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Appendix A

Individual Obstacles

This appendix contains a description of the different types of individual obstacles. Also, there is a discussion of individual obstacle designs and how to develop individual obstacles. Lastly, this appendix describes the array of individual obstacles to support the obstacle effects.


Only the imagination and ingenuity of the soldier who designs and emplaces them limits the nature and extent of reinforcing obstacles. The general types of individual obstacles are--

  • Demolition obstacles.

  • Constructed obstacles.

  • Land mines.

  • Improvised obstacles.

  • Complex obstacles.

In addition, there are phony obstacles, which are not a type of individual obstacle but are representations of actual obstacles that units use to deceive the enemy.


Units create demolition obstacles by the detonation of explosives. There are many uses for demolitions, but some examples are--

  • Destroying bridges.

  • Creating road craters.

  • Creating abatis.

FM 5-250 covers demolitions and the effects of demolitions in detail.


The use of existing bridges is critical to the mobility of a military force, especially bridges spanning nonfordable rivers and streams. Demolishing bridges forces the enemy to search for a suitable bypass (another bridge or ford site at a different location) or expend mechanical assault bridging assets to maintain its momentum.

There is no standard planning factor for the destruction of bridges as many variables impact on the materials and the manpower required. See Chapter 4, FM 5-250, for details. The maneuver commander decides whether to order a complete or a partial bridge demolition. The complete bridge demolition leaves nothing of the old structure, while the partial demolition saves the near-side spans and abutments. The partial demolition permits easier reconstruction of the bridge.

Road Craters

An RC is an effective obstacle on roads or other high-speed-movement routes, such as firebreaks. The RC forces the enemy to use earthmoving equipment, blade tanks, or mechanical bridging assets. Generally, there are two types of RCs, hasty or deliberate. The planning factors and material requirements for RCs are in Chapter 3, FM 5-250. See Figure A-1 for an example of the use of an RC.

Figure A-1. Road crater.


Abatis are only effective if large enough trees are available to stop the enemy force. Abatis can be useful on roads and narrow movement routes. Refer to Chapter 3, FM 5-250, for more information. See Figure A-2 for an example of the use of a standard abatis.

Figure A-2. Abatis.


Units create constructed obstacles with manpower or equipment and without the use of explosives. Examples of constructed obstacles are--

  • Wire obstacles.

  • Tetrahedrons and hedgehogs.

  • Antitank ditches.

Wire Obstacles

Wire obstacles typically target the dismounted threat. Triple standard concertina is a common wire obstacle; however, there are other types, such as double apron, tanglefoot, and general-purpose barbed-tape obstacles (GPBTOs). Double apron is manpower and material intensive and units typically use it only for deliberate protective obstacles. Tanglefoot works well in tall grass or along a low-water line. The GPBTO is an extremely effective wire obstacle, and soldiers can emplace it from a vehicle. Refer to Chapter 3, FM 5-34 for more information. See Figure A-3. for an example of standard wire obstacles.

Figure A-3. Wire obstacles.

Tetrahedrons and Hedgehogs

Tetrahedrons and hedgehogs target the mounted threat. Tetrahedrons are pyramids with a triangular base and are normally about 1 meters on each side. Engineers fabricate tetrahedrons from steel beams or use concrete to create a massive tetrahedron. Engineers construct hedgehogs from three or four steel beams joined in the middle to create something similar to a child's giant jack. Both of these obstacles are effective in restrictive terrain. Units commonly use them in urban areas. Their ability to completely stop light vehicles makes them ideal for use in protective obstacles around fixed sites in OOTW.

Antitank Ditches

Units can also use equipment to alter terrain to create constructed obstacles. For example, an AD is a constructed obstacle that is effective against all types of vehicles. Like minefields, ADs are linear obstacles, but they require that the enemy use a different breaching asset than it does for minefields. Additionally, mine-plow- and roller-equipped tanks cannot cross a breached AD as easily as a normal tank can. There are two basic AD designs, rectangular or triangular (see Figure A-4).

The AD supplements turn or block obstacle groups. Units normally do not use ADs for disrupt or fix obstacle groups because of the time and equipment requirements. The commander must realize that the construction of ADs is time and equipment intensive. Typically, there is a trade-off between digging ADs and digging survivability positions.

Figure A-4. Antitank ditches.


Mines are explosive devices emplaced for the express purpose of killing, destroying, or otherwise incapacitating enemy personnel and equipment. Mines affect the enemy in two ways. The first is the damage they inflict on enemy personnel and equipment. Second, mines have a psychological impact. Units that detect mines, or witness the mine effect on other parts of a formation, tend to slow down and seek bypasses to avoid the mine effects. The two general categories of land mines are--

  • Conventional mines.

  • Scatterable mines.

Conventional Mines

Conventional mines are hand-laid mines that require manual arming. Conventional mining is resource (time, labor, supply, and transportation) intensive. Part One, FM 20-32, covers conventional mines and mining in detail.

Scatterable Mines

SCATMINEs are laid without regard to classical pattern and are delivered by aircraft, helicopter, artillery, missile, or ground dispenser. SCATMINEs provide the maneuver commander a flexible, responsive, and lethal mine-laying capability to affect the enemy's ability to maneuver. All US SCATMINEs have a limited active life and self-destruct at a preset time. The duration of the active life depends on the type of mine and delivery system.

SCATMINEs are not an obstacle cure-all for inadequate tactical planning. Their use requires extensive coordination, integration, and control. Indiscriminate use of SCATMINEs causes a rapid depletion of valuable assets. More importantly, the poorly planned use of SCATMINEs can impede friendly movement and cause fratricide. For more detailed information on SCATMINEs and systems, refer to Part Two, FM 20-32.


Soldiers and leaders design improvised obstacles with imagination and ingenuity when using available materials and other resources. Possible improvised obstacles include the following:

  • Rubbled masonry buildings.

  • Controlled fires.

  • Flooded areas created by opening floodgates or breaching levees.

  • Damaged vehicle hulks used as roadblocks.


Units can create complex obstacles to improve the effectiveness of obstacle groups. Complex obstacles are a combination of different types of individual obstacles. For example, an RC reinforced with AT mines is a complex obstacle. The RC requires that the enemy employ its mechanical bridging or blade-breaching assets, while the AT mines require that the enemy use a mine-breaching asset. Together, the RCs and mines create a better obstacle. The key to creating effective complex obstacles is knowing the quantity and capability of the enemy's breaching assets.

A complex obstacle should affect low-density breaching equipment first; then it should affect more common breaching equipment. For example, if the enemy has nine mine plows and three blade tanks, the unit can use an AD and mines to force the enemy to use both breaching assets. This increases the time required to breach. Moreover, by putting the AD before the mines, the enemy must use its lowest density breaching equipment first. If friendly forces destroy the blade tanks, they reduce the probability of the enemy breaching the complex obstacle.

Another example of complex obstacles is using AP mines, triple standard concertina, tanglefoot, and AT mines. The wire and AP mines strip the enemy's dismounted infantry away from assaulting tanks. This makes both more vulnerable and enables the defending force to concentrate on one type of threat. The AT mines prevent armored vehicles from dashing through the wire unimpeded.


Phony obstacles play a key role in obstacle protection by helping hide a unit's actual obstacles from the enemy. They can also help a unit compensate for shortages of obstacle resources. A unit can mix actual obstacles with phony obstacles within an obstacle group. Naturally, this implies risk, and commanders must ensure that they consider the risk of using phony obstacles.

Commanders must also ensure that the emplacing unit creates a phony obstacle that will have the desired result on the enemy. An example is a shallow excavation combined with a loose soil berm to simulate an AD. Another technique is to use minefield markings where there are no minefields. To be successful, this technique normally requires that the unit establish a precedent. Highly visible minefield markings in a disrupt obstacle group in forward areas provide a visual cue to the enemy concerning minefields. Using the same markings without minefields in a fix obstacle group may cause the enemy to assume that there is an actual minefield where none exists.


The remainder of this appendix provides guidelines for individual obstacles. Units use individual obstacles as building blocks for obstacle groups. Standard obstacles allow rapid estimating for resourcing (time, manpower, equipment, and materials) that is critical in making the force's obstacle effort effective, efficient, and timely. They allow units to train on the installation of individual obstacles as drills.

FMs 5-34, 5-102, and 20-32 provide details on specific standard obstacles.

These standard obstacles are not the only types of obstacles that units should consider. Instead, units should consider modifying standard obstacles or creating their own standard obstacles based on METT-T and other resource availability. For example, the standard minefields in FM 20-32 are focused on a soviet-style tank and motorized infantry threat. These minefields may not be appropriate for a mixed force of light infantry and tanks.

The following paragraphs provide some basics for designing minefields based on the type of threat.


Units may need to design minefields for armor threats other than soviet-style forces. The next few paragraphs describe some considerations for designing minefields based on an enemy with armor companies of 12 to 18 combat vehicles. These are minefields that a unit can use as building blocks for obstacle groups in mostly open terrain.


An enemy armored company of 12 to 18 combat vehicles will have a probable frontage of 500 meters when deployed. To affect the enemy, half the enemy company frontage (250 meters) should encounter the minefield. An individual obstacle of 250 meters frontage is an appropriate-size building block.


Minefields must have enough depth to support the obstacle effect based on the enemy's breaching capability. If the commander wants a disrupt or fix effect, the minefield should require the enemy to expend at least one breaching asset (for example, 100 meters if the enemy has a mine-clearing line charge (MICLIC)). For the turn-and-block effect, the depth should increase to force the enemy to expend more breaching assets. For an enemy not equipped with line charges, the depth can decrease. If the enemy has no mechanical breaching assets, the depth can decrease even further.

Antitank Mines

The two options are track-width and full-width fuzed AT mines. Compared to the full-width fuzed mines, track-width fuzed mines have a lower probability of encounter. Track-width fuzed mines require a density of 1.0 per linear meter of front; however, adding one row of full-width fuzed mines can reduce the resources required while increasing the probability of encounter for the minefield. This results in one row of full-width fuzed mines and two rows of track-width fuzed mines.

Antipersonnel Mines

The minefield focuses on the mounted threat, so if the enemy has mounted breaching assets, AP mines normally will not make much of a difference. However, if the enemy lacks mechanical breaching assets, adding AP mines can help prevent dismounted breaching.

Antihandling Devices

The emplacing unit determines the requirement for AHDs based on the threat. Normally, units use AHDs only if they expect covert or other dismounted breaching attempts.

Irregular Outer Edges (IOEs)

The purpose of IOEs is to confuse the enemy about the orientation of the minefield and to increase the probability of an encounter. There may be cases where an IOE is desirable, such as a fix or block effect. The IOE does not have to be part of the standard minefield.


Designing standard minefields to achieve a specific obstacle effect against a light force is a unique challenge. There are no strict doctrinal frontages associated with an enemy light infantry company; however, a typical march formation for a dismounted infantry company has a frontage of 40 to 200 meters. The following paragraphs describe considerations for designing standard minefields for a light threat.


An enemy infantry company typically consists of three platoons. In march (column) formation, it has a frontage of 40 to 200 meters. Using 200 meters as the enemy's maximum frontage, the standard minefield must target half of its frontage (100 meters). Camouflaging the mines and total pattern aids tremendously in increasing the effectiveness of the disrupt and fix minefields.


A 45-meter depth complicates a light infantry's breaching attempt. A light force employs grapnel hooks, hand-placed explosives, bangalore torpedoes, and portable explosive line charges. The 45-meter depth requires multiple uses of those assets.

Antitank Mines

The minefield focuses on the dismounted threat. Normally, AT mines are useful only if the enemy has vehicles.

Antipersonnel Mines

The M16A1 AP mine provides the best mix of lethality and density for the disrupt or fix minefield. The M18 Claymore mine is another choice. The M14 AP can be used; however, it requires a much higher linear density.

Antihandling Devices

The emplacing unit determines the requirement for AHDs based on the threat. At least some mines, especially those on the leading edge of the minefield, should have AHDs.

Irregular Outer Edges

The IOE's purpose is to confuse the enemy about the orientation of the minefield and to increase the enemy's probability of encounter. Use of the IOE is normal only in relatively open terrain.

Leaders should not limit their view of reinforcing obstacles only to minefields.

Note that throughout this manual, individual obstacles are depicted as shaded rectangles unless a specific variety of obstacle is discussed. Those shaded rectangles represent individual obstacles. The actual type of individual obstacle depends on METT-T. Leaders should consider the full range of individual obstacle varieties when installing individual obstacles. Leaders have as many options as their imaginations allow.


The standard row minefields in FM 20-32 are classified as disrupt, fix, turn, and block. Although these minefields are classified that way, the array of individual obstacles is what supports the obstacle effect. Units may use any of these minefields or other obstacles to achieve an obstacle effect if the array supports the desired effect. Figure A-5 shows possible obstacle arrays to support specific effects.

It also is important to fit standard obstacles to the terrain. For example, units do not need to lay row minefields in a straight line. They must array the obstacle based on the weapon systems and the terrain to achieve a specific effect. Figures A-6, A-7, and A-8, show some examples of how to use standard obstacles in different arrays to achieve an obstacle effect.

Standard obstacles enable planners at all echelons to estimate resource requirements based on linear obstacle requirements. Like all planning factors, they provide a base for estimating requirements and must be adjusted to the factors of METT-T. Production rates decrease because of limited visibility; nuclear, biological, and chemical (NBC) threat environment; reduced troop strength or proficiency; and adverse weather conditions.

Figure A-5. Possible array of obstacles.

Figure A-6. Standard obstacle in open terrain.

Figure A-7. Standard obstacles on a narrow mobility corridor.

Figure A-8. Standard obstacles in restrictive terrain.

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