Infantry Drills

FM 3-21.8 – Chapter 2 – Section II – Weapon and Munition Characteristics

Section II – Weapon and Munition Characteristics

2-23.     To better understand the science of employing fires, leaders should know the basic characteristics of weapons and munitions. This knowledge leads to an  increased understanding of capabilities and the ability to achieve complementary, reinforcing effects.

Common weapons and munition characteristics

2-24.     There are five types of weapons used at the Infantry platoon level: small arms; machine guns; grenade launchers; shoulder-launched munitions (SLM)/Close Combat Missile System (CCMS); and mortars. These weapons are developed with emphasis on certain characteristics (Table 2-1).

Table 2-1. Common weapon characteristics.

Small Arms

Machine Gun

Grenade Launcher



Lay Direct fire Direct fire Direct fire Direct fire Indirect fire
Ammunition Penetration Penetration HE Penetration/ HE HE



Trajectory Low trajectory Low trajectory High trajectory Low trajectory High


Point or Area Enemy Target Point target Point and area target Point and area target Point target Area target
Organic Infantry Unit Weapons M4


M249 MG

M240 MG

M203 AT4




Organic to company/ battalion


2-25.     The lay of a weapon is the characteristic that determines how a Soldier engages a target. A weapon’s lay is either direct or indirect fire. Every weapon organic to the Infantry platoon or squad is direct fire, with the exception of company and battalion mortars. Infantry Soldiers armed with organic weapons engage the enemy with the weapon’s own sight. The strength of a direct fire weapon is its responsiveness. The weapon does not need to be requested from higher, nor does higher have to “clear fires” before a round may be fired. Soldiers manning indirect fire weapons such as mortars engage the enemy by using a separate observer (Figure 2-2).  Soldiers manning mortar weapon systems have the tactical advantage of avoiding direct contact with the enemy in the fight.

Figure 2-2. Indirect fire.


2-26.     For the purpose of this manual, there are three categories of ammunition: high explosive (HE); penetration; and special purpose munitions. Only HE and penetration munitions are considered for achieving complementary and reinforcing effects. The leader is able to engage known enemy targets (those he can see and acquire) as well as likely enemy targets (those he cannot see and cannot clearly acquire). If the enemy remains hidden but suspected, the grenadier will engage him with high explosives. If the enemy attempts to move to a location that will protect him from HE munition, the automatic rifleman will engage him with a penetrating munition. Special purpose munitions are described for general information only.

High Explosive

2-27.     HE munitions are used to kill enemy soldiers, force enemy soldiers to remain under protective field fortification cover, force an enemy vehicle to button up, or force an enemy vehicle into a less advantageous position. Only a direct hit will destroy or significantly damage an armored vehicle.

2-28.     There are two noteworthy strengths of HE munitions. First, HE muntions do not have to score a direct hit to physically affect the target. This makes it possible to engage targets that are not clearly acquired, but are likely or suspected. Second, HE munitions are especially effective at destroying structures such as bunkers and vehicles.


2-29.     The effectiveness of penetration munitions is dependent on the weapon system’s ability to generate velocity, and the ability of the munition’s mass to punch a hole in the enemy target. It is fairly easy to gauge the effectiveness of penetration munitions. Soldiers can engage targets with confidence because of the known effect the round will have on a target. The three general categories of penetration munitions are ball and tracer, armor piercing, and high explosive antitank (HEAT).

Ball and Tracer

2-30.     Ball and tracer rounds use high velocity to penetrate soft targets on impact. Penetration depends directly on the projectile’s velocity, weight, and angle at which it hits. Ball and tracer rounds are usually  small caliber (5.56 to 14.5 millimeters) and are fired from pistols, rifles, and machine guns.

Armor Piercing

2-31.     Armor piercing rounds use shaped-charged or kinetic energy penetration warheads specially designed to penetrate armor plate and other types of homogeneous steel. They are used effectively against fuel supplies and storage areas.

HEAT (High Explosive Antitank)

2-32.     HEAT rounds are designed to defeat armor through the use of shaped charge. A shaped charge is an explosive charge created so the force of the explosion is focused in a particular direction.

Special Purpose

2-33.     There are many types of munitions that do not fit the profile of the two major categories (HE and penetration). These are called special purpose munitions. Examples are incendiary, obscuration, illumination, nuclear, and chemical rounds.


2-34.     Infantry Soldiers can more effectively engage moving enemy targets with low trajectory fire than high trajectory fire. Enemy reaction when engaged with friendly low trajectory fire is predictable: get down and seek frontal cover. When this happens, high trajectory fire can effectively engage enemy targets in fighting positions, holes, or deadspace where low trajectory fire cannot. Friendly high trajectory fire can also force the enemy to move out of the area and seek overhead cover, limiting their effectiveness.

2-35.     Leaders create a dilemma for the enemy by combining low and high trajectory weapons. If the enemy gets up from his position and attempts to move, the automatic rifleman will engage him. If the enemy decides to stay in his position behind frontal cover, the grenadier will engage him. Either option results in the friendly force engaging the enemy. This united effect of the automatic rifleman and grenadier outweighs the effect either would have if they engaged the enemy without the other.

Enemy Target Types

2-36.     Weapons and munitions are designed for employment against the two general types of enemy targets: point, and area. Apoint target is located in a specific spot with a single aim point (enemy soldier, vehicle, piece of equipment). An area target is spread over an area with multiple aim points (formation of enemy soldiers, an enemy trench line). Some weapon systems such as machine guns and grenade launchers can effectively engage both point and area targets.

Fire team Weapons

2-37.     The rate of fire is the number of rounds fired in a minute by a particular weapon system. The leader dictates the rate of fire for each weapon system under his control. There are two factors that contribute to leader decisions about rates of fire: achieving fire superiority; and ammunition constraints. For information on equipment in the weapons squad or other supporting weapons, see Appendix A and Appendix B.


2-38.     Rifleman and Infantry leaders are currently armed with the M4 rifle. The M4 rifle is a direct fire weapon that fires ball and tracer 5.56-mm ammunition. The rifleman’s primary role is to kill the enemy with precision fire. In this capacity, the rate of fire for the M4 rifle is not based on how fast the Soldier can pull the trigger. Rather, it is based on how fast the Soldier can accurately acquire and engage the enemy. The second role of the rifleman is to engage likely or suspected enemy targets with suppressive fire.

M249 Machine Gun

2-39.     The automatic rifleman is currently armed with an M249 machine gun. The M249 is a direct-fire, low trajectory weapon that is primarily used to fire ball tracer 5.56-mm ammunition linked at area targets. The M249 also has the ability to fire unlinked 5.56-mm ammunition in 30-round magazines, but reliability is greatly reduced. Firing with a magazine should be limited to emergency situations.

M240B Machine Gun

2-40.     Two medium machine guns (currently the M240B) and crews are found in the Infantry platoon’s weapons squad. Machine gunners are a self-contained support by fire element or with a rifle squad to provide long range, accurate, sustained fires against enemy Infantry, apertures in fortifications, buildings, and lightly-armored vehicles. Machine gunners also provide a high volume of short-range fire in self defense against aircraft. THE M240B fires 7.62-mm ammunition. Refer to Appendix A for further information on machine guns.

Grenade Launcher

2-41.     The grenadier is currently armed with the M203 40-mm grenade launcher. The M203 is a direct fire, high trajectory weapon that can be used for either point or area targets. The M203 fires several types of munitions including, HE, high explosive dual purpose (HEDP) (antipersonnel/antiarmor), riot control (CS), buckshot, and signaling. As with the rifleman, the grenadier’s rate of fire is based on how quickly he can accurately acquire and engage the enemy.

Shoulder-Launched Munitions

2-42.     Shoulder-launched munitions (SLM) are lightweight, self-contained, single-shot, disposable weapons that consist of unguided free flight, fin-stabilized, rocket-type cartridges packed in launchers. SLM provide the Soldier a direct fire capability to defeat enemy personnel within field fortifications, bunkers, caves, masonry structures, and lightly armored vehicles. Soldiers use SLM to engage enemy combatants at very close ranges—across the street or from one building to another. Likewise, SLM may be fired at long distances to suppress the enemy or kill him. Soldiers may employ the SLM as a member of a support-by-fire element to incapacitate enemy forces that threaten the friendly assault element. When the assault element clears a building, the leader may reposition the SLM gunner inside to engage a potential counterattack force. Refer to Appendix B for further information on SLM.

Complementary and reinforcing effects at the fire team level

2-43.     One of the leader’s primary duties is to control the distribution of his unit’s fires.  An Infantry team leader tasked to establish support by fire uses the principles of complementary and reinforcing effects to guide his unit’s actions. The goal of each weapon system combination is to create an effect that outweighs the effects that either weapon system would make acting alone. The primary combination team leaders strive to employ are the weapons systems of the automatic rifleman and the grenadier. This combination is the center around which the remainder of the fire team’s functions revolves.

The Rifleman

2-44.     The rifleman’s role when the grenadier and automatic rifleman combine their fires is to perform one of three functions:

– Reinforce the automatic rifleman. If necessary, the rifleman can replace the automatic rifleman for a short time.

– Fix another target while the automatic rifleman and grenadier destroy the target they are engaging.

– Provide security and observation.

The Team Leader

2-45.     In weapon employment, the team leader’s role is to maximize the complementary effects of the combination of the grenadier and automatic rifleman. He does this through using proper fire commands and control measures. The team leader’s second role is to assume the duties of the rifleman if necessary.

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