What is the name of a phase line used to initiate mass fires into an engagement area?

The term "Trigger Line" is used to refer specifically to a phase line established to initiate mass fires into an engagement area. This line is crucial in military operations as it designates a boundary at which units are authorized to commence fire against target areas or enemy forces once they reach this designated point. By defining this line, commanders ensure synchrony and timing in the execution of mass fires, allowing for effective coordination among different elements of the force.

This concept is essential in situational awareness and mission planning, as it provides clear commands to fire support teams. When units cross this line, they understand it is the signal to engage with their weapon systems, maximizing the firepower at play during an operation.

In terms of the other provided choices, they have specific functions in military operations but do not designate a phase line to initiate mass fires in the same manner. Support by Fire Position refers to a location from which forces can provide covering fire but does not function as a trigger for mass fire. The Maximum Engagement Line generally pertains to the range limitations of weapon systems rather than a tactical initiation line. Decisive Terrain indicates key geographical features or obstacles that can influence the outcome of engagements but does not specifically initiate fire support.