H-8: Constructed Obstacles - Infantry Drills

H-8. Units create constructed obstacles with manpower or equipment without the use of explosives. Examples of constructed obstacles include:

Ditches. Ditches across roads and trails are obstacles. Large ditches in open areas require engineer equipment.
Log hurdles. Log hurdles act as “speed bumps” on roads. They are installed easily and are most effective when used in conjunction with other obstacles.
Log cribs. A log crib is constructed of logs, dirt, and rocks. The logs are used to make rectangular or triangular cribs filled with dirt and rock.
- These are used to block narrow roads and defiles. Unless substantially built, log cribs will not stop tanks.
Log posts. Log posts embedded in the road and employed in-depth can stop tracked vehicles. If they are not high enough to be pushed out of the way, posts can cause a tracked vehicle to throw a track if it tries to climb over. If employed with wire and mines, they also can slow enemy Infantry.
Wire entanglements. Wire entanglements impede the movement of dismounted enemy Infantry, and in some cases, tracked and wheeled vehicles.
- Triple standard concertina is a common wire obstacle. However, there are other types, such as double apron, tanglefoot, and general-purpose barbed-tape obstacles.
- Figures H-2a through H-2c (pages H-5 through H-6) illustrate examples of wire and log obstacles. The materials used in constructing wire entanglements are relatively lightweight (compared to other obstacles) and inexpensive, considering the protection they afford.

Figure H-2a. Constructed wire and log obstacles

Figure H-2b. Constructed wire and log obstacles

Figure H-2c. Constructed wire and log obstacles

Next: H-9: Demolition Obstacles

Go Back To: U.S. Army FM 3-21.8: The Infantry Rifle Platoon and Squad