Which term describes the action of establishing security during an operation?

The term that describes the action of establishing security during an operation is "Security." This concept encompasses the measures taken to protect personnel, equipment, and information from threats or potential dangers that may arise during military operations. Establishing security is critical to ensure that forces can operate effectively and maintain their combat capability without interference from adversaries. It involves both proactive measures to deter threats and defensive actions to safeguard against potential attacks.

When forces establish security, they may implement various strategies and tactics that include establishing perimeters, conducting patrols, and setting up defensive positions, all aimed at providing a protective layer around operational elements. This is a crucial aspect of military operations, as it allows for safe movement and operation of troops and resources while reducing vulnerability.

In contrast, the other terms relate to different aspects of military operations. Engagement refers to the actual combat or confrontation between forces. Support involves providing assistance or logistical aid to enhance an operation's effectiveness. Reconnaissance is the task of gathering information about the enemy or the operational environment, typically to inform strategic or tactical decisions. None of these terms specifically address the establishment of protective measures, which is why "Security" is the most appropriate choice in this context.