Which sustainment function directly affects the operational reach of military units?

The sustainment function that directly affects the operational reach of military units is logistics. Logistics encompasses the planning and execution of the movement and support of forces, which includes the transportation of troops, equipment, supplies, and sustaining operations in the field. It directly influences a unit's ability to maintain its operational capabilities over distance and time.

Operational reach is defined as the distance and duration across which a force can successfully employ military capabilities. Logistics ensures that units are adequately supplied, supported, and equipped, which is essential for extending this reach. Without a solid logistics foundation, units would struggle to sustain their operations, impacting their effectiveness and capacity to engage in prolonged missions.

Other functions, while important, do not specifically address the logistical needs that underlie operational reach. Freedom of action pertains to a unit's ability to maneuver and operate without restrictions. Health service support focuses on the medical aspects of sustaining forces rather than the logistical support necessary for operational continuity.