Chapter 2. COUNTERMOBILITY FUNDAMENTALS. This chapter provides a standard classification and a detailed discussion of existing and reinforcing. Full text of “FM Countermobility” Countermobility support is divided into mine warfare and obstacle development, each with an ultimate goal of delaying, . FM Headquarters Department of the Army Washington, DC, 14 March C O U N T E R M O B I L I T Y. he foundation for engineer doctrine in .

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There are many countermobility assets and methods at the commander’s disposal. This chapter describes the countermobilitty and execution of countermobility activities other than minefields. Employing all types of obstacles will provide flexibility to vountermobility commander and increase the variety of obstacles that the enemy must encounter.

Streams and rivers are formidable obstacles to mobility. In most developed countries of the world, bridges have been constructed to span these waterways along lines of communication. Generally, roads and railroads also follow what would be likely military avenues of approach. The -5102 of existing bridges is critical to the mobility of a military force. Without existing bridges, forces must conduct river crossings using tactical bridging.

A river crossing operation is one of the most difficult operations to perform successfully as it normally requires extensive time and resources. By demolishing or rendering existing bridges unserviceable, we can force the enemy to use time and resources to conduct tactical river crossings. The vulnerability of the enemy is greatly increased during river crossings and presents a good opportunity to destroy his forces. Bridge destruction cannot be accomplished haphazardly.

There are several very important factors that countermoility be considered and planned such as:. Only that portion ccountermobility the bridge essential to accomplish the military objective should be destroyed. In some instances where the span is short or the bridge has no intermediate supports, destruction of the entire bridge may be required. In other instances where the bridge is large, dropping a single span may prevent enemy use, conserve demolitions, and make the bridge easier to reconstruct at a later date.

Enemy capability must be a prime consideration in making this decision. The answer to this question is tactically dependent. Had the Germans countermobliity the Remagen bridge several days earlier, many of their problems would not have occurred.

Countermobility on the Battlefield

At the same time, they may have isolated some of their forces on the far bank. If a bridge is blown too early, it may give the enemy time to change direction countermobipity therefore not impede his mobility at all. Waiting too long may enable the enemy to capture the bridge intact. The commander must make this tough decision only after considering the factors involved.

The location of friendly forces and future plans of the command are prime factors. Coordination is required with higher, lower, and adjacent units, as well as other services in many cases.

FM -Countermobility –

A worst case example would be for air assets to prematurely destroy a bridge that would be a major avenue of approach for a ground counterattack. Major bridge destruction requires substantial amounts of time, personnel, and explosives.

Planning and coordinating must occur early to insure that resources are available and targets are executed at the proper time. Unnecessary destruction of bridges has a major impact upon the local population. As with any other denial target, care should be taken to minimize that impact. Craters are effective obstacles to enemy movement when constructed properly and located at critical points along his movement route.

Craters are normally placed on roads or other high speed movement routes the enemy is expected to use. They should be placed at locations that cannot be easily bypassed such as cuts or fills.

The basic purposes are to delay or stop the enemy, cause his forces to bunch up and provide good targets, and force him to use up breaching assets such as bridging and earthmoving equipment. Use of antipersonnel and antitank mines in conjunction with craters creates formidable obstacles.


Craters should be placed in depth to prevent the enemy from conducting a single breach and continuing on. There are essentially two placement methods:. This method makes the obstacle extremely difficult to breach by earthmoving equipment and by a tracked-vehicle launched bridge. The loose soil will cause the bridge to rest unevenly, and exiting vehicles will have no place to go except into an adjoining crater.

When using this method, care conutermobility be taken during the demolition process so that soil blown from one crater does not come to rest in adjacent craters and thus reduce their obstacle value. This method forces the enemy to conduct several breaches. In any case, craters should be tied into existing or reinforcing obstacles and covered by direct fire weapons. To be effective obstacles, craters must be too wide to be spanned by tracked vehicles, and too deep and steep-sided for any other vehicle to pass through them.

Blasted road craters will not stop modern tanks indefinitely, because repeated attempts by the tank to traverse the crater will pull loose soil from the slopes of the crater into the bottom, reducing both crater depth and slope angles.

Road craters must be large enough to tie into natural or man-made obstacles at each end. The effectiveness of craters may be improved by placing log hurdles on either side, digging the face nearly vertical on the friendly side, and mining the site with antitank and antipersonnel mines.

Wire placed in the crater will add to the difficulty of mine clearing. All military explosives may be used for blasting antitank craters. A special pound cratering charge ammonium nitrate issued in a waterproof metal 5-120 is specifically designed for blowing craters and, if available, should be used with the conventional method.

The M kit comes complete with explosive. A hasty road crater is emplaced when time and explosives are limited.

It is not as effective as the deliberate crater, which will be described later. The hasty cratering method produces a crater 6 to 7 feet deep, and 20 to 25 feet wide with side slopes of 25 to 35 degrees.

In forming a hasty road crater, all boreholes must beat least 5 feet deep, each loaded with at least 50 pounds of explosive. Following are the steps necessary to blow a hasty crater. Space the boreholes 5 feet apart starting at the center of the roadway and extending in each direction of the desired crater. This cratering method produces road craters which are more effective than those resulting from the hasty method but require more time and explosive.

The deliberate method produces a deeper 7 to 8 feetwider 25 feetand steeper-sided 30 to 37 degrees crater than the hasty method. The calculations for a deliberate crater are the same as a hasty crater with the following exceptions:. This cratering method produces road craters that are more effective obstacles to modern tanks than the hasty or deliberate method, but they require still more time and explosive than the hasty or deliberate.

This technique produces a trapezoidal-shaped crater about 7 feet deep and 25 to 30 feet wide with unequal side slopes. In compact soil such as clay, the relieved face cratering method will provide an obstacle shaped as shown in the top viewbelow.

The side nearest the enemy slopes at about 25 degrees from the road surface to the bottom, while that on the opposite or friendly side is about 30 to 40 degrees steep.

Countermobilitty exact shape, however, depends on the type of soil found in the area of operations. The procedure is as follows:. On dirt or gravel-surfaced roads, drill or blast two rows of boreholes 8 feet apart, spacing the boreholes on 7-foot centers.

On hard-surfaced roads, drill the two rows 12 feet apart. The number of charges for the friendly side rm can be calculated by the formula:. Any fractional number countermobikity holes should be rounded UP to the next highest number. Stagger the boreholes in the row on the enemy side in relationship to the other row, as shown 5-1102 the sideviewfn. The enemy side row will always contain one less borehole than the row on the friendly side. Make the boreholes on the friendly side 5 feet deep and load with 40 pounds of explosive; on the enemy side, 4 feet deep and load with 30 pounds of explosive.


Prime the charges in each row separately for simultaneous detonation. Best results will be obtained if the charges on the friendly side are fired while the earth moved in the first row is still in the air. Standard delay caps may be used for delay detonation.

If adequate means for sufficient time for delay firing countermobilihy not available, acceptable results may be obtained by firing both rows simultaneously.

FM 5-102 Countermobility

However, the resulting crater will not have the same depth and trapezoidal shape as previously described. To prevent misfires from the shock and blast of the row of charges on the enemy side detonated firstthe detonating cord mains and branch lines of the row on the friendly side detonated last must be protected by a covering of about 6 inches of earth. This method is useful against tanks traveling in defiles or road cuts where they must approach the crater straightway.

The road crater is blasted using either the hasty or deliberate cratering methods, except the boreholes are drilled across the roadway at about a degree angle as shown. Because of the angle tanks must attempt to cross, they tend to slip sideways and ride off their tracks. Boreholes for cratering charges may be dug by using motorized post hole augers or handheld post hole augers or diggers, or blasted using shaped charges. Making the boreholes is normally the most time-consuming task related to cratering.

Hard-surfaced pavement of roads and airfields is breached so that holes may be dug for cratering charges. This is done effectively by exploding tamped charges on the pavement surface. A 1-pound charge of explosive is used for each 2 inches of pavement thickness. The charge is tamped with material twice as thick as the pavement. Boreholes which have been drilled or blasted through pavement and contain placed charges can also breach pavement.

A shaped charge readily blasts a small diameter borehole through the pavement and into the subgrade. Concrete should not be breached at an expansion joint because the concrete will shatter irregularly. Standard shaped charges may be used to blast boreholes in both paved and unpaved surfaces for rapid road cratering with explosives. For maximum effectiveness, M3A1 shaped charges should be used to blast boreholes in thick, reinforced concrete pavements laid on dense highstrength base courses.

The M2A4 shaped charges may be used effectively to blast cratering charge boreholes in reinforced concrete pavement of less than 6-inch thickness laid on thin base courses, or to blast boreholes in unpaved roads.

Full text of “FM Countermobility”

Almost all types of military explosive, including the cratering charges, can be loaded directly into boreholes made by the M3A1 and M2A4 shaped charges. Shaped charges do not always produce open boreholes capable of being loaded directly with 7-inch diameter cratering charges without removing some earth or widening narrow areas. Many boreholes having narrow diameters but great depth can be widened simply by knocking material from the constricted areas with a pole or rod, or by breaking off the shattered surface concrete with a pick or crowbar.

For road cratering on asphalt or concrete-surfaced roadways, blasting the boreholes with shaped charges will expedite the cratering task by eliminating the requirement for first breaching the pavement with explosive charges.

A good rule couhtermobility thumb is to increase by one-and-one-half to two times the number of boreholes and charges from those calculated by standard formulas for moderate climates. Frozen soil, when blasted, breaks fk large clods 12 to 18 inches thick and 6 to 8 feet in diameter.