Line officer In the United States armed forces , the term line officer or officer of the line refers to a Navy , Marine , Air Force or Coast Guard 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 equivalent Army term is " competitive category " . Officers who are not line officers are those whose primary duties are in non - combat specialties including chaplains , attorneys , and medical services . The distinction between line and non - line officers often blur ; line officers may be assigned non - combat roles , and non - line officers are often assigned to tasks normally performed by line officers . Also , non - line officers at the squadron or Group level ( and higher ) are also issued " G - Series " orders which gives them the same relative power of ' line officers ' of equivalent rank . A line officer may even hold authority over a non - line officer of higher rank by the nature of their job , but is otherwise expected to observe normal customs and courtesies outside that role . History . 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 . United States forces . In the United States Navy , line officers are divided into unrestricted line officer s and restricted line officer s . Unrestricted Line ( URL ) officers hold combat warfare specialties as Naval Aviators and Naval Flight Officers , Surface Warfare Officers , Submarine Warfare Officers and / or Special Warfare ( SEAL ) 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 . Line officers wear an inverted gold star above their rank stripes on their dress blue uniforms and , in the case of Captains and below , on their shoulder boards in whites . Line officer admirals will wear solid gold shoulder boards with a silver metallic thread anchor and one , two , three or four silver metallic thread stars below the anchor . When wearing khakis or utility / working uniforms , they wear their rank insignia on both collar points . The Navy refers to non - line officers as Staff Corps officers . Both Line and Staff Corps officers may be assigned as " staff officers " serving on the staff of a senior officer . Staff Corps officers wear their corps insignia , rather than the line officer ' s star , placed over their sleeve / shoulder board stripes on blues and whites and on their left collar point on khakis and utility / working uniforms . In the United States Marine Corps , all officers including warrant officer s and limited duty officer s ( LDOs ) are line officers , trained to command combat units . Unlike the Navy , the Marine Corps does not have Staff Corps , consequently all Marine Engineer , Supply , and Judge Advocates are line officers . The Marine Corps , as a service under the Department of the Navy also lacks its own medical corps officers , dental corps officers , nurse corps officers and chaplains . These positions are filled by US Navy staff corps officers in those specialties assigned to the Fleet Marine Force . In the United States Air Force , officers assigned to the Medical , Judge Advocate , Nurse , Medical Services ( healthcare administration ) , Biosciences , and Chaplain Corps are " professional " officers . All other officers belong to the Line of the Air Force ( LAF ) . All officers of the United States Coast Guard are considered line officers and wear the Coast Guard shield in lieu of the inverted star . Other forces . The expression " line officer " is no longer current in the Royal Navy and Commonwealth affiliates , officers trained in the " Executive Department " of a warship are the only ones trained for command . In the Royal Canadian Navy , officers in the Maritime Surface / Sub - Surface ( MARS ) occupation hold a similar function , but are not distinguished by any identifiable badge .