Military ranks are a system of hierarchical relationships, within armed forces, police, intelligence agencies or other institutions organized along military lines. The military rank system defines dominance, authority, and responsibility in a military hierarchy. It incorporates the principles of exercising power and authority into the military chain of command—the succession of commanders superior to subordinates through which command is exercised. The military chain of command constructs an important component for organized collective action.
Ensign is a junior rank of a commissioned officer in the armed forces of some countries, normally in the infantry or navy. As the junior officer in an infantry regiment was traditionally the carrier of the regimental colours, the rank acquired the name. This rank has generally been replaced in army ranks by second lieutenant. Ensigns were generally the lowest-ranking commissioned officer, except where the rank of subaltern existed. In contrast, the Arab rank of ensign, لواء, liwa', derives from the command of units with an ensign, not the carrier of such a unit's ensign, and is today the equivalent of a major general.
In the United States Armed Forces, a line officer or officer of the line is a U.S. Navy or U.S. Marine Corps commissioned officer or warrant officer who exercises general command authority and is eligible for operational command positions, as opposed to officers who normally exercise command authority only within a Navy Staff Corps. The term line officer is also used by the U.S. Air Force and U.S. Coast Guard to indicate that an officer is eligible for command of operational, viz., tactical or combat units. The term is not generally used by officers of the U.S. Army – the roughly corresponding Army terms are basic branch and special branch qualified officers, although the concepts are not entirely synonymous, as some Army special branch officers are eligible to hold command outside their branch specialty.
A limited duty officer (LDO) is an officer in the United States Navy or United States Marine Corps who was selected for commissioning based on skill and expertise. They are the primary manpower source for technically specific billets not best suited for traditional Unrestricted Line, Restricted Line, or Staff Corps career path officers. Per Title 10, U.S. Code, an LDO is a permanent commissioned officer appointed under section 8139 in a permanent grade above chief warrant officer, W-5, and designated for limited duty.
Commodore was an early title and later a rank in the United States Navy, United States Coast Guard and the Confederate States Navy, and also has been a rank in the United States Public Health Service Commissioned Corps and the National Oceanic and Atmospheric Administration Commissioned Officer Corps and its ancestor organizations. For over two centuries, the designation has been given varying levels of authority and formality.
In the United States Navy, commissioned officers are either line officers or staff corps officers. Staff corps officers are specialists in career fields that are professions unto themselves, such as physicians, lawyers, civil engineers, chaplains, and supply specialists. For example, a physician can advance to become the commanding officer (CO) of a hospital, the medical hospital on a hospital ship or large warship, or a medical school; or the Chief of the Medical Corps or of the Bureau of Medicine and Surgery. A supply officer can become the CO of a supply depot or a school, or the head of the Naval Supply Systems Command, etc.
In the United States Armed Forces, the ranks of warrant officer are rated as officers above all non-commissioned officers, candidates, cadets, and midshipmen, but subordinate to the lowest officer grade of O‑1. This application differs from the Commonwealth of Nations and other militaries, where warrant officers are the most senior of the other ranks, equivalent to the U.S. Armed Forces grades of E‑8 and E‑9.
In the uniformed services of the United States, captain is a commissioned-officer rank. In keeping with the traditions of the militaries of most nations, the rank varies between the services, being a senior rank in the naval services and a junior rank in the ground and air forces. Many fire departments and police departments in the United States also use the rank of captain as an officer in a specific unit.
United States Marine Corps rank insignia are the devices worn by officers in the United States Marine Corps, in order to provide distinction from other ranks. Different styles of rank insignia are worn on different uniforms of the United States Marine Corps.
United States Coast Guard officer rank insignia describes an officer's pay-grade. Rank is displayed on collar devices, shoulder boards, and on the sleeves of dress uniforms.
A rear admiral in the uniformed services of the United States is either of two different ranks of commissioned officers: one-star flag officers and two-star flag officers. By contrast, in most other countries, the term "rear admiral" refers only to an officer of two-star rank.
The United States Navy has nearly 500,000 personnel, approximately a quarter of whom are in ready reserve. Of those on active duty, more than eighty percent are enlisted sailors, and around fifteen percent are commissioned officers; the rest are midshipmen of the United States Naval Academy and midshipmen of the Naval Reserve Officer Training Corps at over 180 universities around the country and officer candidates at the navy's Officer Candidate School.
An officer is a person who holds a position of authority as a member of an armed force or uniformed service.
In the United States Navy, United States Coast Guard, United States Public Health Service Commissioned Corps (USPHS), and National Oceanic and Atmospheric Administration Commissioned Officer Corps, captain is the senior-most commissioned officer rank below that of flag officer. The equivalent rank is colonel in the United States Army, Air Force, Space Force, and Marine Corps.
