in detail later.

g. Feints.-A parachute attack will probably be accompanied by feints. Dummies may be dropped at one place and the troops for the attack at another. It must therefore be quickly determined in every instance whether dummies or troops are being dropped. Dummies hit the ground hard and bounce. If there is even a slight wind, they are pulled along lifelessly by the parachute. The difference most visible from a distance is the absence of efforts like those made by parachutists to control their descent. Unless the terrain is free of obstacles, genuine parachutists will be observed maneuvering their parachutes to land in a favorable place by twisting their bodies and pulling their shroud lines as they near the ground.

h. Interference with communications.-The success of an airborne attack depends largely upon radio and visual communications. In the early stages of the operation the reports received at enemy headquarters from reconnaissance air-craft are the basis for determining detail of subsequent operations. In the later stages information must be had from units on the ground by means of radio or visual signals. It may be possible to jam the enemy's radio traffic with good results, and his visual signals can be copied and repeated to his confusion.

i. Plans for action.-The details of the execution of a general plan of action against airborne troops (see par. 105 and 106) cannot be evolved until actual dropping or landing has begun and it becomes possible for the defenders to discern the enemy's intentions. Each unit commander, however, should attempt to anticipate the various forms the attack might take in the area assigned to him and prepare a plan for each imagined possibility. Any plans given to the troops should be simple and flexible and not tied down unalterably to geographic localities, as it cannot be foreseen where the enemy will drop his troops or land his gliders or that he will succeed in placing them where he wants to place them. The important factor is that his troops are extremely vulnerable immediately after landing; consequently, it is the aim of the defense to conserve its strength until the enemy is on the ground and then to attack vigorously no matter how badly it may appear to be outnumbered. Each commander must visualize exactly what he is going to do in each contingency during the few critical minutes most favorable to his success. Counterattacks should be rehearsed by troops assigned to the sector.

62. DELAYING ACTION.-It is probable that the forces available for the local defense of the airdrome will be consistent with the battle situation in the area. The local ground defense is normally a delaying action fought to hold the airdrome or to deny its use' to the enemy until supporting forces in the area can come up.