en5485 Lesson 2

LESSON 2

ENGINEER OBSTACLES

OVERVIEW

LESSON DESCRIPTION:

This lesson addresses obstacles and their contributions to denial operations. It includes definitions, characteristics, and types of obstacles. It also covers doctrinal principles associated with producing, employing, and integrating obstacles in general.

LEARNING OBJECTIVE:

ACTION:	Identify the basic definitions, characteristics, types of obstacles, and the doctrinal principles associated with producing, employing, and integrating obstacles in general.
CONDITION:	Given the material contained in this lesson.
STANDARD:	Correctly answer all questions in the practice exercise at the end of this lesson.
REFERENCES:	The material contained in this lesson was derived from the following Field Manuals and material approved for instruction by the US Army Engineer School (USAES): FM 5-100 FM 5-102 FM 5-103 FM 5-71-100

INTRODUCTION

An obstacle is any obstruction that stops, delays, or restricts movement or maneuver. Obstacles include natural barriers, such as rivers or ravines, or man-made barriers such as minefields and tank ditches.

There are two groups of obstacles: existing and reinforcing. Existing obstacles are already present on the battlefield--not placed there through military effort. These are natural obstacles, such as lakes or mountains, and cultural obstacles such as towns or railroad embankments. Military forces emplace reinforcing obstacles (tactical, protective, and situational) on the battlefield. These obstacles strengthen the existing terrain to slow, stop, or canalize the enemy. Imagination, time, manpower, or logistical constraints are the only limits to reinforcing obstacles. Some examples of existing and reinforcing obstacles are shown in Table 2-1.

Table 2-1. Classification and examples of obstacles
Table 2-1. Classification and examples of obstacles

PART A: OBSTACLE CATEGORIES

2-1. Existing Obstacles.

a. Terrain and Terrain Analysis. The terrain, as it exists, is a significant asset to the commander who analyzes and uses it wisely. Terrain is not just a field where men fight—it is very much a part of the battle. Commanders who make the terrain work against their opponent strengthen their odds of winning.

Commanders must study the terrain on which their forces and the enemy will move and fight. The commander's course of action (COA) will largely depend on the terrain's characteristics and its intended use. The COA includes moving, maneuvering, and siting weapons to destroy the enemy. Existing obstacles affect all friendly and enemy ground movement.

A good terrain analysis in the areas of influence and interest should cover the elements of observation and fields of fire, cover and concealment, obstacles, key terrain, and avenues of approach (OCOKA) with respect to the effect on enemy and friendly forces. Some questions that should be answered are—

Where are the mobility corridors and AAs? Where will the enemy come from? Where can I go?

How large are the mobility corridors and AAs? What size enemy or friendly force will they support?

What is the trafficability of the AAs? How fast can a force travel and with what type vehicles?

Where is the key terrain? What terrain will provide a significant advantage to the one who controls it?

What are the fields of fire? With what weapons and at what ranges can I engage the enemy or can he engage me?

Where are the choke points or extensive obstacle areas? Where are possible locations to place reinforcing obstacles?

These questions are not all inclusive, but the answers will provide significant information on how to prepare the battlefield and distribute combat power. Some obvious existing obstacles are roads and bridges, built-up areas, soil, slopes, rivers and streams, visibility, climate, weather, and their effects.

Identifying and analyzing existing obstacle locations is a key element of terrain analysis. The most critical questions are how and where do we get information concerning terrain and existing obstacles A good source is a ground reconnaissance performed by the units that will fight the battle. This is not always possible due to a lack of resources or enemy control of the areas we need to examine. Corps and division terrain teams organic to the TA topographic battalion collect, analyze, and provide important topographic, hydrologic, and climatic data. Terrain analysis assesses elements of OCOKA. Input to the force engineer and the Assistant Chief of Staff, G3 (Operations and Plans) (G3) is especially important for obstacle planning. Engineer terrain analysts work with intelligence analysts to collect raw terrain information and convert it into processed intelligence. Topographic units provide a variety of products including cross-country movement maps, overprinted maps, and various scale tactical maps. Topographic support is invaluable in making a thorough terrain analysis.

Analysis of the terrain and existing obstacles should focus on tank mobility. Enemy combined arms forces design their tactics around tank mobility. The tank is the primary vehicle we want to restrict, delay, stop, or kill. This AT orientation of terrain analysis and obstacle development narrows our focus and makes the task simple. Terrain analysis aids a commander in identifying existing obstacles that will restrict canalize, delay, or stop tanks.

b. Systematic Terrain Analysis. This analysis uses all assets available to reveal the terrain's existing obstacle value. Consider drainage features, slope and relief, vegetation, cultural features, and climate. Then, determine each feature's obstacle value for trafficability. The combined effect becomes the terrain's obstacle value. Use the existing terrain to support the maneuver scheme and to reduce the amount of reinforcing obstacle effort required. Also, identify how terrain will impede our own mobility. Friendly forces can then assign assets (such as the armored vehicle-launched bridge (AVLB)) to overcome restrictions.

(1) Drainage features. Drainage features include rivers, streams, and canals. Lakes, ponds, marshes, swamps, and bogs are surface-water features. These are obstacles that threaten the safety of soldiers and vehicle operations whenever the water is deep or turbulent. Drainage features are also obstacles when swamps, marshes, and bogs make soil conditions impossible for cross-country movement. Dry stream channels provide avenues for movement during periods of little or no water flow. There may also be quicksand or other soft places present where vehicles can get stuck.

(a) Large rivers. Large, unfordable rivers are formidable obstacles. Forces must cross them by tactical bridging, swimming, ferrying, or special deep-water fording. Determine their ease of crossing by examining their width, depth, velocity, and turbulence. Also, consider the bank and bottom conditions, existing bridges, and rapid tactical bridging capability (see Figure 2-1).

(b) Small rivers, streams, and canals. Minor fordable rivers, streams, and canals are much more numerous than major rivers, so do not overlook their tactical value as obstacles. These features vary in effectiveness as obstacles. Carefully plan their integration into the obstacle system. Watercourses are frequently lengthy obstacles in terrain that may otherwise be excellent for movement.

Drainage also influences the orientation of the road net and the direction of movement in an area. Destroying a few selected bridges can force cross-country movement or long detours.

Minor rivers and streams can become major obstacles during floods. They can cause conditions that extend the obstacle effect for a considerable period by damaging temporary and expedient bridges and by deepening the original channel of the river or stream, thus making access or egress difficult.

(c) Weather effects. Streams are normally small and slow during periods of low precipitation. However, they become large and rapid during periods of high precipitation. The relationship is not always this simple. Melting snow, for example, may cause high water downstream, even in regions where rainfall is low. Continuous below-freezing weather can reduce stream flow even though precipitation may be high.

In winter, ice may be strong enough to support vehicles; then, instead of being obstacles, water bodies become the preferred avenues for movement. Lightly loaded 2 1/2-ton trucks can move on ice 0.3 meter (10 inches) thick. Movement on ice is risky because of weaknesses caused by water flowing from springs or other swiftly-moving water sources.

(d) Fording. Stream fordability determines whether a force will cross it without the means of bridging or ferrying. Fordability depends on the stream's characteristics, including the following:

Width of channel.

Depth and velocity of water.

Nature of bottom.

Bank conditions (height, slope, and strength).

Figure 2-1. Critical drainage factors

These characteristics may vary, so fording even the smallest stream requires selecting a site where favorable conditions exist. A stream is a minor hindrance when a ford site is available and needs little or no improvement; it is a major hindrance if a suitable ford site is lacking or if fording requires considerable preparation of approaches, reinforcement of bottoms, or the use of special equipment on vehicles. A tank can bridge stream channels less than 3 meters wide; however, wheeled vehicles do not have this capability.

Once a stream exceeds the self-bridging capability of tacked vehicles, cross only by bridging ferrying, or fording. Although the width of streams is significant to bridging, it is insignificant to ferrying and fording. However, the wider the stream, the more hazard involved. For fording, the maximum permissible depth of water for most tanks is 0.9 to 1.5 meters (3 to 5 feet). Trucks can ford up to 0.9 meter (3 feet). Vehicles equipped with deep-water fording devices can cross water bodies as deep as 5 to 6 meters (17 to 20 feet). Stream velocities should be less than 1.5 meters (5 feet) per second for reasonably safe fording. Often, the first few vehicles negotiate a ford with minor difficulty, but remaining vehicles cannot cross because bottom conditions or approaches deteriorate with use.

The bottoms of streams must be firm enough to support vehicles. Bottoms made up of fine-grained material can prevent fording even though the water is only a few inches deep. Sandy, gravelly, or rocky bottoms make suitable bottoms for crossing; however, sandy bottoms may give way under the weight of vehicles. Boulders on the bottom may also prevent vehicular movement.

The banks are also important. Hard, vertical banks will be obstacles to tanks if the bank height exceeds 1.5 meters (4 feet) and to trucks if the bank height exceeds 0.3 meter (1 foot). Vehicles can tolerate more height if they can get adequate traction or use a winch. The type of material composing the banks may be significant. Banks made of fine-grained soils may fail under repeated traffic. Sandy and gravelly materials usually provide adequate strength and durability.

Adequate information (river studies and special maps) is commonly available for large streams but is not always available for small streams. Ground reconnaissance is always the preferred method of obtaining this information. If ground reconnaissance is not possible, then use topographic and geographic maps, reports, and aerial photographs. Occasionally, publications on geology, agriculture, soils, and forestry will provide good information.

(e) Lakes, ponds, swamps, marshes, and bogs. Large lakes make excellent obstacles. They are usually unfordable and do not allow bridging, so look for ways to bypass them. Smaller lakes and ponds by themselves are not difficult to bypass; however, when connected by streams, they become part of an obstacle system. When lakes are frozen, they may lose their value as obstacles. Swamps, marshes, and bogs severely restrict mobility. They force the canalization of vehicular movement onto causeways, increasing vulnerability to attack by air, artillery, or direct-fire weapons. Historically, attacking armies avoid swamps. Swamps and marshes over one meter deep may be more effective obstacles than rivers since causeways are usually more difficult to construct than bridges.

(f) Soils. Soil trafficability, especially when considered with climatic conditions, is a very important factor in evaluating cross-country movement. Gathering the needed information, however, is difficult and time-consuming. Properly assessing the trafficability strength of soil is also complicated. Engineer soils-analysis personnel and qualified photo interpreters are capable of estimating soil strengths. Higher headquarters requires soil strengths for planning purposes. Soil moisture significantly affects the load-bearing capacity of fine-grained soils such as clay, loam, and silt. This is due to the effects of drainage on the water table. Artificially produced high-water tables have made obstacles of meadows or paddy fields, which cover large areas. Further, the long-term use of manure for fertilizer adds organic material that reduces the soil's trafficability when wet. The combination of soft or slippery soils and even slight slopes, will stop many vehicles. Tanks have extremely low ground pressures (8 to 12 pounds per square inch (psi), 0.56 to 0.85 kilograms per square centimeter (kg/cm2)). They have less difficulty with most soils than other vehicles.

(g) Snow. Snow creates a special cross-country movement problem related to soils. Though seldom a serious obstacle to tracked vehicles, snow in the spring or fall may cause oversaturated, untrafficable ground. It is more of a hindrance and hazard to wheeled vehicles, as most will become immobilized when the snow depth reaches one-third of the tire's diameter. Snow reduces slope-climbing ability, maximum payload capacity, maneuverability, and speed of all vehicle operations.

(2) Slope. Slope is the inclined surface of a hill, mountain, or ridge. It is the inclination of major surface-relief features (hills and mountains). It also can be found on minor relief features such as ditches, small gullies, mounds, low escarpments, small pinnacles, and sinkholes. These do not always appear on topographic maps. Although some of the minor relief features might be roughness factors rather than slope, include them in the slope factor. Their obstacle value is due to the steepness of their slopes, banks, or faces. Short, vertical slopes higher than 0.3 meter (1 foot) will slow wheeled vehicles; those higher than 1.5 meters (4 feet) will stop tanks.

In mountainous areas, steep slopes commonly make cross-country vehicular movement either difficult or impossible. Existing terrain might canalize movement.

Slope is the difference in elevation measured in meters per 100 meters of horizontal distance. It is shown in terms of percentage. Most military vehicles can climb slopes of 60 percent (about 30/35 degrees) under favorable conditions. However, this limit is too much to negotiate in military operations. In assessing terrain for cross-country movement, use 45 percent (about 27 degrees) as the reasonable upper limit for tanks, and use 30 percent (about 17 degrees) for trucks. Wet weather, trees, unfavorable soil conditions, snow, boulders, and reinforcing obstacles may make gentle slopes impassable.

For the most reliable information on slopes (particularly short, steep ones), conduct a ground reconnaissance. Topographic maps are useful, but they do not show all features (small gullies, dense underbrush, and so forth). Terrain teams are the best overall source of up-to-date information to determine slope and other terrain information if a ground reconnaissance is not possible.

(3) Vegetation. Vegetation includes not only naturally-occurring vegetation but also cultivated forests and crops. Forest vegetation is the primary concern in cross-country movement. Trees are the principal obstacles to movement. Although high grass and brush can obstruct vision, they are of relatively little significance in most cases. Nearly all forests, however, slow movement.

The problem is to determine whether a particular forest will slow movement slightly, drastically, or stop it altogether. Temperate zone forests canalize movement since roads, trails, and firebreaks through them provide the only means for rapid movement. Tree size and density, soil condition, slope, and depth enhance the forest's obstacle value. Forests with trees 20 to 25 centimeters (8 to 10 inches) in diameter are tank obstacles. Trees 5 centimeters (2 inches) thick will stop most wheeled vehicles. Overturning trees within forests can also create complications. For example, by pushing over several trees, some will interlock with other trees to form a better obstacle to movement. The protruding root system and trunks of overturned trees are obstacles to vehicles. The critical average distance between trees, in forests where trees are too big for tanks to push over, is about 3 to 5 meters (10 to 16.5 feet). This also depends on whether the trees are evenly or unevenly planted. Although this distance may be wide enough for vehicles to pass through, in most cases there is no turning space.

Reconnaissance is especially important as a source of forest-vegetation information. You can determine the size of trees and the distances between them. This cannot be determined from aerial photography. Tree blowdown during nuclear attack will present significant mobility problems. Affected forested areas will be impassable to tracked and wheeled vehicles.

(4) Cultural features. Cultural features are man-made features such as stone walls, hedgerows, dikes, canals, drainage ditches, embankments, cuts, fills, and built-up areas. They may also include damaged or abandoned vehicles. Consider some of these features when evaluating the slope factor and streams. Cross-country movement studies frequently do not evaluate some cultural features such as built-up areas. Treat cultural features as separate factors to ensure that you do not overlook them in assessing terrain for cross-country movement.

The cultural feature's obstacle value depends on its size or extent, location, and construction. Large cities and towns that have many masonry buildings located astride principal communications routes can become obstacles of considerable importance. When reduced to rubble, they restrict enemy movement. Even if a force clears gaps through the rubble and debris, their movement is still canalized.

(a) Road and railroad nets. Other extremely important cultural features are the road and railroad nets. These will influence an attacker's choice of approaches because--

The expected rate of advance will force the attacker (except the lead elements of his main body) to move on roads, unless combat or imminent combat forces him to deploy into tactical formations.

The road net is critical to the movement of the attacker's following formations.

The attacker must have a well-developed road or railroad net for his logistics support.

Every break in the road or railroad net creates an obstacle to an attacker's rapid tactical movement. This will affect the movement of his following formations and logistics. If the break is in his division rear area or farther back, its effect is interdiction. Corps and division obstacle plans, as well as denial plans, must consider this effect. A highly developed road or railroad net with its many cuts, fills, and embankments creates possible obstacles to crossing movement. These are comparable in extent to the drainage network.

(b) Minor cultural features. Minor cultural features can also act as deterrents or obstacles to movement. A stone wall or hedgerow is a serious obstacle unless the sheer weight of a vehicle can push through it. The height and thickness of such walls or hedgerows, the height of embankments, and their slope determine obstacle value. Embankments more than 3 meters (10 feet) high with side slopes more than 45 percent can be serious obstacles. Cuts have similar significance. Large gravel pits, quarries, or areas where strip mining has taken place may present obstacles or traps for vehicles. Assess these also, particularly concerning slope and soil characteristics.

Streams and man-made drainage ditches that appear insignificant on a 1:50,000-scale tactical map may canalize or slow enemy movement. Reinforce and integrate these into the overall obstacle plan.

You can interpret most of the minor cultural features from air photos. Look for these on topographic maps. The features' dimensions, which directly affect cross-country trafficability, are difficult to determine from photos and maps. Thus, cultural feature information on cross-country movement is frequently available only through ground reconnaissance or from terrain teams.

(5) Climate. Climate and weather significantly affect cross-country movements. Their effects are usually indirect vary in duration, and are difficult to predict. One can usually see climatic influences in terrain and obstacles. Climate controls soil moisture and thus soil strengths. It also determines basic river and stream characteristics. Some easily overlooked direct effects of climate are important. Fog and smog, common in some areas, significantly affect weapons employment and can slow or even prevent movement. Dust storms and snowstorms have the same effect.

Seasonal weather patterns are important. Assess existing obstacles on the basis of the seasonal weather conditions to determine their obstacle value.

(6) Combined effects. The combined effect of terrain factors is far more important and considerably more difficult to define. Slopes combined with vegetation or soil conditions limit vehicular mobility far more than any single factor. The obstacle effect becomes clear long before any factors reach their critical values. The tank's weight magnifies the effect of even a slight rise by reducing its speed.

Even though a tank can push over a tree 25 centimeters (10 inches) in diameter on level ground, that same tree will stop the tank on a slight uphill slope. Further, the combined effect of several less-than-critical features or factors can stop armored vehicles.

Closely spaced trees much smaller than 25 centimeters (10 inches) in diameter also will stop a tank, even on level ground. The critical values previously discussed are the minimum requirements for halting movement. Lower values of slope or smaller trees, steps, ditches, and so on will severely slow the enemy's movement. A high frequency or density of features that are less than critical can severely reduce, although not stop, the enemy's movement. For example, a tank may eventually force its way through a densely cultivated forest that has not reached full growth. It will move forward only by repeated lunges and will have a very slow rate of movement. Every tanker knows how effectively a number of terraces or ditches, individually crossed, can interfere with movement. You do not need to completely stop enemy armored vehicles. Frequently, it is more desirable to slow him but not stop him. It is preferable not to stop enemy tanks if the goal is to lead enemy formations along a certain passage or in a particular direction. The same is true if the purpose is to lure enemy tanks into a desired engagement area (EA) to expose their less heavily armored flanks.

Also consider factors for more than obstacle effect. Consider slopes because of the limited depression and elevation it affords the tank's main gun. A steep cross slope also makes it difficult for rapid, accurate fire, giving the defender an advantage.

Finally, evaluate terrain factors when considering the movement of a combined arms formation and not just one tank. Threat forces attack in relatively fixed formations. Natural or cultural obstacles that stop or slow part of the formation will affect the movement of the entire formation, either to slow it or change its direction. This effect emphasizes the slowing ability of less-than-critical terrain factors or features. The effect of combinations and variations of natural or cultural obstacles makes their evaluation a complex skill. It requires experience and practice to develop its full potential.

2-2. Reinforcing Obstacles. Reinforcing obstacles (tactical and protective) are constructed, emplaced, or detonated to extend or improve existing obstacles.

a. Tactical Obstacles. Tactical obstacles are those obstacles employed to attack the enemy's execution of his plan. Emplace them on the battlefield where the enemy maneuvers from march, prebattle, and attack formations. Tactical obstacles reduce the enemy's ability to mass and reinforce while increasing his vulnerability to fire. They throw him off balance and make him vulnerable to exploitation. Mass tactical obstacles at critical points within zones and belts to bring about the commander's obstacle intent.

(1) Obstacle intent describes how, in terms of obstacle effect, the commander will use tactical obstacles to the advantage of his fire plan (direct and indirect) to affect the enemy's maneuver. The obstacle intent establishes a direct link with the obstacle and fire plans. Intent has three components: effect, target, and location. Further detail is provided in Lesson 3.

(2) The obstacle effect is conveyed through the use of precise graphics. Figure 2-2 shows the obstacle effects graphic symbols. Each symbol represents how the enemy's maneuver should be altered.

Figure 2-2. Obstacle effects symbols

Disrupt. Use disrupting obstacles to break up the mass that is essential to threat offensive tactics. These obstacles disrupt the enemy's march formation, break up his C², frustrate his timing and cause premature commitment of breaching assets. They also cause a separation between forward combat elements and trailing support elements. This allows the defender to attack the enemy's C² and exploit the low flexibility that exists at the motorized rifle battalion (MRB) level and below. In short, we want the enemy to piecemeal his force into our fires. Disrupt obstacles are generally used forward at the main EA.

Turn. Use turning obstacles to manipulate the enemy to maneuver in a desired direction. To entice the enemy to maneuver in the desired direction rather than breach the obstacle, the obstacle must have a subtle orientation. Likewise, the enemy must easily detect the bypass site to choose to bypass. The combination of obstacle and fires must be strongest at the cutting edge or where the turn begins. The start of the turn must be anchored to terrain or a strong point so that it cannot be bypassed.

Fix. Fix is the most misunderstood obstacle effect. Often, maneuver commanders use the term fix to mean stopping an enemy advance. However, the obstacle effect fix simply means to slow the enemy's rate of advance within a specified area so that he can be killed with fires. This effort can also generate the time needed to break contact. Employ fixing obstacles in depth to force the enemy to repeatedly breach. With each breach he loses momentum as well as breaching assets. The fixing obstacle cannot appear too tough to breach, thereby forcing the enemy to bypass. By its nature, fixing obstacles are most effective against line formations since a column formation will only require one lane to pass its force through the obstacle. Fixed obstacles are generally used in the main EA.

Block The last of the four tactical obstacle effects is block. Blocking obstacles are complex, employed in depth, and integrated with fires to prevent the enemy from proceeding along a certain AA. He may proceed, but only at an unacceptable cost. The obstacles themselves must defeat all possible breaching efforts, even complex obstacles that attack the enemy's breaching equipment. Blocking obstacles must be tied completely into the terrain so that there can be no bypasses.

(3) There are three types of tactical obstacles. They include directed, reserve, and situational.

Directed obstacles. The higher commander directs these obstacles as specified tasks to a subordinate unit. Units plan, prepare, and execute directed obstacles during the preparation of the battlefield. Most tactical obstacles are directed obstacles, and most directed obstacles are planned at TF level.

Reserve obstacles. Reserve obstacles are those obstacles for which the commander restricts execution authority. These are "on order" obstacles. The commander usually specifies the unit responsible for emplacing, guarding, and executing obstacles. Units normally plan and prepare reserve obstacles during the preparation of the battlefield. They execute them only on command of the authorizing commander, or based on specific criteria that the commander identifies.

Situational obstacles. Situational obstacles are obstacles that units plan, and possibly prepare, prior to starting an operation; however, they do not execute the obstacles unless specific criteria are met. Units, therefore, may or may not execute situational obstacles depending on the situation that develops during the battle. They are "be prepared" obstacles. They provide the commander flexibility for emplacing tactical obstacles based on battlefield development.

b. Protective Obstacles. Protective obstacles are obstacles placed in front of a units position to protect the force from enemy assault. They are also used in rear areas to slow infiltration. Emplace these obstacles close to the defensive position, cover them by direct fires, and tie them to final protective fires (FPFs).

Protective obstacles are a critical aspect of defensive operations. The defending force will usually install protective obstacles, allowing engineers more time to emplace tactical obstacles. Much like FPFs, protective obstacles provide the force with a combat edge. This may make the difference between success and failure during the enemy's final assault. Protective obstacles delay an attacker and allow the defender time to move to another battle position.

Protective obstacles complement the defender's fire plan. Orient them against the most severe close combat threat. For example, armored forces orient against dismounted forces. With protective obstacles, you must situate them according to terrain and always cover them by fire.

Install protective obstacles in support of a battle position and remove them when the position is no longer occupied. These are the only obstacles we can employ outside of appointed obstacle zones, belts, and groups. If you leave a position without recovering the obstacles, report their location through operational channels.

c. Types of Reinforcing Obstacles. Only imagination and logistics effort limit the extent of reinforcing obstacles. The types of reinforcing obstacles vary greatly from the massive systems constructed on the French coastline during World War II to a road crater emplaced by an engineer squad during Operation Desert Storm. Reinforcing obstacles also vary in emplacement methods and logistics and manpower requirements. Reinforcing obstacles fall into the following categories: demolition, constructed, land mines, contamination, and expedient.

(1) Demolition obstacles. Detonating explosives, including nuclear explosives, creates demolition obstacles. There are two types of demolition obstacles-preliminary and reserved. Preliminary demolition obstacles are not critical to the tactical commander's plan and do not require a formal written demolition order. You can detonate them immediately or as the tactical situation dictates. Reserved demolition obstacles are critical to the tactical commander's plan and require a formal written demolition order. Detonate demolition obstacles according to the instructions in the order. Typical uses of demolition obstacles include—

Blowing craters in roads, airfield runways, parking areas, and railroads.

Destroying bridges or tunnels.

Demolishing buildings to create rubble.

Flooding areas by destruction of dams or locks.

Crating abatis by tree blowdown.

Blowing ditches using solid or liquid explosives.

(2) Constructed obstacles. Constructed obstacles are those reinforcing obstacles built by soldiers and machinery, usually without using explosives. Constructed obstacles generally require extensive amounts of manpower, equipment, materiel, or time. Typical examples of constructed obstacles include—

Wire.

Tank ditches.

Log cribs.

Nonexplosive abatis.

Steel H-beam post obstacles.

Falling or tumble blocks.

Dragon's teeth, hedgehogs, and tetrahedrons.

Soldiers and construction equipment face exposure to all types of enemy fire when emplacing constructed obstacles. Emplace constructed obstacles before the battle starts or along a terrain feature away from the direct EAs. Otherwise, observed fire can disrupt the emplacement process.

(3) Land-mine obstacles. Land-mine obstacles enhance the hit-and-kill probabilities of AT weapons. Mines and minefields perform this function as well as killing or destroying enemy vehicles and personnel. Mines fall into two groups--conventional and scatterable. They are grouped by capabilities, employment techniques, and delivery means. Both groups of mines have a distinct place on the battlefield and complement each other.

Conventional mines. Conventional mines do not self-destruct. Directly emplace conventional mines by hand or mechanical mine-planting equipment. Bury or surface-lay them with or without regard to pattern depending on the tactical situation.

Scatterable mines do self-destruct after a set time. Scatterable mines have added a new dimension to mine warfare and the battlefield. The traditional concept of large, linear minefields across contested areas is no longer viable, except possibly in desert warfare. Future battlefields will contain many smaller mined areas placed in response to enemy disposition and movement. Employ scatterable mines against enemy units anywhere on the battlefield. Scatterable mines can be emplaced by a variety of delivery systems, including mechanical and explosive ground systems, artillery, helicopters, and high-performance aircraft. This significantly reduces manpower requirements associated with mine warfare. Scatterable mines are also smaller, lighter, and more lethal. They offer a reduction in logistics requirements due to reduced bulk and weight.

Since all scatterable minefield systems provide more flexibility to maneuver commanders, there will be extensive demand for them. Commanders and engineers should plan and carefully assign priorities. Use available systems only for the most critical needs. Closely coordinate their employment with obstacle plans, fires, and the scheme of maneuver. Coordination with fire-support planners, aviation staff officers, and air liaison officers is essential. This ensures prior planning to execute minefield emplacement missions on short notice. Planning and employing scatterable mines will be discussed in Lesson 4.

(4) Contamination obstacles. Contamination obstacles can be either nuclear or chemical in nature. Both types are difficult to predict and control because they depend on winds for placement. They are also subject to weather and other environmental factors. The US has renounced the first use of chemical weapons. Further, the most predictable source of nuclear contamination—atomic demolition munitions (ADM)—is subject to the same restrictions as all nuclear weapons. It may not be available for use when needed. If you use an ADM for cratering, there will be close-in radiation and fallout. This will effectively contaminate an area to a reasonably predictable extent. Threat doctrine considers the use of nuclear and chemical weapons and trains for operations in contaminated areas.

(5) Expedient obstacles. The potential of expedient obstacles is almost unlimited. They place a high premium on imagination and ingenuity in the use of available materials and other resources. This avoids the logistics burden associated with all other types of obstacles. We can build a variety of nonstandard log obstacles. Their complexity depends on the time and personnel available. Spread junked or destroyed cars and trucks or other debris to block an open area. If the region is rocky, use earth-moving equipment to distribute boulders to block tanks. Push or pull selected trees over to make an abatis. This will also strengthen a wooded area where tree spacing might otherwise allow armored vehicles to pass. Cut short ditches in lieu of craters. Push material up to form a road block. Steepen or deepen stream banks, gullies, or other breaks in the terrain to make tank ditches. Use the M9 armored combat earthmover (ACE), dozers, loaders, and many other pieces of equipment (see Figure 2-3).

The wreckage of destroyed towns, cities, or industrial areas offers a source of materials for making expedient obstacles. If permitted, use limited, controlled flooding to inundate areas. Also, create soft or slippery areas where soil conditions make this possible. Burn timber bridges and use controlled fires to create other obstacles. For example, igniting the brush in a brush-filled ditch at the proper time can make an effective obstacle. If available, use ice and snow to create effective obstacles.

By their nature, expedient obstacles substitute locally available materials and soldier labor for a logistics requirement. Use your imagination to recognize the potential of available materials.

Figure 2-3. Expedient tank obstacles

PART B: GUIDELINES OF TACTICAL OBSTACLE EMPLOYMENT

Army operations, the Army's current fighting doctrine, offers the commander fighting the battle a complete range of defensive options. He can use an area defense to focus on terrain retention or to use firepower from fixed positions to deny terrain. He may adopt a mobile defense that focuses upon maneuver to destroy enemy forces rather than retain specific terrain.

The area and mobile defensive frameworks are the extremes of the spectrum. Typically, the commander may combine both the area and mobile forms in organizing the defense. He bases his decision upon METT-T factors.

Whatever the concept, the maneuver commander must carefully organize the defense to match the terrain. The engineer is the principal element in reinforcing the terrain to best complement the maneuver commander's plan. The engineer and the maneuver commander must coordinate throughout the planning and battlefield preparation sequence. This ensures unity of effort and maximum effectiveness of obstacle employment.

2-3. Employment. Employ terrain reinforcement techniques throughout the depth of the defensive AO, especially along AAs. Tactical obstacles are the principal method of terrain reinforcement. Tactical obstacles have the following purposes:

Enhance the effectiveness of friendly direct and indirect fires.

Delay the enemy's advance, upset his timing, disrupt his formations, and delay or destroy follow-on formations.

Maneuver the enemy into a position of disadvantage.

Enhance friendly economy-of-force measures.

Cover all obstacles by fire. Locate tactical obstacles within the effective range of friendly direct-fire AT weapons, whereas protective obstacles are generally located within range of their greatest close combat threat weapons. Carefully coordinate their locations with the location of battle positions and direct- and indirect-fire weapons.

Engage the enemy at the maximum effective range of AT weapons. Force him to breach and fight his way through a series of obstacles while under intense fire. Each obstacle delays some part of the enemy's leading elements.

The coordinated use of obstacles delays and disrupts enemy formations. It also forces them into the primary fields of fire of our tanks and other AT weapon systems. In addition to preventing his escape from such an EA, this forces the enemy to move on the battlefield in conformance with the friendly commander's plan.

The skillful use of obstacles to canalize the enemy is a vital factor. Once the enemy force maneuvers into the EA, it is held there by other groups of obstacles. Other obstacles may be used to close the trap behind it. Scatterable mines are ideal for the latter purpose. Use other obstacles to separate the enemy's leading elements from reserves or follow-on formations. This precludes reinforcement.

Mutually-supporting obstacles serve other important purposes. Use them in the economy-of-force role to strengthen a naturally-strong existing obstacle area so that it only needs to be lightly defended. This frees forces to concentrate elsewhere. Similarly, use obstacles with mobile forces to protect flanks and other lightly defended areas. This is a particularly important role in view of the threat doctrine of penetration and envelopment and the overall dispersion of forces on the battlefield.

Regardless of the type of defense employed by the tactical commander, some basic employment guidelines for obstacles include the following:

Support the maneuver commander's plan.

Integrate with observed fires.

Integrate with existing obstacles and other reinforcing obstacles.

Employ in depth.

Employ for surprise.

a. Support the Maneuver Commander's Plan. Plan and emplace obstacles to support the tactical plan. Obstacles, other than mines, emplaced outside the range of friendly weapons are of little use. Engineers must familiarize themselves with the tactical plan, existing terrain, and maneuver commander's intentions. Only then can they fully realize the value of integrating obstacles and fires.

b. Integrate With Observed Fire. Use obstacles to develop EAs in which we want to restrict and slow enemy maneuver. This increases the hit probability of friendly direct and indirect fires. The tactical commander and the engineer site the weapons and obstacles where they offer the best relative advantage. They consider terrain configuration and the weapon's effective range. Give special attention to locating obstacles to complement the fires of dragons, tanks, and tube-launched, optically tracked, wire-guided (TOW) missiles. TOW command-link missiles have a longer maximum-effective range than threat tanks. It is advantageous to site part of the tactical obstacle system to capitalize on that difference. Normally, the greatest relative advantage accrues when the obstacle is at the maximum range possible and consistent with visibility conditions and the tactical plan (see Figure 2-4).

Observed indirect fires are integrated with obstacles against enemy vehicles and infantry out in the open. Observing and adjusting fires are essential in developing full advantage of any situation. At the same time, fires serve to protect the obstacle by making it costly to breach or bypass them. With rare exceptions, obstacles not covered by fires are little more than a nuisance to the enemy's leading elements.

Integrating obstacle locations with fires enhances the effectiveness of fires. This is a significant combat-multiplier effect of obstacle use.

Figure 2-4. Integrating obstacle and weapon

(1) Disrupt/direct-fire integration. The integration of direct fire with disrupting obstacles uses the combination of indirect fires and obstacles to cause the enemy to deploy early. It slows a portion of the attacking formation. Direct fires are massed on the obstacle effect. This requires the use of lethal and relatively long-range weapons positioned to mass fires on undisrupted portions of the formation. Shift fires on the obstacle if it appears that it is being breached too quickly (see Figure 2-5). Disrupt/direct-fire integration has the following characteristics:

Causes the enemy to deploy early.

Requires use forward of or within EAs.

Uses indirect fires to cover the obstacle. It may be a suppress or neutralize artillery fire mission.

Allows both direct and indirect fires to shift in order to cover the obstacle if easily breached.

Requires a quick, lethal blow with direct fires.

Figure 2-5. Disrupt/direct-fire integration

(2) Turn/direct fire integration. The direct-fire integration with turning obstacles centers around two principles. First, mass high columns of lethal direct and indirect fires at the turning point. Massing fires here is a mission-critical task. If the enemy breaches the obstacle at the turning point, friendly forces will not achieve the desired effect. In this case, the enemy often will flank the force covering the obstacle. Second, there must be enough direct and indirect fires available to shift with the turning effect. Hence, direct- and indirect-fire control must mass fires at the turning point. They must also shift fires to maintain pressure on the turning enemy formation. Often, it requires dismounted infantry, restrictive terrain, or a combination of both to anchor the turning obstacle (see Figure 2-6). Turn/direct-fire integration has the following characteristics:

It is anchored by a combination of massed fires, terrain, or infantry.

Its anchor point may be a destroy artillery fire mission.

Its direct/indirect fires shift with turning formation to maintain pressure.

Its fires must force the turn in the desired direction.

Its FPF and final protective line (FPL) are tied into the anchor point to prevent bypass.

Figure 2-6. Turn/direct-fire integration

(3) Fix/direct-fire integration. The direct-fire integration with the fixing obstacle has fires and obstacles employed in depth. Begin both fires and obstacle effect concurrently. Use forces to bring the enemy on line rather than in columns, which is his best breaching formation. Fires and obstacles become more intense the further the enemy advances within the fixing obstacle group. Use indirect fires or force positioning to prevent enemy bypass. Use direct-fire control measures, such as trigger lines, to control direct and indirect fires (see Figure 2-7). Fix/direct-fire integration has the following characteristics:

It causes the enemy to deploy into attack formation early.

Its obstacle effect and fires are initiated simultaneously; the obstacles/trigger line is sited.

Its fires gain intensity as the enemy advances in order to slow him in the EA.

The depth of the system equals the depth of weapons.

It uses indirect fires to contain bypasses.

The obstacle may or may not provide flank shots.

Its indirect fires may be a neutralize artillery fire mission.

It makes the enemy fight in multiple directions.

Figure 2-7. Fix/direct-fire integration

(4) Block/direct-fire integration. The direct-fire mission-essential task is to protect the obstacle's integrity. All forces concentrate on destroying breaching assets to prevent the enemy from advancing through the EA. Target the blocked formations with other means such as counterattack (CATK) forces, close air support (CAS), or a joint air attack team (JAAT) (see Figure 2-8). Block/direct-fire integration has the following characteristics:

All fires are massed within the confines of the obstacle group across the AA.

All forces concentrate on destroying breaching assets.

Blocked enemy formations are targeted by other weapons or forces (CAS, artillery (ARTY), or CATK).

Indirect fires may be a destroy artillery fire mission.

Figure 2-8. Block/direct-fire integration

c. Integrate With Existing Obstacles and Other Reinforcing Obstacles. Site reinforcing obstacles to take maximum advantage of existing obstacles. Emplace them where they close the gaps between existing obstacles. Destroy the road network and disrupt the inherent natural pattern of cross-country movement. Plan bridge demolitions, road craters, abatis, and point or small minefields that tie together the existing obstacle areas first. Locate other tactical obstacles to strengthen and extend the existing obstacle areas and block major corridors. Taking advantage of the existing obstacles reduces the resources required to quickly build an effective obstacle system. Effective reinforcement of existing obstacles also enhances economy-of-force operations. It permits friendly forces to concentrate on more trafficable terrain approaches.

Site individual obstacles to tie in with existing obstacles (see Figure 2-9) or with each other. An obstacle that the enemy can bypass immediately is worthless. Carefully design each obstacle for the exact location it will occupy. It must overlap on each side with the existing obstacle it will complete. The critical design width of an obstacle is the distance from an existing obstacle to another existing obstacle (or to another reinforcing obstacle). It is not the width of a road or highway through the existing obstacle.

Figure 2-9. Integrating reinforcing obstacles

Another major design consideration is that the tactical obstacle does not need to be stronger than the existing obstacle. If the enemy could force his way through the existing obstacle in 10 minutes, it would be wasteful to construct a tactical obstacle requiring 40 minutes to breach. We could use the effort and resources used to force that last 30 minutes of breaching elsewhere. Determining the delay or breaching time associated with a particular obstacle may be difficult. Nevertheless, keep this principle in mind to make the most use of available resources.

Integrate tactical obstacles with each other to close probable bypass routes. For example, destruction of a major highway through a wooded area is largely ineffective if you leave open any nearby roads or openings that offer a ready bypass route. Such destruction is highly effective, however, if friendly forces seek to divert the enemy along that bypass route. Always attempt to close gaps and lanes in tactical obstacles. For example, use a crater to close a road left open through a minefield when all friendly troops have cleared.

d. Employ in Depth. Use a series of simple obstacles arranged one behind the other along a probable axis of enemy advance. This is far more effective than one large, elaborate obstacle. Restricting the obstacles' design to correspond with the strength of the existing obstacle (as previously discussed) helps to conserve effort. It also directs this effort toward executing obstacles in depth. Do not locate obstacles too close to that only a single enemy response is required. Locate them far enough apart so that each will require a new deployment of the enemy's counterobstacle forces and equipment. The distance between obstacles will depend on the terrain and the obstacle effort available. Proper use of obstacles in depth wears the enemy down and significantly increases the overall delay. At each new obstacle, the enemy incurs losses and is forced to stop and react. This wearing-down effect is psychologically significant. The desired effect degrades the enemy soldier's will and induces a feeling of hopelessness. Do this by convincing him that beyond each new obstacle awaits yet another obstacle with a similar cost.

Another reason to use a larger number of less elaborate obstacles is to expose the enemy's limited counterobstacle equipment and troops to loss. Each time we wreak havoc with the enemy's counterobstacle resources initially allotted to the leading elements, it slows the enemy's movement severely until he brings new counterobstacle units forward.

e. Employ for Surprise. A commander uses obstacles to gain surprise and retain a degree of initiative even when defending. Scatterable mines permit rapid mining anywhere in the battle area. This confronts the attacker with a completely new situation almost instantly. The self-destruct feature of the scatterable mine also provides surprise. A friendly commander can counterattack through an area that was mined prior to the attack after the mines self-destruct.

More conventional ways to gain surprise, such as using the reverse slope of terrain, are also available. They include the sudden detonation of concealed obstacles in front of the attacking enemy or within his formations. Conventional ways also include the use of dummy obstacles to mislead the enemy about the pattern and extent of the friendly obstacle system. An obvious pattern of obstacles would divulge locations of units and weapons. Friendly forces must avoid readily discernible, repetitive patterns. We must make our obstacle system more difficult by varying the type, design, and location of the obstacles. Extensive use of obstacles can contribute to this effort.

2-4. Summary. We classify obstacles as either existing or reinforcing. Existing obstacles are natural or cultural. They are a part of the terrain when battle planning begins. The ability to recognize and assess the terrain's obstacle potential is critical to planning the battle. Reinforcing obstacles are either tactical or protective. Construct, emplace, or detonate tactical obstacles to knit together, strengthen, and extend existing obstacles. Integrate tactical obstacles with friendly observed fires and the maneuver plan. Arrange tactical obstacles in depth and employ them for surprise.

Mines are one of the most effective type of obstacle because they inflict losses on the enemy and their use is highly flexible. The family of scatterable mines (FASCAM) vastly increases this flexibility, making the creation of rapid minefields possible. Use obstacles to delay and disrupt an attacking force as well as to upset the enemy's timing and plans. This should divert him into EAs where we can destroy him. Obstacles delay or destroy follow-on formations. Obstacles significantly enhance the effectiveness of our fires and thus our ability to win the battle.

Practice Exercise