Which action provides the legal authority to create a new military unit?

The action that provides the legal authority to create a new military unit is "constitute." To constitute a military unit means to officially establish it within the command structure, granting it legal recognition and defining its structure, purpose, and operational parameters. This process often involves formal orders and documentation that outline the unit's formation, ensuring it is recognized by higher command as a legitimate part of the military organization.

In contrast, activating a unit typically refers to bringing an existing unit into active service from a reserve status, while assigning involves placing a unit under the command of a particular officer or branch for a specific mission or task. Designation refers to naming or labeling a unit rather than creating it. Therefore, while all these actions relate to the management of military units, only constituting a unit pertains directly to the legal establishment of a new military formation.