Infantry Drills

FM 3-21.8 – Chapter 3 – Section VII – Security

Section VII – Security

3-153.  Maintaining security is a constant theme of tactical movement. Effective security can prevent enemy surprise. Security therefore requires everyone to concentrate on the enemy. Though this seems simple enough, in practice, it is not. This means that leaders and their Soldiers must be proficient in the basics of tactical movement. Failure to attain proficiency diverts attention away from the enemy, thereby directly reducing the unit’s ability to fight.

3-154.  Platoons and squads enhance their own security during movement through the use of covered and concealed terrain; the use of the appropriate movement formation and technique; the actions taken to secure danger areas during crossing; the enforcement of noise, light, and radiotelephone discipline; and the use of proper individual camouflage techniques.

3-155.  During planning and preparation for movement, leaders analyze the enemy situation, determine known and likely enemy positions, and develop possible enemy courses of action. After first considering the enemy, leaders determine what security measures to emplace during tactical movement.


3-156.  Leaders have to decide whether they are going to move aggressively to make contact, or stealthily to avoid contact. Either way, the leader has to anticipate enemy contact throughout. If possible, leaders should avoid routes with obvious danger areas such as built-up areas, roads, trails, and known enemy positions. If these places cannot be avoided, risk management should be conducted to develop ways to reduce danger to the unit. If stealth is desired, the route should avoid contact with local inhabitants, built-up areas, and natural lines of drift.

3-157.  Movement techniques help the leader manage the amount of security his unit has during movement. Traveling is the least secure and used when contact is not likely. Traveling overwatch is used when contact is likely but not imminent. Bounding overwatch is used when contact is imminent. Leaders establish the probable line of deployment (PLD) to indicate where the transition from traveling overwatch to bounding overwatch should occur. When in contact with the enemy, the unit transitions from movement to maneuver (fire and movement) while the leader conducts actions on contact (Figure 3-35).


Figure 3-35. Movement to maneuver.


3-158.  When planning movements, the leader must consider how terrain affects security while simultaneously considering the other factors of METT-TC. Some missions may require the unit to move on other than covered and concealed routes. While leaders may not be able to prevent the unit’s detection, they can ensure that they move on the battlefield in a time and place for which the enemy is unprepared. Particularly when moving in the open, leaders must avoid predictability and continue to use terrain to their advantage.

Camouflage, noise, and light discipline

3-159.  Leaders must ensure that camouflage used by their Soldiers is appropriate to the terrain and season. Platoon SOPs specify elements of noise and light discipline.

3-160.  If Soldiers need more illumination than an image intensifier can provide in infrared mode during movement, they should use additional infrared light sources. The combination should provide the light needed with the least risk of enemy detection. When using infrared light, leaders must consider the enemy’s night vision and infrared capabilities. For instance, an enemy with night vision capability can send infrared light signals, and he can concentrate direct and indirect fire on a platoon that is using infrared light.

Security at Halts

3-161.  Units conducting tactical movement frequently make temporary halts. These halts range from brief to extended periods of time. For short halts, platoons use a cigar-shaped perimeter intended to protect the force while maintaining the ability to continue movement. When the platoon leader decides not to immediately resume tactical movement, he transitions the platoon to a perimeter defense. The perimeter defense is used for longer halts or during lulls in combat.

Cigar-Shaped Perimeter

3-162.  When the unit halts, if terrain permits, Soldiers should move off the route and face out to cover the same sectors of fire they were assigned while moving, allowing passage through the center of the formation. This results in a cigar-shaped perimeter. Actions by subordinate leaders and their Soldiers occur without an order from the leader. Soldiers are repositioned as necessary to take advantage of the best cover, concealment, and fields of fire.

Perimeter Defense

3-163.  When operating independently, the platoon uses a perimeter defense during extended halts, resupply, and issuing platoon orders or lulls in combat. Normally the unit first occupies a short halt formation. Then after conducting a leader’s reconnaissance of the position and establishing security, the unit moves into the perimeter defense.

Actions at Halts

3-164.  Table 3-7 lists the standard actions taken at halts.

Table 3-7. Actions at halts.

Soldier (or Vehicle) Actions*

Squad Leader (or Section Leader) Actions

Platoon Leader Actions

·   Moves to as much of a covered and concealed position as available.

·   Visually inspects and physically clears his immediate surroundings (a roughly 5-25m radius around his position).

·   Establishes a sector of fire for his assigned weapon (using 12 o’clock as the direction the Soldier is facing, the Soldier’s sector of fire ranges from 10 o’clock to 2 o’clock).

·   Determines his observation and field of fire. Identifies dead space in his field of fire.

·   Identifies obstacles and determines enemy avenues of approach (both mounted and dismounted).

·   Identifies the dominant ground in his immediate surroundings.

·   Coordinates his actions with the Soldiers (or vehicles) on his left and right.

(*These actions occur without leader prompting.)

·  Adjusts his perimeter.

§         If operating independently, the squad leader establishes 360-degree, three-dimensional security.

§         Attempts to find terrain that anchors his position.

§         If operating as part of a platoon, the squad leader arrays his teams to best fit into the platoon leader’s defensive scheme, based on the platoon leader’s guidance.

·  Visually inspects and physically clears (if required) the squad’s immediate surrounding (about 35m, the distance within hand grenade range).

·  Ensures his squad’s individual sectors of fire overlap with each other, creating a seamless perimeter with no gaps of fire coverage.

·  Identifies his dead space and adjusts his M203 grenadiers accordingly.

·  Identifies obstacles and the likely enemy avenue of approach (mounted and dismounted).

·  Identifies the dominant ground in his area of operation.

·  Coordinates responsibilities and sectors with the units on his left and right.

·   Adjusts his perimeter.

§         If operating independently, he establishes 360-degree, three-dimensional security.

§         If operating as part of another organization, he arrays his squads to best fit into the controlling commander’s defensive scheme.

§         Supervises the emplacement of the weapons squad’s weapon systems.

·   Dispatches an element (usually a fire team) to visually inspect and physically clear the platoon’s immediate surrounding (an area out to small arms range, roughly 100-300m depending on terrain).

·   Ensures his squads’ sectors of fire overlap with each other, creating a seamless perimeter with no gaps of fire coverage.

·   Identifies his dead space not covered and requests indirect fire support to overwatch dead space in the area of operation.

·   Identifies obstacles and the likely enemy avenue of approach (mounted and dismounted).

·   Identifies the dominant ground in his area of operation.

·   Coordinates with the units on his left and right.


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