Infantry Drills

FM 3-21.8 – Chapter 8 – Section V – Occupation and Preparation of Defensive Positions

Section V – Occupation and Preparation of Defensive Positions

8-77.     Occupation and preparation of defensive positions is conducted concurrently with the TLP and engagement area development. The process is not sequential. The potential problem associated with this process is the lack of adequate preparation time if the platoon has several other defensive positions (alternate, supplementary, and subsequent) and engagement areas to develop.


8-78.     The platoon occupies defensive positions IAW the platoon leader’s plan and the results of the reconnaissance.

8-79.     To ensure an effective and efficient occupation, rifle squads move to the locations marked previously by the reconnaissance element. These positions may also be on the operational graphics. Once in position, each squad leader checks his location on the map to ensure he is complying with the platoon leader’s graphics. As the platoon occupies its positions, the platoon leader ensures that each squad locates IAW his plan. If the platoon leader notes discrepancies between actual positioning of the squads and his plan, he corrects it immediately.

8-80.     Once each rifle squad has occupied its position, the platoon leader must walk the positions to ensure that weapons orientation, positioning of the rifle squads, and understanding of the plan are IAW the pre-established plan. The platoon leader should not rely on updates from his subordinates. He should always walk his defensive perimeter. For command and control purposes, each squad leader must know the location of the platoon leader and the platoon sergeant.

8-81.     Night vision equipment enhances the occupation process under limited visibility conditions. For instance, the platoon leader can mark his position with an infrared light source and squad leaders can move to premarked positions with infrared light sources showing them where to locate. Additionally, the squad leaders can use AN/PAQ-4B/Cs or AN/PEQ-2As to point out sectors of fire and TRPs to their Soldiers, using infrared light sources to keep the occupation clandestine.

8-82.     The platoon may conduct a hasty occupation in the defense during a counterattack or after disengagement and movement to alternate, supplementary, or subsequent defensive positions.

8-83.     The platoon leader issues a FRAGO covering the following minimum information:

– Changes in the enemy or friendly situation.

– The platoon task and purpose (what the platoon must accomplish and why).

– The task and purpose for each subordinate element.

– The scheme of fires.

– Coordinating instructions.

8-84.     At a minimum, the following actions must be taken:

– The platoon approaches the defensive positions from the rear or flank.

– The platoon establishes direct fire control measures or, if these are preplanned, reviews the plan.

– The platoon leader reports, “Occupied” to the company commander.

8-85.     The platoon conducts deliberate occupation of defensive positions when time is available, when enemy contact is not expected, and when friendly elements are positioned forward in the sector to provide security for forces in the main battle area. Actually establishing defensive positions is accomplished concurrently with the development of the engagement area. The platoon leader directs the initial reconnaissance from the engagement area and then tentatively emplaces crew-served weapon systems.

8-86.     Once the defensive positions are established, subordinate leaders can begin to develop their sector sketches and fire plans based on the basic fire plan developed during the leader’s reconnaissance. Fighting positions are improved while the direct fire plan is finalized and proofed. The platoon leader, with guidance from the company commander, designates the level of preparation for each defensive position based on the time available and other tactical considerations for the mission. The three levels of defensive position preparation (occupy, prepare, and reconnoiter) are listed here in descending order of thoroughness and time required.


8-87.     Complete the preparation of the position from where the platoon will initially defend. The position is fully reconnoitered, prepared, and occupied prior to the “defend not later than (NLT)” time specified in the company order. The platoon must rehearse the occupation, and the platoon leader must establish a trigger for occupation of the position.


8-88.     The position and the corresponding engagement area will be fully reconnoitered. Squad positions in the defensive positions and direct fire control measures in the engagement area should be marked. Survivability positions may be dug, ammunition caches pre-positioned, and protective obstacles emplaced.


8-89.     Both the engagement area and defensive positions will be fully reconnoitered. Tentative weapon positions should be planned in the defensive positions, and direct fire control measures should be established in the engagement area.

8-90.     In addition to establishing the platoon’s primary defensive positions, the platoon leader and subordinate leaders normally plan for preparation and occupation of alternate, supplementary, and subsequent defensive positions. This is done IAW the company order. See Section II for characteristics of alternate, supplementary, and subsequent defensive positions.


8-91.     Leaders must ensure that Soldiers prepare for the defense quickly and efficiently. Work must be done in order of priority to accomplish the most in the least amount of time while maintaining security and the ability to respond to enemy action. Below are basic considerations for priorities of work.

– Emplace local security (all leaders).

– Position and assign sectors of fire for each squad (platoon leader).

– Position and assign sectors of fire for the CCMS and medium machine gun teams (platoon leader).

– Position and assign sectors of fire for M249 MG, grenadiers, and riflemen (squad leaders).

– Establish command post and wire communications.

– Designate FPLs and FPFs.

– Clear fields of fire and prepare range cards.

– Prepare sector sketches (leaders).

– Dig fighting positions (stage 1 [see Section VII]).

– Establish communication and coordination with the company and adjacent units.

– Coordinate with adjacent units. Review sector sketches.

– Emplace antitank and Claymore mines, then wire and other obstacles.

– Mark or improve marking for TRPs and other fire control measures.

– Improve primary fighting positions and add overhead cover (stage 2).

– Prepare supplementary and then alternate positions (same procedure as the primary position).

– Establish sleep and rest plans.

– Distribute and stockpile ammunition, food, and water.

– Dig trenches to connect positions.

– Continue to improve positions—construct revetments, replace camouflage, and add to overhead cover.

8-92.     Unit priorities of work are normally found in SOPs. However, the commander will dictate the priorities of work for the company based on the factors of METT-TC. Several actions may be accomplished at the same time. Leaders must constantly supervise the preparation of fighting positions, both for tactical usefulness and proper construction.


8-93.     Security in the defense includes all active and passive measures taken to avoid detection by the enemy, deceive the enemy, and deny enemy reconnaissance elements accurate information on friendly positions. The two primary tools available to the platoon leader are observation posts and patrols. In planning for the security in the defense, the platoon leader considers the terrain in terms of OAKOC. He uses his map to identify terrain that will protect the platoon from enemy observation and fires while providing observation and fires into the engagement area. Additionally, he uses intelligence updates to increase his situational understanding, reducing the possibility of the enemy striking at a time or in a place for which the platoon is unprepared.

Observation Posts

8-94.     An observation post gives the platoon its first echelon of security in the defense. The observation post provides early warning of impending enemy contact by reporting direction, distance, and size. It detects the enemy early and sends accurate reports to the platoon. The platoon leader establishes observation posts along the most likely enemy avenues of approach into the position or into the area of operations. Leaders ensure that observation posts have communication with the platoon.

8-95.     Early detection reduces the risk of the enemy overrunning the observation post. Observation posts may also be equipped with a Javelin CLU to increase the ability to detect the enemy. They may receive infrared trip flares, infrared parachute flares, infrared M203 rounds, and even infrared mortar round support to illuminate the enemy. The platoon leader weighs the advantages and disadvantages of using infrared illumination when the enemy is known to have night vision devices that detect infrared light. Although infrared and thermal equipment within the platoon enables the platoon to see the observation post at a greater distance, the observation post should not be positioned outside the range of the platoon’s small-arms weapons.

8-96.     To further reduce the risk of fratricide, observation posts use GPS, if available, to navigate to the exit and entry point in the platoon’s position. The platoon leader submits an observation post location to the company commander to ensure a no-fire area (NFA) is established around each observation post position. The commander sends his operational overlay with observation post positions to the battalion and adjacent units. He receives the same type overlay from adjacent units to assist in better command and control and fratricide avoidance. The platoon leader confirms that the company fire support element (FSE) has forwarded these locations to the battalion FSO and has received the appropriate NFAs on the fire support graphics.


8-97.     Platoons actively patrol in the defense. Patrols enhance the platoon’s ability to fill gaps in security between observation posts (see Chapter 9). The platoon leader forwards his tentative patrol route to the commander to ensure they do not conflict with other elements within the company. The commander forwards the entire company’s patrol routes to the battalion. This allows the battalion S3 and S2 to ensure all routes are coordinated for fratricide prevention, and that the company and platoons are conforming to the battalion intelligence, surveillance, and reconnaissance (ISR) plan. The patrol leader may use a GPS to enhance his basic land navigational skills as he tracks his patrol’s location on a map, compass, and pace count or odometer reading.


8-98.     Platoons establish defensive positions IAW the platoon leader and commander’s plan. They mark engagement areas using marking techniques prescribed by unit SOP. The platoon physically marks obstacles, TRPs, targets, and trigger lines in the engagement area. During limited visibility, the platoon can use infrared light sources to mark TRPs for the rifle squads. When possible, platoons should mark TRPs with both a thermal and an infrared source so the rifle squads can use the TRP.

Range Card

8-99.     A range card is a sketch of a sector that a direct fire weapons system is assigned to cover. Range cards aid in planning and controlling fires. They also assist crews in acquiring targets during limited visibility, and orient replacement personnel, platoons, or squads that are moving into position. During good visibility, the gunner should have no problems maintaining orientation in his sector. During poor visibility, he may not be able to detect lateral limits. If the gunner becomes disoriented and cannot find or locate reference points or sector limit markers, he can use the range card to locate the limits. The gunner should make the range card so he becomes more familiar with the terrain in his sector. He should continually assess the sector and, if necessary, update his range card.

Sector Sketches

8-100.  Detailed sketches aid in the planning, distribution, and control of the platoon fires. Gunners prepare the range cards. Squad leaders prepare squad sector sketches, section leaders prepare section sketches, and the platoon leader prepares the platoon sketch.


8-101.  To position weapons effectively, leaders must know the characteristics, capabilities, and limitations of the weapons; the effects of terrain; and the tactics used by the enemy. Additionally, the platoon leader must consider whether his primary threat will be vehicles or Infantry. His plan should address both mounted and dismounted threats. Also, the platoon leader may have an antitank section attached.

Close combat missile systems Employment

8-102.  The primary role of Close Combat Missile Systems (CCMS) is to destroy enemy armored vehicles. When there is no armored vehicle enemy, CCMS can be employed in a secondary role of providing fire support against point targets such as crew-served weapons positions. CCMS optics (such as the Javelin’s command launch unit [CLU]) can be used alone or as an aided vision device for reconnaissance, security operations, and surveillance. Reduced or limited visibility will not degrade the effectiveness of the CCMS. This fact allows the antiarmor specialist to continue to cover his sector without having to reposition closer to the avenue of approach. The platoon leader’s assessment of the factors of METT-TC will determine the employment of CCMS. (For a detailed discussion on the employment of the Javelin, refer to Appendix B.) Based on the situation, the platoon leader may employ all or some of the CCMS. He may use centralized control or decentralized control.

Centralized Control

8-103.  The platoon leader controls the fires of his CCMS gunners by both physically locating the weapons in his vicinity and personally directing their fires, or by grouping them together under the control of the platoon sergeant or weapons squad leader.

Decentralized Control

8-104.  CCMS gunners operate with and are controlled by their weapons squad leader. A rifle squad leader may need to employ one fire team with a CCMS. The platoon leader normally gives the command to fire.

Medium Machine Gun Employment

8-105.  Medium machine guns are the platoon’s primary crew-served weapons that are positioned first if the enemy is a dismounted force. (For a detailed discussion on the employment of the M240B and the M249, refer to Appendix A.) Once these guns are sited, the leader positions riflemen to protect them. The guns are positioned to place direct fire on locations where the platoon leader wants to concentrate combat power to destroy the enemy.

M203 Employment

8-106.  The M203 grenade launcher is the squad leader’s indirect fire weapon. The platoon leader positions the grenadier to cover dead space in the squad’s sector, especially the dead space for the medium machine guns. The grenadier is also assigned a sector of fire overlapping the riflemen’s sectors of fire. The high-explosive dual purpose (HEDP) round is effective against lightly armored vehicles.

Employment of Riflemen

8-107.  The platoon and squad leaders assign positions and sectors of fire to each rifleman in the platoon. Normally, they position the riflemen to support and protect machine guns and antiarmor weapons. Riflemen are also positioned to cover obstacles, provide security, cover gaps between platoons and companies, or provide observation.


8-108.  Coordination is important in every operation. In the defense, coordination ensures that units provide mutual support and interlocking fires. In most circumstances, the platoon leader conducts face-to-face coordination to facilitate understanding and resolve issues effectively. The platoon leader should send and receive the following information prior to conducting face-to-face coordination:

– Location of leaders.

– Location of fighting positions.

– Location of observation posts and withdrawal routes.

– Location and types of obstacles, including Claymores.

– Location, activities, and passage plan for reconnaissance platoon and other units forward of the platoon’s position.

– Location of all Soldiers and units operating in and around the platoon’s area of operations.

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