Which method of control allows the observer to specify the specific time rounds impact on the target?

The method of control that allows the observer to specify the exact time rounds impact the target is "Time on Target." This technique involves coordinating the timing of artillery or mortar rounds so that they all arrive at the target simultaneously. The observer can dictate a precise time for the rounds to impact, which is critical for maximizing the effectiveness of the fire support and ensuring that all rounds converge on the target at the desired moment. This method is particularly useful for creating a coordinated and overwhelming impact on the target area.

In contrast, "Time to Target" involves specifying how long it takes for the rounds to reach the target after they are fired, which does not provide the same level of control over the exact moment of impact. "Request Time" generally refers to the anticipated time for a fire mission rather than a control method for impact synchronization. "Duration" may refer to the length of time that fire is sustained or the overall fire support plan but does not specifically address the timing of individual rounds impacting a target.