Officer of the line

In the United States Armed Forces, the term line officer or officer of the line refers to a U.S. Navy, U.S. Marine, U.S. Air Force, or U.S. Coast Guard commissioned officer who exercises general command authority and is eligible for operational command positions, as opposed to officers who normally exercise authority within a specialty. The term is not generally used by officers of the U.S. Army – the roughly corresponding Army terms are basic branch and special branch, although the concepts are not synonymous as some special branch Army officers are eligible to hold command.

Officers who are not line officers are those whose primary duties are in non-combat specialties including chaplains, attorneys, supply, and medical services. A line officer may hold authority over a non-line officer of higher rank by the nature of their assignment or appointment/succession to command, but is otherwise expected to observe normal customs and courtesies outside that role.

See explanation of staff and line.

The expression "officer of the line" is possibly rooted in the 18th- and 19th-century Royal Navy practice of employing sail-powered warships in line formations to maximize the effectiveness of side-mounted cannons. The ships were called ships of the line and their officers were termed line officers. The term also derives from "walking the line" and in many military circles is believed to have come from a "line in the sand" which two groups of officers once used in a political argument to gain power.

In the United States Navy (and USN Reserve), line officers are divided into unrestricted line officers and restricted line officers. Unrestricted Line (URL) officers hold combat warfare specialties as Naval Aviators and Naval Flight Officers, Surface Warfare Officers, Submarine Warfare Officers, and Naval Special Warfare/Naval Special Operations (NSW/NSO) officers (consisting of SEALs, Special Warfare Combatant-Craft (SWCC) Warrant Officers, Explosive Ordnance Disposal (EOD) officers, and Navy diving officers), and are eligible for operational combatant command at sea, as well as command of major installations and commands ashore. Restricted Line officers command only within their particular specialty, and are normally in fields such as intelligence, cryptology, oceanography/meteorology, engineering duty, aeronautical engineering duty, aircraft maintenance, public affairs, etc.

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