Which command relationship involves units being an essential part of a military organization?

The command relationship in which units are considered an essential part of a military organization is organic. When a unit is described as organic, it means that it is a permanent element of a larger force, functioning under the command of that unit's headquarters and clearly integrated into the overall organization. This relationship ensures that the unit is a fundamental part of the mission and capabilities of the parent organization, providing a consistent and ready source of support.

In contrast, there are other command relationships, such as task organized and assigned, which may denote temporary arrangements or specific missions rather than an inherent part of the organization itself. Task organized units can be assembled for particular operations but may not necessarily be part of the headquarters's standard structure. Assigned units may fall under the control of another unit for a certain period but lack the deeper integration typical of organic units. Thus, organic is the most appropriate term for units that are essential and integrated into the military structure.