Which method of control would an observer use to specify when rounds should impact on the target?

The method of control that allows an observer to specify when rounds should impact on the target is "Time on Target." This method is crucial in artillery operations as it enables the observer to coordinate a simultaneous impact of multiple rounds on a specific target or area. By setting a designated time for the shells to detonate, an observer can maximize the effectiveness of the fire by catching the enemy off guard or creating a concentrated effect against a target at a precise moment.

In contrast, other methods such as "Time to Target" focuses on the time it takes for a projectile to reach the target after being fired, which does not allow for precise scheduling of impacts. "Request Time" is not a standard term utilized in artillery procedures and may create confusion regarding timing and coordination. "Duration" generally refers to the length of time that fire is sustained rather than a specific point of impact. Understanding these distinctions reinforces why "Time on Target" is the preferred method for achieving precise control over artillery fire impacts.