Just as the President, the Secretary of Defense, and the Secretary of Homeland Security, are in charge of the entire military establishment, maintaining civilian control of the military, so too are each of the Defense Department's constitutive military departments headed by civilians. The four DoD branches are organized into three departments, each with civilian heads. The Department of the Army is headed by the Secretary of the Army, the Department of the Navy is headed by the Secretary of the Navy and the Department of the Air Force is headed by the Secretary of the Air Force. The Marine Corps is organized under the Department of the Navy, however it is still considered a separate and equal service. The Coast Guard is under the Department of Homeland Security and receives its operational orders from the Secretary of Homeland Security. However, the Coast Guard may be transferred to the Department of the Navy by the President or Congress during a time of war, thereby placing it within the DoD.
The operational level is at a scale bigger than one where line of sight and the time of day are important, and smaller than the strategic level, where production and politics are considerations. Formations are of the operational level if they are able to conduct operations on their own, and are of sufficient size to be directly handled or have a significant impact at the strategic level. This concept was pioneered by the German army prior to and during the Second World War. At this level, planning and duration of activities takes from one week to a month, and are executed by Field Armies and Army Corps and their naval and air equivalents.
Personnel may be posted to bases in their home country or overseas, according to operational need, and may be deployed from those bases on exercises or operations anywhere in the world. During peacetime, when military personnel are generally stationed in garrisons or other permanent military facilities, they mostly conduct administrative tasks, training and education activities, technology maintenance, and recruitment.