What is considered key terrain whose seizure is mandatory for mission success?

Decisive terrain is defined as key ground that, when controlled or seized, significantly enhances the operational effectiveness of a unit and increases the likelihood of mission accomplishment. In many military operations, certain pieces of terrain can dictate the flow of the battle and can provide a strategic advantage to the forces that hold it. This terrain often includes locations that offer a clear view of enemy movements, advantageous cover, or critical routes for maneuvering.

In this context, when decisive terrain is seized by a unit, it can serve to enhance their capability to conduct operations effectively, such as controlling lines of communication or obstructing enemy movement. The importance of decisively controlling this type of terrain makes its seizure a mandatory action for ensuring success in the mission.

The other options, while related to battlefield operations, do not inherently indicate the necessity of control for mission success in the way that decisive terrain does. Trigger lines are relevant in planning and initiating action based on certain criteria, maximum engagement lines set ranges for weapon engagement, and assault positions denote locations where forces prepare to attack but do not inherently hold the same level of strategic importance as decisive terrain.