A fire support coordination measure that requires coordination with affected commanders before engagement is known as what?

The correct answer is the Fire Support Coordination Line (FSCL). This measure is crucial in joint and combined operations where multiple commanders and units may be operating in close proximity. The FSCL is established to enhance coordination between different units and minimize the risk of fratricide. It designates the boundary beyond which fire support can be coordinated without the need for further deconfliction or coordination with the affected commanders.

When a unit intends to engage targets beyond the FSCL, it must coordinate with the affected command units to ensure that there is no interference with their operations. This emphasis on coordination is vital for maintaining operational effectiveness and ensuring the safety of all forces involved. The FSCL allows for streamlined communication and responsiveness in fire support operations by clearly outlining the areas where authority and coordination are required.

This method differs fundamentally from the other options, which serve distinct purposes. A Coordinated Fire Line allows all fires to engage targets without prior coordination, whereas a Free Fire Area allows for engagement of targets without needing that same level of coordination, and Phase Lines serve as references for movement and command rather than fire support engagement. Thus, the FSCL's requirement for coordination before engagement sets it apart as a critical fire support measure.