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LESSON 3

SELF TEST

ANSWER KEY AND FEEDBACK

1.   What is the purpose of employing obstacles?

An obstacle is employed to stop, or divert enemy movement by means other than firepower.

2.   Give an example of a nontactical obstacle.

An obstacle used to protect an installation against infiltration or sabotage is classified as a nontactical obstacle.

3.   Which of the following is the more effective natural obstacle against tracked vehicles — an escarpment 1.6 meters high or a river 60 meters wide and 1.1 meters deep?

An escarpment 1.5 meters high is an effective obstacle for both vehicles and personnel. Slopes must be approximately a 60 percent incline to stop the movement of tanks unless trees, rocks, or unfavorable soil is on the slope. Rivers must be over 150 meters wide and over 1.5 meters deep and swamps 1 meter deep before they become a major obstacle.

4.   In what type of terrain does the punji pit serve most effectively as an obstacle?

Punjis are an antipersonnel obstacle and are effective in jungles where the movement of troops is limited to marching.

5.   When should trip flares be used with obstacles?

Wherever it is feasible to have an obstacle under direct observation, trip flares may be used as a warning device to indicate that the enemy has encountered the obstacle. This will alert the unit prepared to supply the firepower.

6.   What may be used with barbed wire to make it a more effective antipersonnel obstacle?

Caltrops are used with barbed wire to make a more effective antipersonnel obstacle. Caltrops are designed to cause injury by penetrating the footwear.

7.   Which type of ditch is the most effective as an obstacle when it is camouflaged with snow:

A trapezoidal ditch may be camouflaged with snow to make it resemble a standard trench (fig 3-6). The enemy vehicles that are able to cross a standard trench will fall through the camouflaged portion of the excavation and be entrapped.

8.   Where is the best location for a cratering charge intended to impede the advancement of enemy vehicles traveling on a road?

Demolition placed in a culvert under the road is the most satisfactory method for cratering roads. If a culvert is not available, a hole may be dug into the road and a charge placed at the bottom of it. Placing a charge on the road is unsatisfactory because it can be seen. A charge placed in vegetation will ordinarily be alongside the road, which is ineffectual unless the charge is extremely large or of an atomic demolition munitions (ADM) type.

9.   From where should the earth be obtained to fill crib roadblocks?

The earth used to fill crib obstacles should preferably be obtained by digging a shallow ditch in front of the obstacle.

10.   In what position should posts be placed to serve as an antivehicular obstacle?

Posts used as an antivehicular obstacle are buried 1.5 meters in the ground either at a slight angle toward the enemy or vertically, projecting between 75 and 120 cm above ground level.

11.   What type of tree is most effective as an abatis?

Bush-type trees with heavy branches and thick foliage should be use for abatis wherever possible because the branches reduce the momentum of the vehicle. The trees should be at least 6 meters high and 60 cm or more in diameter.

12.   What disadvantage do steel hedgehogs have as an obstacle?

Steel hedgehogs can easily be moved by the enemy; therefore, these obstacles must be kept under observation and covered by fire.

13.   Which concrete obstacle is most frequently cast in place?

Concrete cube obstacles are usually cast in place because of the weight involved and the simplicity of making the forms in which they are made.

14.   What is the procedure which makes a truck a more effective roadblock?

A truck used as a roadblock should be emplaced and have the wheels damaged or removed to prevent it from being pulled out easily.

15.   What will make dummy road obstacles more effective?

Antitank and antipersonnel mines should be placed between dummy road obstacles.

16.   In major amphibious assault operations, who is responsible for the removing of obstacles in boat lanes in 8 meters of water on ocean shorelines?

Beyond the depth of 3 fathoms (5.54 meters), the Navy minesweepers are responsible for clearing boat and shipping lanes.

17.   Where should beach obstacles cause the enemy to disembark?

Beach obstacles should force the enemy landing craft to unload at low tide several hundred meters seaward of the high water mark. This makes the enemy cross a wide expanse of obstacle-studded beach and be vulnerable to fire.

18.   What obstacle is placed from wading depth at high tide to wading depth at low tide?

Antiboat obstacles are emplaced from wading depth at low tide to wading at high tide.

19.   What obstacle may have a post driven through it for better anchorage?

Timber tetrahedron's are pinned and wired to a triangular frame which is weighted in place with rocks. The anchorage may be improved by driving a post through the obstacle and into the ground.

20.   The hedgehog, the log ramp, the rock pillar, and the rock wall are all obstacles. Which is an expedient under water obstacle?

The rock wall is an expedient type of underwater obstacle made of rock found in the area. The rock pillar and the log ramp require wood and other material to construct and secure which takes them out of the expedient category. The hedgehog is a prefabricated obstacle.

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