C-8. Echelonment of fires is the schedule of fire ranging from the highest caliber munitions to the lowest caliber munitions. The purpose of echeloning fires is to maintain constant fires on the enemy while using the optimum delivery system. Leaders use risk estimate distance, surface danger zones, and MSD to manage associated risks. In the defense, triggers are tied to the progress of the enemy as it moves through the area of operation, enabling the leader to engage the enemy throughout the depth of the area of operation. In the offense, triggers are tied to the progress of the maneuver element as it moves toward the objective protecting the force and facilitating momentum up to the objective.