Infantry Drills

FM 3-21.8 – Chapter 2 – Section III – Engaging the Enemy without Endangering Friendly Troops

Section III – Engaging the Enemy without Endangering Friendly Troops

2-46.     In the offense, effective friendly supporting fires require firing on enemy targets that are close to assaulting friendly Infantry Soldiers. A safe integration of fires and maneuver this close demands careful planning, coordination, and knowledge of the supporting weapons. In the defense, the most common close support is the final protective fire (FPF), which is normally placed very close to friendly positions. When planning close supporting fires for the offense or defense, leaders consider the effect required, accuracy of the delivery system, protection of Soldiers, integration of assets, timings and control, echelonment of fires, and tactical risk from enemy forces.

2-47.     Munition effects do not distinguish between friendly forces, noncombatants, and the enemy. To inflict maximum casualties on the enemy while minimizing effects to friendly Soldiers and noncombatants, leaders must have an understanding of weapon-munition effects, SDZ, minimum safe distances (MSD), risk estimate distances (RED), and the terrain’s influence on projectiles. Failure to account for characteristics of direct and indirect weapon systems when considering tactics, techniques, and procedures can result in serious unintended consequences.

2-48.     There are many variables that impact on the accuracy of the weapon. Artillery and mortars are referred to as area weapon systems because every round fired from the same tube impacts in an area around target aiming point. This dispersion is greater in length than in width. The weather conditions (wind, temperature, and humidity), the condition of the weapon, and the proficiency of the crew also affect accuracy.

Surface Danger Zone

2-49.     The SDZ is the ground and airspace for vertical and lateral containment of projectiles, fragments, debris, and components resulting from the firing, launching, or detonation of weapon systems (including explosives and demolitions). Each weapon system or munition has its own unique SDZ. The critical components of the SDZ are the primary danger area and the buffer zone.

2-50.     Understanding the components of the SDZ enable leaders and their Soldiers to make good decisions concerning how close they can get to the effects of friendly weapon fire. SDZs are developed using precise technical data without considering the effects of terrain. This data should be consulted whenever exact specifications are required. However, because the technical data can be confusing, it is useful to describe SDZs in a general manner. For exact weapon SDZs (see DA Pam 385-63, Range Safety).

2-51.     The primary danger area consists of the dispersion and ricochet area along the gun-target line for the maximum range of the weapon. The dispersion area is a 5-degree angle to the right and left of the gun-target line that accounts for human error, gun or cannon tube wear, and propellant temperature. The ricochet area contains any projectiles that make contact with surrounding terrain following the munition’s initial impact.  It is located to the left and right of the dispersion area.  The buffer zone is an area outside of the ricochet area allocated for additional safety measures. The buffer area exists to the sides of the gun-target line and at the far end of the weapon’s maximum effect range.

Direct Fire

2-52.     For direct fire weapons, the risk of being hit by friendly munitions at the edge of the buffer zone is negligible. Based on the type of surface (earth, water, steel, or concrete), the risk increases significantly at the edge of the ricochet area. Risk is extremely high at the edge of the dispersion area. In accordance with DA PAM 385-63, the current level of acceptable risk in training is 1/1,000,000 (outside SDZ), but can be waived by the installation commander to 1/100,000 (outside ricochet area). In combat, most commanders use 1/100,000 (outside ricochet area) based upon METT-TC analysis and risk mitigation measures. Table 2-2 shows the probability of direct fire ricochets.


Table 2-2. Probability of ricochet.

Outside of Area Probability
SDZ (Area A) 1/1,000,000
Ricochet area 1/100,000
Dispersion area 1/10,000


2-53.     When Soldiers remain outside of the buffer zone, the probability of being hit by their own munitions is unlikely. This is true for training and combat. During training, units usually are not authorized to come any closer to the gun-target line than the buffer zone. However, there are many situations in combat that require Soldiers to get closer to the gun-target line of their supporting weapons than the buffer zone allows. In these situations, the leader must understand how to manage the risk to his unit. When assessing this risk the question for leaders to consider is: “Is the threat from the effects of my munitions greater than the threat from the enemy?”

Reducing Risk

2-54.      Given the uncertainty associated with combat and the threat of enemy action, leaders must understand how to reduce risks associated with fire and movement in proximity to direct and indirect fires. As a general rule, the dispersion and ricochet areas present an immediate danger to Soldiers. Observers and protective measures are therefore required.

2-55.     The easiest way to protect friendly forces from unintended consequences of their own weapons is to always have an observer. Skilled observers can see the impact of the rounds and any maneuver elements near that area. In circumstances where assigning observers is not possible, leaders must take other measures to mitigate the risk of unintended consequences to friendly forces. Some of the most common include:

– Wearing and requiring Soldiers to wear protective equipment (body armor, Kevlar helmet, eye protection, hearing protection).

– Using terrain, natural or man-made, to mask effects of munitions.

– Adding a buffer zone of additional distance to the gun-target line.

– Using armored vehicles.

– Using graphic control measures.

– Ensuring a highly qualified Soldier is operating the weapons system.

Minimum Safe Distance and Risk Estimate Distance

2-56.     When determining risk with indirect fires, leaders use a combination of minimum safe distances (MSDs), and risk estimated distances (REDs). The MSD risk is designed for training and ensures that friendly Soldiers are far enough away from the effects of munitions so the risk to them is negligible. REDs refer to a safe distance away from a given type of friendly munitions and are only used in combat. REDs are divided into two categories based on the percent of incapacitation (PI) to friendly Soldiers, expressed as .1 PI and 10 PI. The former (.1 PI) means that one in one thousand Soldiers will not be able to fight because of potential weapon munitions effects. The latter (10 PI) means that one in ten Soldiers will not be able to fight because of weapon effects. When MSDs and REDs are put together, the leader is able to manage his risk from negligible—to 10 PI—based on his distance from the impact of friendly supporting indirect fire. Table 2-3 contains a complete listing of MSDs and REDs for common fire support assets at maximum range of weapons systems. (At lesser ranges the RED decreases).


Table 2-3. MSDs and REDs for common fire support assets.

Weapon System MSD (Training)

RED (Combat)

.1 PI 10 PI
60-mm Mortar (M224) 250m 175m 65m
81-mm Mortar (M252) 350m 230m 80m
120-mm Mortar (M120/M121) 600m 400m 100m
105-mm Artillery (M102/M119) 550m 275m 90m
155-mm Artillery (M109/M198) 725m 450m 125m
155-mm Artillery DPICM 725m 475m 200m




REDs are for combat use and do not represent the maximum fragmentation envelopes of the weapons listed. REDs are not minimum safe distances for peacetime training use.


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