Which of the following is NOT a use of illumination?

The correct answer is based on the specific purpose of illumination in military operations. Illumination is primarily used to enhance visibility during night operations, allowing forces to better assess and engage adversarial threats, adjust fire, and provide general situational awareness. The intention behind illumination includes illuminating areas suspected of adversary activity and providing the necessary visibility for the adjustment of indirect fires at night.

Although marking friendly locations can be crucial during combat operations, particularly for aerial support like Close Air Support (CAS), it is not a primary use of illumination. Illumination focuses on improving visibility and situational awareness rather than specifically marking positions. Usage for marking friendly locations typically involves other means, such as signaling devices or navigational aids, rather than lighting up an area.

When considering the other uses provided, illuminating areas of suspected adversary activity directly aids in targeting and threat assessment, while the provision of light for night adjustment of fires is essential for accuracy and safety in live-fire operations. Additionally, the use of illumination for harassment serves to disrupt the adversary and diminish their operational effectiveness, albeit indirectly.