Which report displays a unit's personnel strength in aggregate numbers and is used to assess combat power?

The PERSUM report is the correct choice because it specifically provides a comprehensive overview of a unit's personnel strength in aggregate numbers. It summarizes the total number of personnel available, indicating the unit's readiness and ability to deploy or engage in combat operations. The PERSUM is vital for command decisions, allowing leaders to assess the combat power and logistical needs of the unit, ensuring they have the appropriate force strength to meet operational goals.

In contrast, the other report types listed serve different purposes. The PRR (Personnel Readiness Report) generally focuses on individual readiness statuses rather than providing an aggregated strength number. The PERSTAT (Personnel Status Report) gives detailed information about individual soldiers' statuses but may not focus on an overall strength assessment in combat terms. JPERSTAT (Joint Personnel Status Report) is used in a joint or coalition environment for tracking personnel, but it is not primarily designed for an aggregated personnel strength assessment. Thus, PERSUM stands out for its specific goal of evaluating unit strength in aggregate numbers.