Military

a.   On the offense. During offensive operations periodic halts may be required to regroup, resupply, or consolidate positions gained. Where the enemy threat is known to include a counterattack capability (or probability), offensive units should seek available cover should dig hasty emplacements.

b.   On the defense. A defensive position is built round a series of organized and occupied tactical positions. Positions are selected for their natural defensive strength and the observation afforded. Fortification measures include clearing fields of fire, digging weapons emplacements and positions for personnel, strengthening natural obstacles, installing artificial obstacles, and providing camouflage.

c.   Fortification plans. Plans for fortification not only provide for the desired degree of protection but also for bringing the enemy under the maximum volume of effective fire as early as possible. Fortification plans are usually based on progressive construction, that is, proceeding from open to covered emplacements and shelters, to the ultimate protection permissible under the circumstances. Characteristics of personnel and individual weapons emplacements are shown in table 1-1.

d.   Dispersion. The separation of units and individuals is a primary means of protection, particularly from the effects of nuclear weapons. If the area occupied by a unit is doubled, it is less vulnerable to shell fire or the effects of nuclear weapons. Proper dispersion can greatly reduce the requirements for high level protection from field fortifications. The amount that a unit spreads out depends on the mission, terrain, and the enemy situation. Fortifications, properly employed, can be used in lieu of, or to supplement, dispersion, but fortifications are particularly important for units that cannot disperse sufficiently to obtain adequate protection.

e.   Alternate and dummy positions. When time and the situation permit, dummy and alternate positions should be constructed to deceive the enemy and to allow flexibility in the defense.

a.   Employment of weapons. Emplacements must permit effective use of the weapons for which they are designed. This requirement may limit the protection which can be provided and may influence the design and depth of adjacent shelters.

b.   Protection. As far as possible, protection should be provided against hazards except a direct hit or a close nuclear explosion. To obtain maximum protection, excavations should be as small as possible, thereby limiting the effective target area for high trajectory weapons and airbursts.

c.   Simplicity and economy. The emplacement or shelter should be strong and simple, require as little digging as possible and be constructed with materials that are immediately available.

d.   Progressive development. Plans for defensive works should allow for progressive development to improve the usefulness of the fortification. Development fortifications can be accomplished in three steps—

e.   Camouflage and concealment. Fortifications should be built so that the completed work can be camouflaged. It may not be practical to conceal a defensive position completely, but it should be camouflaged enough to prevent the enemy from spotting the position by ground observation. If possible, dummy positions should be constructed the same time as the actual position.

f.   Ingenuity. A high degree of imagination and ingenuity is essential to assure the best use of available materials as well as the best choice and use of the fortifications constructed.

a.   Digging in. Protection against conventional weapons is best provided by constructing a thickness of earth and other materials. This is done by digging into the ground so that personnel and equipment offer the smallest target possible to the line of sight of weapon. This means of protection is effective against direct fire of small arms and horizontally impelled shell fragments. Digging in also provides some protection against artillery, infantry heavy weapons, bombs, and other serial weapons. Advantage should be taken of all available natural cover. Improvement of the position continues until the unit leaves the area.

b.   Overhead cover. Overhead protection is important particularly in the forward areas where the threat includes airburst shelling in addition to the possibility of nuclear attack. Covered firing positions should be built for individual riflemen. Small readily accessible shelters adjacent to weapons emplacements are also necessary. A minimum of 15-20 centimeters (6-8 inches) of logs, 45 centimeters (18 inches) sandbags, rocks, and dirt, in that order, is required for overhead protection. Any available material may be used but cover should be kept low. However, cover of this type will not protect personnel against direct shell hits. Overhead cover should be strengthened and improved as long as the position is occupied. Only part of the firing position should be covered. Sandbags are placed over the logs to prevent dirt from falling on the occupants.

a.   Radiation. The presence of radiation and the high intensity of the blast or earth shock following nuclear explosions distinguishes them from the effects of conventional bombs or other explosives.

b.   Blast and earth shock. Blast and associated earth shock effects are caused by violent changes in pressure that move out in all directions from the center of the explosion, like a very strong wind. Most direct injuries from the blast effects result when personnel are thrown to the ground by the blast. Indirect blast injuries are sustained from flying debris and the collapse of emplacements, shelters, trenches, or buildings.

a.   Before the explosion. If there is warning of a nuclear explosion, and available time and the tactical situation permit —

b.   During the explosion.

c.   After the explosion.

a.   Friendly nuclear weapons. Nuclear weapons may be used close to our own areas. If used close enough to be dangerous there will be warning and instructions on precautions to take. The individual protective measures discussed above are important in a situation of this kind.

b.   Contaminated areas. If required to occupy a contaminated (radioactive) area, the following actions should be taken:

c.   Contaminated equipment. Trained personnel in each unit will use instruments to test equipment and supplies for contamination. If instruments are lacking, the urgency of the situation dictates whether equipment is used without being tested. Generally, equipment not damaged by the explosion is safe to use. Washing or brushing will usually make contaminated equipment safe to operate.

a.   Natural. Full use is made of all available natural materials such trees, logs, and brush in constructing and camouflaging emplacements, shelters and overhead cover. Usually, enough natural material can be found to meet the requirements for hasty or expedient fortifications. Snow and ice may be used in the construction of emplacement and shelters in cold regions.

b.   Other materials.

a.   Handtools. The individual soldier is equipped with an intrenching tool and, if necessary, he can use his bayonet to assist in digging. Pick mattocks, shovels, and other tools are also useful, and frequently available for this purpose (fig 1-1). In addition, captured enemy equipment may be available. The relative value of each tool depends on the soil and terrain. In arctic areas, a larger quantity of picks and pick mattocks are required to aid in the preparation of emplacements in frozen ground.

b.   Equipment. Relatively narrow cuts with steep or nearly vertical sides required for most emplacements or shelters can be excavated more accurately by hand. However, intrenching machines, backhoes, bulldozers, bucket loaders, and scrapers may be where the situation will permit the use of heavy equipment. Usually, these machines cannot dig out the exact shape desired or will dig more earth than necessary, requiring completion of the excavation by hand. Additional revetment material is usually required when machines are used. Distinctive scars on the ground resulting from the use of heavy equipment require more effort for effective camouflage than fortification work performed by hand.

c.   Explosives. Many fortification tasks are made easier and accomplished more quickly by using explosive in any type of soil. Special explosive digging aids available include the M2A3 and M3 shaped demolition charges, and the field expedient det cord wick.

a.   Hasty emplacements. Hasty emplacements are dug by troops in contact with the enemy, when time and materials are limited. Hasty positions should be supplemented with overhead cover and strengthened as conditions permit. If the situation permits, the small unit leader will verify the sectors of observation and fire for the individual members of the squad from their designated positions before they dig individual foxholes. When the situation is stabilized, even temporarily, positions are selected so they can be connected by trenches later. The emplacements described below provide protection against flat trajectory fire. They are used when there is no natural cover. Hasty positions (figure 1-2) are good for a short time because they give some protection from direct fire. If the unit remains in the area, they must be developed into well-prepared positions to provide as much protection as possible.

b.   Foxholes. Foxholes are the individual rifeman's basic defensive position. They afford good protection against enemy small arms fire and can be developed from well chosen craters, skirmisher's trenches, or prone emplacements. Foxholes should be improved, as time and materials permit, by revetting the sides, adding expedient cover, providing drainage, and excavating a grenade sump to dispose of handgrenades tossed into the hole by the enemy.

Figure 1-6.   One-man foxhole.

Figure 1-7. Camouflaged one-man hole.

Figure 1-8.   One-man foxhole with half cover.

Figure 1-9.   Types of revetting material.

Figure 1-10.   Supporting and anchoring revetment.

Figure 1-11. Open two-man foxhole.

c.   Full frontal berm overhead rifle positions.

Figure 1-12.   Two-man foxhole with offset.

Figure 1-13.   Two-man foxhole with offset constructed of timber and culvert.

Figure 1-14.   Rifle position.

Figure 1-14. Rifle position (Continued)

Figure 1-15. Overhead cover for foxhole (fabric).

a.   Principles. There is little opportunity to clear fields of fire when a unit is in contact with the enemy. Individual riflemen and weapons crews must select the best natural positions available. Usually, there is only time to clear areas in the immediate vicinity of the position. However, in preparing defensive positions for expected contact with the enemy, suitable fields of fire are cleared in front of each position. The following principles are pertinent:

b.   Procedure.

a.   Firing positions. While it is desirable to give maximum protection to personnel and equipment, the principal consideration must be the effective use of the weapon. In offensive combat, infantry weapons are sited wherever natural or existing positions are available or where weapons can be emplaced with a minimum of digging. The positions described in this section are designed for use in all types of terrain that will permit excavation.

b.   Protection. Protection of crew-served weapons is provided by emplacements which give some protection to the weapon and crew while in firing positions. As the positions are developed, the emplacements are deepened and provided with half overhead cover, if possible. Then, if the positions are occupied for an extended period of time, shelters adjoining the emplacement or close to it should be built. Characteristics of crew served infantry weapons emplacements are shown in table 1-2.

c.   Crew shelters. Shelters immediately adjoining and opening into emplacements improve the operational capability of the crew, since the men are not exposed when moving between the shelter and the weapon.

a.   Pit type. The gun is emplaced initially in a hasty position (fig. 1-18).

b.   Horseshoe type. The dimensions and layout of the completed emplacement are shown in figure 1-19. The horseshoe shaped trench, about 60 centimeters (2 feet) wide, is dug along the rear and sides, leaving a chest-high shelf in the center to serve as the gun platform. The spoil from this trench is used to form the parapet, making it at least 1 meter (40 inches) wide and low enough to permit all-round fire. This type emplacement permits easy traverse of the gun through an arc of 180°, but the crew cannot fire to the rear effectively. The firing table must be reverted to prevent the vibrations of the automatic weapons from breaking down the walls of the table.

c.   Two one-man foxhole type. This emplacement consists of 2 one-man foxholes close to the gun position as illustrated in figure 1-20. The parapet is low enough for all-round fire and good protection for the crew, A foxhole is dug for the gunner at the rear of the gun and another foxhole is dug for the assistant gunner on the left of the gun and 45 cm (18 in.) in front of the gunner's foxhole. The spoil is piled all around the position to form a this position, fire to the front or rear is most effective since the M60 machinegun is fed from the left side.

a.   Types. Two types of open emplacements for recoilless weapons are the pit type and the two two-man foxhole type.

b.   Blast effects. Due to the backblast effects of the recoilless weapon, it should not be fired from a confined space such as a fully covered emplacement. Because the backblast will reveal the firing position, alternate firing positions with the connecting trenches should be constructed if there is sufficient time.

a.   General. The emplacement illustrate in , figure 1-22 is circular in shape. The emplacement is excavated to the dimensions shown with the sides of the emplacement sloping inward toward the bottom. The floor slopes to the drainage sump located under the open gap in the parapet. An ammunition ready rack or niche, located so that it is convenient for the gunner, is built into the side of the emplacement. The bottom of the ammunition rack is elevated from the floor of the emplacement. Another ready rack may be constructed in one side of the trench leading to the position. The initial emplacement is revetted using sandbags and the improved emplacement is revetted using corrugated metal. Before constructing the parapet, the mortar is laid for direction of fire by the use of an aiming circle or alternate means. The parapet should be not more than 50 cm (20 inches) high and a minimum of 1 meter (3 feet) wide. An exit trench may be constructed leading to personnel shelters and to other mortar positions. Construction of the parapet should be coordinated with the infantry commander.

b.   The 81-mm mortar. A pit type emplacement for the 81-mm mortar is shown in , figure 1-22.

c.   Emplacement for 4.2-inch mortar. The 4.2-inch mortar emplacement is identical to the one parapet, care being taken to pile it so as to permit all-round fire of the weapon. Although 360° fire is possible from described above for the 81-mm mortar except for dimension changes shown in , figure 1-22.

a.   Purpose. Emplacements for artillery weapons must provide maximum flexibility in the delivery of fire and protect the weapon and its crew against the effects of conventional and nuclear weapons.

b.   Emplacement for 105- and 155-mm howitzer. Artillery weapons emplacements are constructed so as to allow for continuous improvement in order to provide additional protection and comfort in the event of prolonged occupation. These emplacements are developed in stages as described in (1) through (4) below.

c.   Accessory structures.

a.   Self-propelled artillery. Large caliber self-propelled weapons have a limited traverse without turning the vehicle. For this reason it is seldom practical to construct emplacements for this type of weapon. When positions for self-propelled weapons are prepared, a sloped ramp is built to facilitate the vehicle's entry into and withdrawal from the gunpit. In extremely cold weather, gravel, saplings, or similar covering may be necessary for the floor of the pit so that the tracks of the vehicles will not freeze to the ground. The rear of the pit and the sloped ramp should be widened sufficiently to permit driving the vehicle in at an angle in order to compensate for the limited traverse of the weapon.

b.   Tanks. A tank is emplaced or protected in the same manner as any other vehicle. Natural defilades such as road cuts or ditches are used where available. In open areas, parapets are provided to protect the sides and front of the hull of the vehicle, and the rear is left open. The simplest form of a dug-in position of this type is shown in figure 1-28. Whenever possible, such positions are constructed and occupied during darkness, with all camouflage being completed before dawn. The emplacement normally includes foxhole protection for relief personnel, preferably connected with the emplacement by a short trench. A dug-in emplacement of this type should have the following:

a.   The siting of artillery positions in areas where the ground is soft requires the construction of pads to preclude differential settlement and thus the relaying of the weapon after each round is fired. Wooden pads can be built using laminated construction of radial sleepers (fig. 1-29) and other construction techniques. The wooden pad distributes the load over a large area with no significant settlement and is flexible and strong enough to withstand the turning and movement of self-propelled weapons. The trail logs are anchored just outside the pad for towed weapons. For self-propelled weapons, the recoil spades can be set in compacted material or in a layer of crushed rock just off the pad. Figure 1-30 shows position with pad for the 8-inch or 175-mm gun and figure 1-31 shows another pad for these guns which has non-radial sleepers and laminated flooring. Figure 1-32 shows a concrete gun pad for these weapons. Figure 1-33 shows light and medium artillery battery layouts. Revetments and shelters can be constructed as described in paragraph 1-21.

b.   Various synthetic materials, such as fiberglass mats (also used as helicopter landing pads), may be used as gun pads depending on the characteristics of the weapons.

a.   Phase 1.   Phase I, combat assault and initial clearing, consists of securing the firebase site and clearing an area large enough to accommodate CH-47 and CH-54 helicopters. The time required to complete this phase depends on the terrain at the firebase site. If the site is free of trees and undergrowth, or if these obstacles have been removed by artillery and tactical air fire preparation, combat engineers can move immediately to Phase II after the initial combat assault on the site. If the site is covered with foliage and trees, the security force and combat engineers may be required to rappel into the site from hovering helicopters. Depending on the density of the foliage on the site, completion of the initial clearing phase by combat engineers with demolitions and chain saws may take up to three hours to accomplish.

b.   Phase II.   Phase II, immediate tactical construction, commences as soon as the cleared area can accommodate either medium or heavy lift helicopters. Two light airmobile dozers are lifted to the site and are immediately employed clearing brush and stumps to expand the perimeter and to clear and level howitzer positions. Meanwhile, the combat engineers continue to expand the perimeter with chain saws, demolitions, and bangalore torpedoes. If sufficient area is available, a heavy airmobile dozer usually is committed to clearing a logistic storage area and slingout pad, then to expanding the perimeter and fields of fire. The backhoes are committed to excavating positions for the infantry TOC, artillery FDC and, as soon as the perimeter trace is established, perimeter fighting bunkers. The immediate tactical construction phase is characterized by the coordinated effort of infantry, artillery, and engineer forces to produce a tenable tactical position by nightfall on the first day. It is a time of intense helicopter traffic introducing personnel, ammunition, barrier and bunker materials, rations, fuel, water, and artillery pieces onto the site. Aircraft traffic and logistics input must be rigidly controlled to preclude nonessential supplies and aircraft from hampering engineer effort. Therefore, a coordinated site plan and list of priorities for transportation and construction must be prepared and constantly updated. Priorities and the site plan are established by the tactical commander in coordination with the project engineer. As soon as a perimeter trace is established and the site is capable of accepting the logistics and artillery lifts, maximum effort is directed toward the defenses of the firebase. Combat engineers and the heavy dozer continue to push back the undergrowth to permit adequate fields of fire. The two light airmobile dozers may be committed to construction of a 1.2 meter (4 ft) berm around the perimeter to protect against direct fire. Infantry troops are committed to constructing perimeter fighting bunkers at sites previously excavated by the backhoes and, assisted by combat engineers, begin erection of the first band of tactical wire, usually triple standard concertina. Artillery troops not committed immediately to fire missions prepare ammunition storage bunkers and parapet around each howitzer.

c.   Phase III.   Phase III, final defensive structures, is initiated as construction forces complete the immediate defensive structures. Combat engineers who are not placing the tactical wire or clearing fields of fire commence construction of the infantry TOC and artillery FDC. Infantry and artillery troops are committed to the second band of tactical wire and to erecting personnel sleeping positions with overhead cover. Culvert half sections lend themselves to rapid construction of these positions. Phase III is usually a continuous process, involving constant Improvement and maintenance; however, the majority of protective structures, including sandbag protection of the TOC and personnel bunkers, usually are completed by the end of the fourth day. The controlling parameter in construction of a firebase is time; since the firebase is the first phase of the occupation of a hostile area, the battalion command center and the artillery pieces must be operational as soon as possible and protection against direct and indirect fire requires immediate attention. Several techniques have been developed to increase the efficiency and speed with which construction can progress. Among these are precut TOC structures and the use of culvert as molds for protective bunkers. However, the most effective technique yet adopted is a closely coordinated and controlled plan, outlining the location, priority, and construction force for each phase of the mission.

a.   The primary purpose of the base is to provide positions for artillery. Thus, physical layout of the fire support base (FSB) will give best possible fields of fire to guns.

b.   The base TOC will be located as near FDC as the base terrain allows. The TOC should be fairly centrally located and in a position to control base defense by visual means, if necessary.

c.   The helicopter logistical pad should be within the base perimeter but be situated so that incoming and outgoing aircraft do not fly through the primary or most likely sector of fire of the artillery.

d.   An admin/VIP helipad large enough for two UH-1 type aircraft should be located in the vicinity of the TOC.

e.   If a helicopter rearming/refueling facility is located on the FSB, it should not be so near to either the gun positions or artillery ammunition storage pits that a fire or explosion of one will damage the others.

f.   A landing zone for troop lift operations may be located outside the FSB but in the immediate vicinity of the perimeter positions.

g.   Typical battery layouts are shown in figure 1-33.

a.   Platforms which allow the howitzers or guns to fire in all directions and be capable of supporting repeated firing shock in any type of soil condition.

b.   Shelters capable of providing adequate protection for the firing crew.

c.   Separate shelters large enough to contain an artillery section basic load of projectiles, fuzes, and propelling charges.

d.   A wall or parapet around each howitzer or gun to protect the crew from fragments and small arms. The wall should be low enough to allow direct howitzer fire.

e.   FDC/TOC shelters large enough to contain the personnel and equipment necessary for the operation of the fire direction center and tactical operations center.

a.   Protection. Shelters are constructed primarily to protect soldiers, equipment, and supplies from enemy action and the weather. Shelters differ from emplacements because there are usually no provisions for firing weapons from them. However, they are usually constructed near or supplement the fighting positions. When natural shelters such as caves, mines, woods, or tunnels are available, they are used instead of constructing artificial shelters. Caves and tunnels must be carefully inspected by competent persons to determine their suitability and safety. The best shelter is usually the one that will provide the most protection with the least amount of effort. Actually, combat troops that have prepared defensive positions have some shelter in their foxholes or weapon emplacements. Shelters are frequently prepared by troops in support of front unit. Troops making a temporary halt in inclement weather when moving into positions prepare shelters as do units in bivouacs, assembly areas, rest areas, and static positions.

b.   Surface shelter. The best observation is from this type of shelter and it is easier to enter or leave than an underground shelter. It also requires the least amount of labor to construct, but it is hard to conceal and requires a large amount of cover and revetting material. It provides the least amount of protection from nuclear weapons of the types of shelters discussed in this manual. Surface shelters are seldom used for personnel in forward combat positions unless they can be concealed in woods, on reverse slopes, or among buildings. It may be necessary to use surface shelters when the water level is close to the surface of the ground or when the surface is so hard that digging an underground shelter is impractical.

c.   Underground shelters. Shelters of this type generally provide good protection against radiation because the surrounding earth and overhead cover are effective shields against nuclear radiation.

d.   Cut-and cover shelters. These shelters are dug into the ground and backfilled on top with as thick a layer as possible of rocks, logs, sod, and excavated soil. These and cave shelters provide excellent protection from weather and enemy action.

e.   Siting. Whenever possible, shelters should be sited on reverse slopes, in woods, or in some form of natural defilade as ravines, valleys, and other hollows or depressions in the terrain. They should not be in the path of natural drainage lines. All shelters must be camouflaged or concealed.

a.   Principles. Hasty shelters are constructed with a minimum expenditure of time and labor using available materials. They are ordinarily built above ground or dug in deep snow. Shelters that are completely above ground offer protection against the weather and supplement or replace shelter tents which do not provide room for movement. Hasty shelters are useful in the winter when the ground is frozen, in mountainous country where the ground is too hard for deep digging, in deep snow, and in swampy or marshy ground.

b.   Sites for winter shelters. Shelter sites that are near wooded areas are the most desirable in winter because these areas are warmer than open fields. They conceal the glow of fires and provide fuel for cooking and heating. In heavy snow tree branches extending to the ground offer some shelter to small units.

c.   Materials.

a.   Lean-to shelters. This shelter (fig. 1-34) is made of the same material as the wigwam (natural saplings woven together and brush). The saplings are placed against a rock wall, a steep hillside, a deadfall, or some other existing vertical surface, on the leeward side. The ends may be closed with shelter halves or evergreen branches.

b.   Two-man mountain shelter. This shelter (fig. 1-35) is useful, particularly in winter or in inclement weather when there is frequent rain or snow. It is basically a hole 2.1 meters (7 feet) long, 1 meter (40 inches) wide and 1 meter (40 inches) deep. This hole is covered with 6 to 8 inch diameter logs; then evergreen branches, a shelter half, and local material such as topsoil, leaves, snow, and twigs are added. The floor may be covered with evergreen twigs, a shelter half, or other expedient material. Entrances are provided at both ends if desired. A fire pit may be dug at one end for a small fire or stove. A low parapet is built around the emplacement to provide more height for the occupants. This shelter is very similar to an enlarged, roofed, prone shelter (figure 1-5).

a.   Drainage. Drainage is an important problem particularly in cut-and-cover and cave shelters. After the shelter is dug, drainage work usually includes keeping the surface and rain water away from the entrance, preventing the water from seeping into the interior by ditching, and removal of water that has collected inside the shelter. The floors of shelters must have a slope of at least 1 percent toward a sump (fig. 1-36) near the entrance, while the entrance should be sloped more steeply toward a ditch or sump outside the shelter (fig. 1-37).

b.   Ventilation. It is particularly important to ventilate cave shelters, especially if it is necessary to close the entrances during an attack. In surface and cut-and-cover shelters, enough fresh air usually is obtained by keeping entrances open. Vertical shafts bored within cave shelters are desirable if not absolutely essential. A stovepipe through a shaft assists the circulation of air. Shelters that are not provided with good ventilation should be used only by personnel who are to remain inactive while they are inside. Since an inactive man requires about .03 cubic meters (1 cu ft) of air per minute, unventilated shelters are limited in capacity. Initial airspace requirements for shelters for not over 12 men are 10 cubic metes (350 cu ft) per man.

c.   Entrance covering. If gasproof curtains are not available, improvised curtains made of blankets hung on light, sloping frames may be used. They should be nailed securely to the sides and top entrance timbers. Curtains for cave shelters should be placed in horizontal entrances or horizontal approaches to inclines. Windows should be covered with single curtains. All crevices should be caulked with clay, old cloths or sandbags. Flooring or steps in front of gas curtains should be kept clear of mud and refuse. Small, baffled entrances and/or right angle turns will reduce the effects of nuclear blasts and will keep debris from being blown in. Baffle walls may be constructed of sods or sandbags. Materials which may be injurious to the occupants should be avoided.

d.   Sanitary conveniences. Sanitary con-veniences should be provided in all but air-raid emergency shelters and surface-type shelters, where latrines are available. Disposal is by burial or chemical treatment. When waterborne sewage facilities are available, disposal can be into septic tanks or sanitary sewers.

e.   Light security. Blackout curtains should be installed in the entrance to all shelters to prevent light leakage. To be most effective, blackout curtains are hung in pairs so that one shields the other. Blankets, shelter-halves, or similar material may be used for this purpose.

f.   Emergency exits. Emergency exits in larger shelters are desirable in case the main exit is blocked. If possible, the emergency exit should be more blast-resistant than the main entrance. This can be done by making it just large enough to crawl through. Corrugated pipe sections or 55-gallon drums with the ends removed are useful in making this type of exit. A simple emergency exit which is blast resistant can be constructed by sloping a section of corrugated pipe from the shelter up to the surface, bracing a cover against the inside, and filling the section of pipe with gravel. When the inside cover is removed, the gravel will fall into the shelter, and the occupants can crawl through the exit without digging.

g.   Interior marking of shelter. The entrances or interior walls of shelters whose personnel capacity makes it desirable may be marked by reflective tape or paint to facilitate the entry of troops under darkened conditions. There should be no sacrifice of camouflage discipline.

a.   Size. Shelters 2 to 3 meters (6.5 to 10 ft) wide by 4.2 meters (14 ft) long are suitable for normal use.

b.   Timbers. All timbers should be the same size, if possible, approximately 15 to 20 cm (6 to 8 in.) in diameter depending on the width of the shelter (table 1-4). The uprights should be approximately 60 cm (2 ft) apart except at the entrance where they may have to be spaced farther apart. The roof supports should be spaced the same as the uprights. Holes should be drilled for driftpins at all joints.

c.   Bracing. Boards 2.5 by 10 cm (1 in. by 4 in.) in size for the diagonal bracing are nailed to caps, sill, and uprights.

d.   Walls. The log shelters should be covered with board or saplings and backfilled with approximately 60 cm (2 ft) of earth, or hollow wall may be constructed around the buildings and filled with dirt.

e.   Cover. A roof of planks, sheet metal, or other material is then laid over the roof supports and perpendicular to them to hold a minimum of 46 cm (18 in.) of earth cover which is effective against fragmentation (shrapnel) effects of mortars, artillery, and rockets.

a.   Siting. The shelter should be sited on a reverse slope for cut-and-cover construction.

b.   Excavation. Assuming that each bent or side unit (fig. 1-39 and table 1-5) is sheathed before installation, the excavated area should be 2.1 meters (7 ft) wide and 3 meters (10 ft) long for one section. The additional length of the excavated area will provide working space to install sheathing on the rear unit. The area for the shelter should be excavated to a depth of 3.6 meters (12 ft) to allow for a heavy overhead cover laminated roof and 3.2 meters (10 ft 6 in.) for heavy overhead cover stringer roof.

c.   Assembly. The two bents or side units may be assembled and sheathed before they are placed in the excavated area. In this manner driftpins are installed in the sill, caps and posts before units are placed in the excavated area. Bracing on the side units as well as the bracing and spreaders on the front and rear units are toenailed.

d.   Organization of work crews. An engineer squad, or a squad other than engineer under engineer supervision, can be used economically at the worksite to excavate the shelter area, assemble the roofing and cover materials, and construct the overhead cover. Under favorable conditions a trained engineer squad can excavate the area required for the shelter and install the shelter and overhead cover in 18 to 20 hours. However, if a backhoe or bucket loader is available for the excavation, the time can be reduced to approximately 6 hours.

a.   Definition. A standoff is a steel or wood curtain or chain link fence erected approximate 3 meters (10 feet) in front of a protective structure to detonate shells and thereby reduce their subsequent penetrating effect. Its use is optional but desirable as additional protection of those protective structures most likely to sustain enemy fire.

b.   Construction "condition". A construction "condition" (fig. 1-40 and table 3-3) refers to protective structure with or without a standoff. Condition I means the protective structure has no standoff, condition II - the structure has a steel standoff, and condition III - the structure has a wood standoff (fig. 1-41 and 1-42). A chain link fence standoff is shown in figure 1-43. Table 1-6 shows comparison of relative thicknesses of protective materials needed to withstand penetration of various types of ammunition - with and without standoffs.

a.   Cut-and-cover shelters. The log shelter shown in figure 1-38 is suited to cut-and-cover construction or surface construction. The best location for cut-and-cover shelters is on the reverse slope of a hill, mountain, ridge, or steep bank as shown in figure 1-44. The shelter shown provides 1.8 to 2.1 meters (6 to 7 feet) headroom. The shelter frame is built in the excavation; the spoil is backfilled around and over the frame to ground level, or somewhat above, and camouflaged. The protection offered depends on the type of construction (size of timbers) and the thickness of the overhead cover. As in the case of a surface shelter of similar construction, approximately 45 centimeters (18 inches) of earth cover can be supported.

b.   Cave shelters. Caves are dug in deliberate defensive positions, usually by tunneling into hillsides, cliffs, cut, or ridges or excavating into flat ground. Because of the undisturbed overhead cover, a cave is the least conspicuous of all types of shelters if the entrance is covered. One of the best locations for a supply cave entrance is shown in figure 1-45. The disadvantages of cave shelters include limited-observation, congested living conditions, small exits, and difficult drainage and ventilation. Their construction is difficult and time consuming. Exits may be blocked or shoring crushed by a direct hit from a conventional weapon or ground shock from a nuclear explosion.

a.   Observation posts. These are located on terrain features offering as good a view as possible of enemy-held areas (fig. 1-46). The ideal observation post has at least one covered route of approach and cover as well as concealment, while offering an unobstructed view of enemy-held ground.

b.   Command posts. Small unit command posts may be located in woods, ravines, in the basements of buildings, or former enemy fortifications. When none of these are available, surface or cut-and-cover shelters previously described may be modified for this purpose.

c.   Medical air stations. Cut-and-cover shelters are especially adaptable as aid stations since they are easily cleaned and ventilated. Suitable sites may be found in pits, quarries, under banks, or in small buildings or ruins.

d.   Ammunition shelters. Ammunition shelters should be located and constructed so that they protect ammunition against the weather and enemy fire. They should be well concealed, and large enough to hold the desired quantity of ammunition close to the firing position. Figure 1-47 shows an ammunition shelter which may be constructed in an emplacement parapet. If it is necessary to construct ammunition shelters above ground, particularly where the water level is close to the surface, a log crib built up with dirt is suitable.

a.   Laminated roof construction. In this design either five 5 centimeters (2 inch) or seven 2.5 centimeters (1 inch) layers of lumber are used for laminated roof as shown in , figure 1-48.

b.   Stringer reef construction. Figure , 1-48 illustrates stringer roof construction of heavy overhead cover. The construction is similar to laminated roof construction with the addition of —

c.   Overhead cover for fight b. Figure 1-49 shows the details for the construction of a fighting bunker with heavy overhead cover. The material requirements for the construction of this bunker are found in table 1-7.

d.   Heavy overhead cover protection. Heavy overhead cover protects against the following Soviet weapons:

152-mm gun-howitzer
122-mm howitzer
85-mm gun
120-mm mortar
82-mm mortar
140-mm rocket
122-mm rocket

a.   Overhead cover is normally supported on the roof of the structure and the resultant load is transmitted through the cape and posts to the foundation on which the structure rests. It may be necessary, in some instances, to support the roof directly on the earth outside a revetted position. When this must be done, the roof timber should not bear directly on the earth outside the excavation. The added load may use the wall to buckle or cave in. Instead, the roof structure is carried on timber sills or foundation logs bedded uniformly in the surface at a safe distance from the cut. This distance should be at least one-fourth the depth of the cut and in no case less than 30 cm (12 in.) to the nearest edge of the sill. Round logs used for this purpose are embedded to at least half their diameter to provide maximum bearing area of log to so. These principles are illustrated in figure 1-50.

b.   Laminated planks or stringers are used to support the roof cover.

c.   Sandbags are never used to support overhead cover.

a.   Shelters. Design considerations for the shelter design are set forth in the following guideline criteria:

b.   Fighting bunkers. Design considerations for the fighting bunker design are set forth in the following guideline criteria:

a.   Description. A basic unit of Waterways Experiment Station (WES) prefabricated concrete arch-type shelter is 3.6 meters (12-feet) wide and 1.2 meters (4-feet) long. A 3.6 meters (12-feet) long structure consists of three 1.2 meter (4-foot) long arch sections and two end wall sections, together with necessary hardware, waterproofing membrane, and earth cover.

b.   Design. This concrete arch shelter is designed to meet the essential and desired characteristics outlined in paragraph 1-45 and is subject to the following additional design factor assumptions:

c.   Transportation. Movement of the prefabricated arch sections and end walls to the emplacement site is accomplished by truck, trailer, or helicopter. Weight and dimensions are shown in table 1-10.

d.   Site preparation. Location and position of the shelter can be determined by the function of the shelter, the tactical conditions, the topography and other similar considerations which are determined by the field commander. The depth of excavation is determined by the elevation of the ground water table during the wet season. A bulldozer, scooploader, or crane-shovel with attachments is used to excavate a trench to receive the arch sections. A soft bedding or cushion layer of sand should be provided as a base upon which to set the arch sections to avoid structural stress concentrations, to absorb shock blast, effects, and to minimize unequal settlement between the arch sections, and walls, and entrance structures. Footings for each end wall consists of fourteen timbers 4 inches by 12 inches by 3 feet placed side by side and centered normal to the plane of the end wall. Typical trench excavation if shown in figure 1-53.

e.   Emplacement. The shelter sections can be emplaced by six men and one truck-mounted crane in 1 hour after site is prepared. The rough terrain crane which is available in the combat engineer battalion can be used effectively for final excavation, lifting the shelter sections into place and backfilling. The sections are firmly seated, alined, and secured with five wire rope tie assemblies. The four joints between the arch sections and end walls are covered with any durable, flexible, waterproof material such as salvaged T-17 membrane. Entrance structures at each end are fabricated from local or manufactured material including timber frame, concrete arch, corrugated metal pipe (CMP), cattle pass, or landing mat. Drainage structures are provided as required. The shelter is then backfilled with sod material. Sandy material, if available, will offer better protection than a clay type sod. The backfill placement should be carried on until a minimum depth of 4 feet and maximum depth of 8 feet insured; the depth of cover includes waterproof membrane, burster course, and camouflage.

a.   Description. The basic multiplate pipe arch shelter is a 3.6 meter by 3.6 meter (12-ft by 12-ft) prefabricated corrugated steel arch shelter consisting of one 3.6 meter (12-ft) multiplate pipe arch section and two precast reinforced concrete end walls, together with necessary hardware, waterproofing membrane, and earth cover.

b.   Design. The multiplate pipe arch shelters use commercial pipe arch which is available in a range of spans, rises, and areas and are tabulated in drainage products handbooks and manufacturer' catalogs. This multiplate arch is designed to meet the criteria outlined in paragraph 1-45 and is subject to the following design factor assumptions:

c.   Prefabrication of multiplate pipe arch section. The two slightly curved floor plates, the two curved (1-ft, 6-in. radius) corner plates, the two haunch plates, and the crown plate are lapped and secured with four 3/4-inch-diameter by 1 1/4-inch-long bolts per linear foot of seam. Bolts are staggered in two rows per seam with one bolt in each valley and each crest of the corrugation. Bolts should not be tightened until all bolts have been installed. Manufacture' catalogs, when available, should be consulted for detailed instructions on assembly technique.

d.   Transportation. Movement of the prefabricated arch sections and end walls to the emplacement site is accomplished by truck, trifler, or helicopter. Weights and dimensions are shown in table 1-11.

e.   Site preparation. Location and position of the shelter can be determined by the function of the shelter, the tactical conditions, the topography and other similar considerations which are determined by the field commander. The depth of excavation is determined by the elevation to which the ground water table can be expected to rise during the wet seasons. A bulldozer, scoop loader, CEV or crane-shovel with attachments is used to excavate a trench to receive the prefabricated pipe arch section and end walls. A soft bedding or cushion layer of sand should be provided as a base upon which to set the pipe arch section in order to avoid structural stress concentrations, absorb the shock of blast effects, provide drainage, and minimize unequal settlement between the arch section, end walls, and entrance structures. Timber footings under the end wall sections are required where the strength of subgrade is not capable of supporting the 1,000 psf load of end walls.

f.   Emplacement. The shelter sections can be emplaced by six men and one truck-mounted crane in 1 hour after site is prepared. The rough terrain crane which is available in the combat engineer battalion can be used effectively for emplacement, to include final excavation, lifting the shelter sections into place, positioning entrances, and back-filling. Wire rope slings are used to aid the placement of the structure. Entrance structures at each end are fabricated from local or manufactured material such as timber frame, concrete arch, CMP, cattle pass, or landing mat. After excavation has been completed to the proper elevation, a waterproof membrane is installed prior to placing the structure. All bolts should now be checked for tightness and the membrane material wrapped completely around the shelter. Backfill material, dry coarse sand if available, is now placed and compacted. Special attention should be given to the placement and compaction of the soil material under the upturn area of the floor section. Additional backfill material is placed and compacted in 15 cm (6-in.) lifts to an elevation of at least three-fourths o: the height of the structure. These procedures are necessary to provide symmetrical loading and to insure proper setting of the structure. To complete the emplacement, the backfill material is placed to a minimum height of 4 feet or up to a maximum height of 8 feet over the crown of the structure including burster layers and camouflage layers. Drainage is provided as required by the topography.

a.   Description. The concrete log bunker is a 4-man fighting bunker, 2-3 meters (7 ft, 6 in) square and 1.8 meters (6 ft) high. The bunker is constructed of 90 precast reinforced concrete logs 15 cm (6 in) wide by 20 cm (8 in) deep of various lengths (.6, .9, 1.2, 1.8, 2.4 and 3.0 meters (2, 3, 4, 6, 8, and 10 ft)) that weigh approximately 164 pounds per meter (50 lb per ft). The bottom of the bunker is set 102 cm (3 ft, 4 in) below the ground surface. The roof is made by placing 3 meter (10 ft)-long concrete logs side by side and pinning them together to make a 20 cm (8 in) -thick roof with 30 cm (1 ft) overhang on all sides. The bunker has a 20 by 45 cm (8- by 18-in.) firing port on each of the four sides; the bottom of each firing port is 1.2 meters (4 ft) above the floor level. The logs are joined together with steel pins, 1.9 cm (3/4 in.) in diameter, which are dropped through holes, 3.8 cm (1 1/2 in.) in diameter, alined at 30 cm (1 ft) intervals and cast in the logs. Normal entrance/exit is by means of .9 meter (3 ft) and 1.2 meter (4 ft) diameter corrugated metal pipe (CMP), and an emergency exit is provided by means of two removable logs at the rear face firing port.

b.   Design (fig 1-56). This concrete log bunker is designed to meet the characteristics outlined in paragraph 1-45.

c.   Forming, steel placement, and casting. The concrete logs are precast in a staging area and transported to the emplacement site. The forms are constructed in the field on a 3.6 by 4.8 meter (12- by 16-ft) casting bed which permits casting of numerous logs of various lengths at one time. The concrete is mixed, poured, vibrated, and cured in accordance with standard procedures. Two to five days' moist cure is required before the precast logs can be moved safely.

d.   Transportation. Movement of the precast concrete logs to the emplacement site is accomplished by truck, trailer, or helicopter.

e.   Site preparation. Location of the fighting bunker is determined by the tactical commander. The design depth o excavation is 2.54 meters (8 ft, 4 in.), including 102 cm (3 ft, 4 in.); below grade for bunker floor and 1.5 meters (5 ft) below bunker floor for the entrance; however, the elevation to which the ground water table can be expected to rise during the wet season may require a field modification of this design depth. The emergency exit, located above the normal ground level, allows siting of this bunker in locations where the normal entrance may be subject to temporary flooding. Excavation is accomplished by combat support earthmoving equipment or by hand digging.

f.   Emplacement. The concrete log fighting bunker can be assembled by six men in 1 hour after the site is prepared and the CMP entrance structure is in place. For poor soils, a footing will be required for this structure to prevent excessive settlement. Cushion, waterproofing, and burster layers, retained with sandbags, are placed on the roof to develop capability to withstand a direct hit from the equivalent of an 82-mm mortar round. Steel mesh grenade gratings are hinged over the firing ports. Standoff screening against AT rockets, fields of fire, communications, camouflage, firing shelves, and bunks should be provided as required. The modular design of the basic concrete logs permits a wide variety of original designs to suit specific requirements. This flexibility of design may be exploited by testing different arrangements using either full scale or model logs.

a.   Description. The concrete arch bunker is a four-man fighting bunker, semi-circular in plan, 3.6 meters (12 ft) wide at the rear by 2.25 meters (7 ft, 6 in.) deep at centerline of the arch width by 1.8 meters (6 ft.) inside height. The bunker consists of three precast reinforced concrete components: a 1.8 meter (6 ft.)-high arch section, a rectangular back wall section, and a semi-circular roof section. Each of the sections is 15 cm (6 in.) thick and reinforced with No. 4 1.25 cm (0.5-in. diameter) steel rebars. The arch section has a 1.8 meter (6-ft) interior radius plus a 45 cm (1 ft, 6 in.) horizontal extension. The roof section overhangs the arch section providing a 45 cm (18-in.)-wide shield. The back wall section and the roof section each have a 20 cm (8-in.)-thick by 45 cm (18-in.)-wide bulkhead beam. The arch section has four 20- by 45-cm (8- by 18-in.) firing ports, and the back wall has one 20- by 45-cm (8- by 18-in.) firing port and a 20- by 75-cm (8- by 30-in.) emergency exit which can be used for a quick exit or grenade throwing.

b.   Design. This concrete arch bunker is designed to meet the characteristics outlined in paragraph 1-45. Design is shown in figure 1-58.

c.   Forming, steel placement, and casting.

d.   Transportation. Movement of the three precast sections is accomplished by truck, trailer, or helicopter.

e.   Site preparation. Location of the concrete arch fighting bunker is determined by the tactical commander. The design depth of excavation 2.5 meters (5 ft 4 in.) including 1 meter (3 ft, 4 in.) below-grade for the bunker floor and 1.5 meters (5 ft) below the bunker floor for the entrance; however, the elevation to which the ground water table can be expected to rise during the wet season may require a field modification of this depth. The emergency exit, located at the firing port level, allows siting of the arch fighting bunker where the deep entrance may be subject to temporary flooding. Excavation is accomplished by combat support earthmoving equipment or by hand labor.

f.   Emplacement. The three sections of the arch fighting bunker can be employed by six men and one heavy crane in one hour after site is prepared and the CMP entrance structure is in place. The rough terrain cane which is available in the combat engineer battalion can be used effectively for emplacement especially for positioning of entrance and lifting and positioning bunker sections. The back wall is bolted to the 20- by 45-cm (8- by 18-in.) bulkhead beam at the rear of the roof section to secure the entire structure against displacement when under attack. Except in very good soil conditions, footings will be required under the modified arch section to prevent excessive settlement. Cushion, waterproof, burster layers, retained with sandbags, are placed on the roof to develop capability to withstand direct hit from the equivalent of an 82-mm Soviet mortar round. Steel mesh gratings are hinged over the firing ports. Standoff screening against antitank (AT) rockets, as well as fields of fire, communications, camouflage, firing shelves, and bunks should be provided as required.

a.   Description. This is a prefabricated plywood bunker (fig 1-59) suitable for a commandpost or fire-direction center, which can be moved (completely assembled except for the roof) from site to site as the tactical situation demands. Its sloping walls make for easier pulling from the ground by helicopter for relocation. The bunker can be erected and emplaced by means of handtools only.

b.   Construction. The bunker walls and floor may be prefabricated (fig 1-60) in rear areas and then be trucked or flown, assembled or disassembled, to the erection site. Fasteners are provided along the edges of each wall and the floor to allow the Individual members to be locked together into a complete unit. The walls of the bunker should extend below the floor section so that the floor can act as a support for the bottom edge of the walls. The longer side walls are abutted against the shorter end walls. Two large straps, completely around the structure, and placed during construction are used to attach bunker to helicopter lifting hook for bunker pullout and transport The underground site can be excavated by means of explosives and handtools (fig 1-61). The floor area of the excavation should be .6 meter (2 ft.) longer and .6 meter (2 ft.) wider than the area of the bunker floor to allow working space during construction. The roof is concentric to and larger than the floor section and may be fabricated in the rear area or at the erection site. The roof overlaps the walls to be supported on firm (unexcavated) ground - not on the bunker walls. Additional construction recommendations for the bunkers are as follows:

c.   Data. The bunker weighs approximately 1,600 pounds without the roof. It can be pulled from the ground by a lift of 10,000 pounds (CH-47 helicopter). The bunker should be no more than 1.95 meters (6 1/2 ft) high and the floor space should be under 9.3 square meters (100 sq ft). Excavation, erection, backfilling, and construction of roof and entrance can be completed in less than 10 hours.

a.   Protection. Some protection from enemy fire may be achieved for occupants in a building used as a shelter by strengthening the building, by shoring up ceilings, and bracing walls. Men inside buildings are reasonably well protected against thermal effects and radiation unless they are near doors or windows. The principal danger is from falling masonry and from fire in the building.

b.   Basic considerations.

c.   Use of weapons. In using a building as a firing position, there are several considerations.

a.   The wide distribution and cheapness of the material for constructing the fortifications and the presence the materials at the building site, thus eliminating their transportation.

b.   The extensive possibility of substituting snow, ice, and frozen ground during winter for the usual building materials.

c.   The relative speed of construction with snow, ice and frozen ground, especially the solidification speed of soils exposed to freezing.

d.   The simplicity and speed of repairing structures of snow, ice, and frozen ground if damaged.

e.   The great strength of structures made from frozen ground.

f.   The complete safety from fire.

a.   Suitability. Dry fresh fluffy snow is not suitable for expedient construction. Reworked snow, such as piles at road edge after clearing equipment passage, densifies and begins to harden within hours after disturbance even at very low temperatures. Artificial compacting wind compacting, and compacting after a brief thaw make snow even more suitable for expedient shelter and protective structures.

b.   Construction.

a.   Methods. Ice structures can be built in three ways:

b.   Construction.

a.   Suitability. Frozen ground is three to five times stronger than ice; its strength increases with lower temperature. It has much better resistance to impact and explosion than to steadily acting load, an especially valuable feature for fortification purposes.

b.   Methods. Construction using frozen ground is done by —

a.   Structures in subarctic regions. It is obvious that with the onset of warm weather, structures made of snow, ice, and frozen ground will disintegrate. A snow structure in early spring loses its camouflage. To extend its life, if needed, it should be covered with locally available material such as moss or forest litter. Depending upon the weather and layer thickness, the useful life of such a structure may be extended for more than a week.

b.   Structures in arctic regions. In regions of shallow seasonal thaw underlined by permafrost, structures from snow, ice, and especially permafrost may be made permanent. For this purpose, the structure should be covered with the same material as the local permafrost. Typically, in tundra regions, the permafrost is covered by a shallow layer of thick vegetation, the so-called tundra mat which protects the permafrost from melting during the summer. The careful removal of the tundra mat and the construction of the structure on bare ground, and then covering all exposed surfaces with tundra mat material, protects the structure against summer disintegration. Special measures should be taken to minimize disturbance of the area around the structure during construction. Any disturbance of the area around the structure should be repaired. Careful preparation of such an expedient protective structure makes it permanent if needed.

a.   To evaluate snow, ice, and frozen ground as materials for fortification, it is necessary to know the resistance of these materials to impact and explosion.

b.   A rifle bullet rapidly loses its penetrating power, depending on the density of the snow. Snow packed in layers deflects the bullet at each layer. Loose snow spread over a defensive position will help smother ricochets.

c.   Loose snow greatly reduces the explosive and fragmentation effects of shells. The depth, type of snow, and ammunition type are naturally the main consideration. The use of a delayed action fuse will generally cause the shell to penetrate the snow blanket and explode underneath, smothering and reducing the effect of the fragmentation. One meter (3.3 ft.) of snow will provide some protection against most light artillery fire. A superquick fuse setting will increase the effect of artillery fire, while airburst will cause still more damage to surface targets.

d.   Results of resistance tests of the impact of a bullet or explosion on samples of different frozen soils and icecrete at -4° C. are shown in table 1-12. On the basis of these test results the following general conclusions can be made:

a.   Snow-covered and icy slopes. A steep slope is an obstacle to troops and vehicles even under normal conditions. When covered by deep snow or ice, it becomes much harder to surmount. The bogging-down action and the loss of traction caused by deep snow frequently create obstacles out of slopes which might be overcome easily, otherwise.

b.   Windfalls. Occasionally, strong winds knock down many trees in a wooded area. These fallen trees are known as windfalls. They are very effective obstacles when covered with snow, especially to personnel wearing skis or snowshoes.

c.   Avalanches. An avalanche makes an excellent obstacle for blocking passes and roads. Since it occurs in mountainous country where there are few natural avenues of approach, an avalanche can have a far-reaching influence over combat operations. The problem with those avalanches which occur naturally is that, unless their timing and location are just right, they may be of help to the enemy. It is possible to predict in advance where an avalanche can and probably will occur. Then by the use of recoilless rifle or artillery fire, bombs, or explosives, it is possible to induce the avalanche to slide at the desired time. This type of avalanche is an artificial obstacle in the technical sense. Generally, it will be of more value than the natural type.

a.   Barbed wire. There are many types of artificial obstacles used under summer conditions which are appropriate for winter use. Barbed wire normally employed makes an effective obstacle in soft, shallow snow. Triple concertina is especially effective since it is easy to install in addition to being difficult to cross. As the snow becomes deeper and more compact, a point is reached where it is possible to cross the barbed wire on top of the snow. One type of barbed wire obstacle built to overcome this problem is known as the Lapland fence.

b.   Lapland fence. The Lapland fence uses a floating type of anchor point or one which is not sunk into the ground. Poles are used to form a tripod. The tripod is mounted on a triangular base of wood. Six strands of wire are strung along the enemy side of the fence, four strands along the friendly side, and four strands along the bas. As the snow becomes deeper, the tripods are raised out of the snow with poles or by other means to rest the obstacle on top of newly fallen snow. The base of the tripod and the base wires give enough bearing surface to prevent the fence from sinking into the snow.

c.   Knife, rests. Knife rests are portable barbed wire fences, usually constructed prior to the snowfall. The fences are constructed by tying two wood poles at their center, forming an X. A similar X is made out of two other poles and then the two X's are lashed at each end of a 3 meter (10 ft) to 3.5 meter (11.7 ft) pole. This forms a framework to which barbed wire is fastened on a four sides. The obstacles can be stored until needed and easily transported to the desired location.

d.   Concertina wire. Concertina wire is another quick way to improve on snow- covered obstacles. The concertina comes in 15 meter (50 ft.) sections which can be anchored quickly to the top of existing obstacles.

e.   Abatis. The abatis is similar to a windfall. Trees are felled at an angle of about 45° to the enemy's direction of approach. The trees should be left attached to the stump to retard removal. Along trails, roads, and slopes, abatis can cause much trouble for skiers and vehicles.

f.   Iced road grades. A useful obstacle can be made by pouring water on road grades. The ice that forms will seriously hamper vehicular traffic.

g.   Ice demolition. In creating water obstacles to the enemy during winter conditions it becomes expedient to place charges below the ice and under water. To place charges under water, make boreholes in the ice with axes, chisels, ice augers, or shaped charges, then place the main charge below the ice. A charge of 36.3 kg (80 lb) of M3 demolition blocks, through 1.37 meters (4 1/2 ft) of ice, produces a crater 12 meters (40 ft) in diameter. To create a minefield in ice, sink boreholes about 3 meters (10 ft) apart in staggered rows. Suspend charge below the ice by means of cords with sticks bridging the top of the holes. The charges should be set least 60 cm (2 ft) below the bottom of the (fig 1-68). The size of the charge depends on the thickness of ice. Activate the firing devices on two or three charges in each underwater minefield, one on each end and one in the middle. The rest of the charges will detonate sympathetically. Blowing a field like this creates an obstacle to enemy vehicles for approximately 24 hours at -24°F.

Lesson 1 Practice Exercise
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