What term refers to the force designated to engage the main enemy force directly?

The term that refers to the force designated to engage the main enemy force directly is "main effort." This concept is crucial in military operations, as the main effort represents the primary focus and concentration of combat power aimed at achieving the overall mission objectives against the enemy.

In this context, the main effort is where the commander allocates the majority of resources, personnel, and firepower, ensuring that this force is appropriately supported and prioritized. By designating a main effort, a unit can effectively coordinate actions and maneuvers to achieve decisive outcomes in battle, while also allowing for flexibility in resource deployment in response to changing battlefield conditions.

The other terms refer to different roles within the overall operation. Supporting effort involves secondary forces that assist the main effort and can also engage the enemy but typically do so with a narrower focus. Reserves are held back for reinforcement or reactionary actions to exploit breakthroughs or respond to unfolding threats. Advance units serve as the forward elements that gather intelligence and secure areas but are not necessarily tasked with direct engagement of the enemy's main force. Each of these plays a role in a comprehensive operational strategy, but it is the main effort that takes center stage when it comes to directly confronting the primary enemy forces.