Infantry Drills

FM 3-21.8 – Chapter 1 – Section IV – Combinations

Section IV — Combinations

1-101.  The Army’s preferred method of fighting is combined arms. Combined arms warfare is based on the concept of strengths and weaknesses. All weapons, branches, and tactics have strengths and weaknesses, advantages, and disadvantages. Understanding this, leaders use the power of combinations to protect their weaknesses while using their strengths to create dilemmas for the enemy. There are two principles that guide leaders in fighting combined arms: complementary effects; and reinforcing effects. These two principles are separate and distinct, but are present in most situations.

Complementary Effects

1-102.  Leaders create complementary effects when they arrange elements with different characteristics together (Figure 1-8). Complementary effects enable leaders to protect friendly vulnerabilities or enhance effects on the enemy. For example, leaders can combine the effects of their direct fire weapons with those of mortars or artillery to produce an overall greater effect than if each were used separately. Combinations are created based on understanding the strengths and weaknesses of their weapons, the different branches and services, and tactical tasks.


Figure 1-8. Complementary effects.


1-103.  A dilemma is a situation in which the enemy is presented with two or more equally bad alternatives. A problem is a situation in which the enemy is presented with only one bad alternative. Creative combinations allow the leader to create a dilemma for the enemy. When presented with a dilemma, an enemy has two reactions. The first reaction is not knowing what to do as he attempts to decide between equally bad options. This effect is commonly termed “fixed.” When the enemy is fixed, the leader benefits from freedom of action. The second reaction is to simply choose one of the two equally bad options. Because the enemy’s choice is an option in which the friendly force has the upper hand, the leader is able to exploit the enemy’s decision.

1-104.  Taking a single-tracked approach can lead to poor or unsuccessful results. Relying on one weapon type, on a single unit type, or a single tactical function does not present the enemy with a dilemma. Without a complementary effect, the enemy is exposed to a problem that can be resolved with a likely solution. Even if applied in rapid succession (sequentially), the enemy only needs to escape the problem at hand. Without a second or third stressor to impair his ability to make good decisions, the enemy is able to react and stay in the fight.

Reinforcing Effects

1-105.  Leaders create reinforcing effects when they combine the effect of similar capabilities (Figure 1-9). An example is a team leader reinforcing the effects of his squad automatic weapon with the fires of his rifleman. Leaders do this by either employing the elements simultaneously or sequentially to achieve focused, overwhelming effects at a single point. Simultaneous employment augments the effects of one element with that of another. Sequential employment sustains the effect longer than if just one element was used.


Figure 1-9. Reinforcing effects.

Effective Leaders Confront the Enemy with Dilemmas, Not Problems

1-106.  Leaders always seek to present the enemy with a dilemma, not just with problems. There are many ways to do this including, using combinations of weapons, different types of units, tactics, and terrain.

1-107.  In Figure 1-10 a moving enemy Infantry force makes contact with a stationary friendly Infantry force. There is an exchange of direct fire weapons. The direct fire contact poses a problem to which there is a solution. The universal reaction to direct fire contact is to get down and return fire. Once the situation develops, the direct fire effects, by themselves, tend to diminish as the enemy gets behind frontal cover and returns direct fire.

1-108.  Instead of making contact with direct fire, the friendly force may call for indirect fire. This, too, poses a problem that can be solved with a solution. The universal reaction to indirect fire is for the receiving unit to move out of the indirect fire burst radius. Once again, as the situation develops, the indirect fire effects, by themselves, tend to diminish as the enemy moves out of the burst radius to an area with overhead cover.

1-109.  Regardless of how lethal the effects of either direct fire or indirect fire are, by themselves they only pose problems that have solutions as their effects tend to diminish. Suppose the friendly force makes contact using both direct and indirect fire systems. What can the enemy do? He has a dilemma—if he gets up he gets shot, but if he stays down, he gets blown up. The enemy’s dilemma results from the complementary effects of direct and indirect fire. This is the essence of combined arms warfare.

Figure 1-10. Example of problem versus dilemma.

1-110.  To increase their effectiveness, leaders seek to combine both complementary and reinforcing effects. Continuing with the example from Figure 1-10, if the friendly Infantry has time, it can employ an obstacle to halt the enemy. The effects of the obstacle reinforce both the effects of direct and indirect fire. The synchronization of these three elements creates a “no-win” situation for the enemy. The engagement area development technique is designed using this as a foundation. Engagement area development combines the complementary effects of direct and indirect fire with the reinforcing effects of obstacles to produce an engagement area for killing enemy forces.

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