What is established when a unit's headquarters is activated?

When a unit's headquarters is activated, the term "Establishment" signifies the formal initiation of that unit's operations and the affirmation of its administrative structure. This process signifies that all the necessary personnel, resources, and protocols are in place and ready to function effectively. Establishment specifically refers to the formal recognition and setup of the unit, ensuring that all elements are operational and aligned with the mission at hand.

In contrast, "Formation" pertains to the organizational makeup or structure of military units, while "Activation" usually refers to the process of putting a unit into active service. "Deployment" involves the movement of forces to a specific location for operations, but it doesn’t specifically denote the initiation of a unit's headquarters or its organizational status. Therefore, the correct term to describe the situation when a unit's headquarters is activated is "Establishment."