Infantry Drills

FM 3-21.8 – Chapter 7 – Section IX – Attacking Fortified Positions

Section IX – Attacking Fortified Positions

7-208.  Fortifications are works emplaced to defend and reinforce a position. Time permitting, enemy defenders build bunkers and trenches, emplace protective obstacles, and position mutually supporting fortifications when fortifying their positions. Soldiers who attack prepared positions should expect to encounter a range of planned enemy fires to include small arms fire, mortars, artillery, antitank missiles, antitank guns, tanks, attack aviation, and close air support. Attacking forces should also expect a range of offensive type maneuver options to include spoiling attacks, internal repositioning, counterattacks, and withdrawing to subsequent defensive positions. Spoiling attacks will attempt to disrupt the attacker’s momentum and possibly seize key terrain. If driven out of their prepared positions, enemy troops may try to win them back by hasty local counterattacks or through deliberate, planned combined arms counterattacks. If forced to withdraw, the enemy forces may use obstacles, ambushes, and other delaying tactics to slow down pursuing attackers.

7-209.  The attack of a fortified position follows the basic principles of tactical maneuver. However, greater emphasis is placed upon detailed planning, special training and rehearsals, increased fire support, and the use of special equipment. The degree of special preparation depends upon the character, and extent of the defense.

7-210.  The deliberate nature of defenses requires a deliberate approach to the attack. These types of operations are time consuming. Leaders must develop schemes of maneuver that systematically reduce the area. Initially, these attacks should be limited in scope, focusing on individual positions and intermediate terrain objectives. Leaders must establish clear bypass criteria and position destruction criteria as well as allocate forces to secure cleared enemy positions. Failure in this will likely result in enemy reoccupying the positions, isolating lead elements, and ambushing follow-on units.

7-211.  The intense, close combat prevalent in trench clearing is remarkably similar to fighting in built up areas. Comparable characteristics include:

– Restricted Observation and Fields of Fire. Once the trench is entered, visibilities may be limited to a few meters in either direction. This compartmentalization necessarily decentralizes the engagement to the lowest level.

– Cover and Concealment. The nature of a trench system allows covered movement of both friendly and enemy forces. To prevent being flanked or counterattacked, junctions, possible entry points, and corners should be secured.

– Difficulty in Locating the Enemy. The assault element may come under fire from multiple mutually supporting positions in the trench or a nearby position. The exact location of the fire may be difficult to determine. Supporting elements outside the trench should be capable of locating, suppressing, or destroying such threats.

– Close Quarters Fighting. Because of the close nature of the trench system, Soldiers should be prepared to use close quarters marksmanship, bayonet, and hand-to-hand fight techniques.

– Restricted Movement. Trench width and height will severely restrict movement inside the system. This will ordinarily require the assault element to move at a low crouch or even a crawl. Sustainment functions such as ammunition resupply, EPW evacuation, casualty evacuation, and reinforcement will also be hampered.

– Sustainment. The intensity of close combat in the trench undoubtedly results in increased resource requirements.


7-212.  Finding the enemy’s fortified positions relates back to the position’s purpose. There are two general reasons to create fortified positions. The first includes defending key terrain and using the position as a base camp, shelter, or sanctuary for critical personnel or activities. This type of position is typically camouflaged and difficult to locate. When U.S. forces have air superiority and robust reconnaissance abilities, enemy forces will go to great lengths to conceal these positions. Sometimes the only way to find these enemy positions is by movement to contact. When Infantry platoons or squads encounter a previously unidentified prepared enemy position, they should not, as a general rule, conduct a hasty attack until they have set conditions for success.

7-213.   The second general purpose for fortified positions is to create a situation in which the attacker is required to mass and present a profitable target. This type of position normally occurs in more conventional battles. These positions can be relatively easy to find because they occupy key terrain, establish identifiable patterns, and generally lack mobility.

7-214.  Attacking fortified positions requires thorough planning and preparation based on extensive reconnaissance.


7-215.  An enemy in fortified defenses has already partially fixed himself. This does not mean he will not be able to maneuver or that the fight will be easy. It does mean that the objective is probably more defined than with an enemy with complete freedom of movement. Fixing the enemy will still require measures to prevent repositioning to alternate, supplementary, and subsequent positions on the objective and measures to block enemy counterattack elements.

Finishing an enemy in prepared positions requires the attacker to follow the fundamentals of the offense-surprise, concentration, tempo, and audacity to be successful.


7-217.  The actual fighting of enemy fortifications is clearly an Infantry platoon unit function because squads and platoons, particularly when augmented with engineers, are the best organized and equipped units in the Army for breaching protective obstacles. They are also best prepared to assault prepared positions such as bunkers and trench lines. Infantry platoons are capable of conducting these skills with organic, supplementary, and supporting weapons in any environment.

7-218.  Leaders develop detailed plans for each fortification, using the SOSRA technique to integrate and synchronize fire support and maneuver assets. Although there are specific drills associated with the types of fortifications, the assault of a fortified area is an operation, not a drill. During planning, the leader’s level of detail should identify each aperture (opening or firing port) of his assigned fortification(s) and consider assigning these as a specific target when planning fires. Contingency plans are made for the possibility of encountering previously undetected fortifications along the route to the objective, and for neutralizing underground defenses when encountered.

Securing the Near and Far Side—Breaching Protective Obstacles

7-219.  To fight the enemy almost always requires penetrating extensive protective obstacles, both antipersonnel and antivehicle. Of particular concern to the Infantrymen are antipersonnel obstacles. Antipersonnel obstacles (both explosive and nonexplosive) include, wire entanglements; trip flares; antipersonnel mines; field expedient devices (booby traps, nonexplosive traps, punji sticks); flame devices; rubble; warning devices; CBRN; and any other type of obstacle created to prevent troops from entering a position. Antipersonnel obstacles are usually integrated with enemy fires close enough to the fortification for adequate enemy surveillance by day or night, but beyond effective hand grenade range. Obstacles are also used within the enemy position to compartmentalize the area in the event outer protective barriers are breached. See Appendix F for more information on obstacles.

7-220.  The following steps are an example platoon breach:

– The squad leader and the breaching fire team move to the last covered and concealed position near the breach point (point of penetration).

– The squad leader confirms the breach point.

– The platoon leader or squad leader shifts the suppressing element away from the entry point.

– The fire element continues to suppress enemy positions as required.

– Buddy team #1 (team leader and the automatic rifleman) remains in a position short of the obstacle to provide local security for buddy team #2.

– The squad leader and breaching fire team leader employ smoke grenades to obscure the breach point.

– Buddy team #2 (grenadier and rifleman) moves to the breach point. They move in rushes or by crawling.

– The squad leader positions himself where he can best control his teams.

– Buddy team #2 positions themselves to the right and left of the breach point near the protective obstacle.

– Buddy team #2 probes for mines and creates a breach, marking their path as they proceed.

– Once breached, buddy team #1 and buddy team #2 move to the far side of the obstacle and take up covered and concealed positions to block any enemy movement toward the breach point. They engage all identified or likely enemy positions.

– The squad leader remains at the entry point and marks it. He calls forward the next fire team with, “Next team in.”

– Once the squad has secured a foothold, the squad leader reports to the platoon leader, “Foothold secure.” The platoon follows the success of the seizure of the foothold with the remainder of the platoon.

Knocking Out Bunkers

7-221.  The term bunker in this FM covers all emplacements having overhead cover and containing apertures (embrasures) through which weapons are fired. The two primary types are reinforced concrete pillboxes, and log bunkers. There are two notable exploitable weaknesses of bunkers.

7-222.  First, bunkers are permanent, their location and orientation fixed. Bunkers cannot be relocated or adjusted to meet a changing situation. They are optimized for a particular direction and function. The worst thing an Infantry platoon or squad can do is to approach the position in the manner it was designed to fight. Instead, the unit should approach the position from the direction it is least able to defend against—the flank or rear.

7-223.  Second, bunkers must have openings (doors, windows, apertures, or air vents). There are two disadvantages to be exploited here. First, structurally, the opening is the weakest part of the position and will be the first part of the structure to collapse if engaged. Second, a single opening can only cover a finite sector, creating blind spots. To cover these blind spots, the defender has to either rely on mutually supporting positions or build an additional opening. Mutual support may be disrupted, thereby enabling the attacker to exploit the blind spot. Adding additional openings correspondingly weakens the position’s structural soundness, in which case the attacker targets the opening to collapse the position.

7-224.  Ideally the team is able to destroy the bunker with standoff weapons and HE munitions. However, when required, the fire team can assault the bunker with small arms and grenades. A fire team (two to four men) with HE and smoke grenades move forward under cover of the suppression and obscuration fires from the squad and other elements of the base of fire. When they reach a vulnerable point of the bunker, they destroy it or personnel inside with grenades or other hand-held demolitions. All unsecured bunkers must be treated as if they contain live enemy, even if no activity has been detected from them. The clearing of bunkers must be systematic or the enemy will come up behind assault groups. To clear a bunker—

– The squad leader and the assault fire team move to the last covered and concealed position near the position’s vulnerable point.

– The squad leader confirms the vulnerable point

– The platoon leader/squad leader shifts the base of fire away from the vulnerable point.

– The base of fire continues to suppress the position and adjacent enemy positions as required.

– Buddy team #1 (team leader and the automatic rifleman) remain in a position short of the position to add suppressive fires for buddy team #2 (grenadier and rifleman).

– Buddy team #2 moves to the vulnerable point. They move in rushes or by crawling.

– One Soldier takes up a covered position near the exit.

– The other Soldier cooks off a grenade (2 seconds maximum), shouts, FRAG OUT, and throws it through an aperture.

– After the grenade detonates, the Soldier covering the exit enters and clears the bunker.

– Simultaneously, the second Soldier moves into the bunker to assist Soldier #1.

– Both Soldiers halt at a point of domination and take up positions to block any enemy movement toward their position.

– Buddy team #1 moves to join buddy team #2.

– The team leader inspects the bunker, marks the bunker, and signals the squad leader.

– The assault squad leader consolidates, reorganizes, and prepares to continue the mission.

Assaulting Trench Systems

7-225.  Trenches are dug to connect fighting positions. They are typically dug in a zigzagged fashion to prevent the attacker from firing down a long section if he gets into the trench, and to reduce the effectiveness of high explosive munitions. Trenches may also have shallow turns, intersections with other trenches, firing ports, overhead cover, and bunkers. Bunkers will usually be oriented outside the trench, but may also have the ability to provide protective fire into the trench.

7-226.  The trench provides defenders with a route that has frontal cover, enabling them to reposition without the threat of low trajectory fires. However, unless overhead cover is built, trenches are subject to the effects of high trajectory munitions like the grenade, grenade launcher, plunging machine gun fire, mortars, and artillery. These types of weapon systems should be used to gain and maintain fire superiority on defenders in the trench.

7-227.  The trench is the enemy’s home, so there is no easy way to clear it. Their confined nature, extensive enemy preparations, and the limited ability to integrate combined arms fires makes trench clearing hazardous for even the best trained Infantry. If possible, a bulldozer or plow tank can be used to fill in the trench and bury the defenders. However, since this is not always feasible, Infantry units must move in and clear trenches. Although obscuration is necessarily outside the trench, it can be more of hindrance to the attacker inside the trench. Use of night vision equipment also requires special considerations.

Entering the Trenchline

7-228.  To enter the enemy trench the platoon takes the following steps:

– The squad leader and the assault fire team move to the last covered and concealed position near the entry point.

– The squad leader confirms the entry point.

– The platoon leader or squad leader shifts the base of fire away from the entry point.

– The base of fire continues to suppress trench and adjacent enemy positions as required.

– Buddy team #1 (team leader and automatic rifleman) remains in a position short of the trench to add suppressive fires for the initial entry.

– Buddy team #2 (grenadier and rifleman) and squad leader move to the entry point. They move in rushes or by crawling (squad leader positions himself where he can best control his teams).

– Buddy team #2 positions itself parallel to the edge of the trench. Team members get on their backs.

– On the squad leader command of COOK OFF GRENADES (2 seconds maximum), they shout, FRAG OUT, and throw the grenades into the trench.

– Upon detonation of both grenades, the Soldiers roll into the trench, landing on their feet and back-to-back. They engage all known, likely or suspected enemy positions.

– Both Soldiers immediately move in opposite directions down the trench, continuing until they reach the first corner or intersection.

– Both Soldiers halt and take up positions to block any enemy movement toward the entry point.

– Simultaneously, buddy team #1 moves to and enters the trench, joining buddy team #2. The squad leader directs them to one of the secured corners or intersections to relieve the Soldier who then rejoins his buddy at the opposite end of the foothold.

– At the same time, the squad leader rolls into the trench and secures the entry point.

– The squad leader remains at the entry point and marks it. He calls forward the next fire team with, NEXT TEAM IN.

– Once the squad has secured a foothold, the squad leader reports to the platoon leader, FOOTHOLD SECURE. The platoon follows the success of the seizure of the foothold with the remainder of the platoon.

7-229.  The leader or a designated subordinate must move into the trench as soon as possible to control the tempo, specifically the movement of the lead assault element and the movement of follow-on forces. He must resist the temptation to move the entire unit into the trench as this will unduly concentrate the unit in a small area. Instead,, he should ensure the outside of the trench remains isolated as he maintains fire superiority inside the trench. This may require a more deliberate approach. When subordinates have reached their objectives or have exhausted their resources, the leader commits follow-on forces or requests support from higher. Once stopped, the leader consolidates and reorganizes.

7-230.  The assault element is organized into a series of three-man teams. The team members are simply referred to as number 1 man, number 2 man, and number 3 man. Each team is armed with at least one M249 and one grenade launcher. All men are armed with multiple hand grenades.

7-231.  The positioning within the three-man team is rotational, so the men in the team must be rehearsed in each position. The number 1 man is responsible for assaulting down the trench using well aimed effective fire and throwing grenades around pivot points in the trenchline or into weapons emplacements. The number 2 man follows the number 1 man closely enough to support him but not so closely that both would be suppressed if the enemy gained local fire superiority. The number 3 man follows the number 2 man and prepares to move forward when positions rotate.

7-232.  While the initial three-man assault team rotates by event, the squad leader directs the rotation of the three-man teams within the squad as ammunition becomes low in the leading team, casualties occur, or as the situation dictates. Since this three-man drill is standardized, three-man teams may be reconstituted as needed from the remaining members of the squad. The platoon leader controls the rotation between squads using the same considerations as the squad leaders.

Clearing the Trenchline

7-233.  Once the squad has secured the entry point and expanded it to accommodate the squad, the rest of the platoon enters and begins to clear the designated section of the enemy position. The platoon may be tasked to clear in two directions if the objective is small. Otherwise, it will only clear in one direction as another platoon enters alongside and clears in the opposite direction.

7-234.  The lead three-man team of the initial assault squad moves out past the security of the support element and executes the trench clearing drill. The number 1 man, followed by number 2 man and number 3 man, maintains his advance until arriving at a pivot, junction point, or weapons emplacement in the trench. He alerts the rest of the team by yelling out, POSITION or, JUNCTION, and begins to prepare a grenade. The number 2 man immediately moves forward near the lead man and takes up the fire to cover until the grenade can be thrown around the corner of the pivot point. The number 3 man moves forward to the point previously occupied by number 2 and prepares for commitment.

7-235.  If the lead man encounters a junction in the trench, the platoon leader should move forward, make a quick estimate, and indicate the direction the team should continue to clear. This will normally be toward the bulk of the fortification or toward command post emplacements. He should place a marker (normally specified in the unit TSOP) pointing toward the direction of the cleared path. After employing a grenade, the number 2 man moves out in the direction indicated by the platoon leader and assumes the duties of the number 1 man. Anytime the number 1 man runs out of ammunition, he shouts, MAGAZINE, and immediately moves against the wall of the trench to allow the number 2 man to take up the fire. Squad leaders continue to push uncommitted three-man teams forward, securing bypassed trenches and rotating fresh teams to the front.  It is important to note that trenches are cleared in sequence not simultaneously.

Moving in a Trench

7-236.  Once inside, the trench teams use variations of the combat formations described in Chapter 3 to move. These formations are used as appropriate inside buildings as well. The terms hallway and trench are used interchangeably. The column (file) and box formations are self explanatory. The line and echelon formations are generally infeasible.

Follow-t Sis area and the surrounding dispositions if time allows. This information will be helpful for the higher headquarters intelligence officer or if the unit occupies the position for an extended length of time.

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