Captain (United States O-6)
In the United States Navy and United States Coast Guard, the United States Public Health Service Commissioned Corps, and the National Oceanic and Atmospheric Administration Commissioned Officer Corps, captain is the senior-most commissioned officer rank below that of flag officer (i.e., admirals). Reflecting its nautical heritage, it also sometimes used as a military "title" by more junior officers who are serving as the commanding officer (CO) of a commissioned vessel of the Navy or Coast Guard of patrol boat size or greater, while officers below O-6 commanding aviation squadrons (typically O-5 commanders) or shore activities will use the title of "skipper." (see rank vs. title)
The star, shoulder boards, and sleeve stripes of a U.S. Navy captain (Line officer)
In the United States Navy, captain (abbreviated CAPT) is a senior officer rank, with the pay grade of O-6. It ranks above commander and below rear admiral (lower half). It is equivalent to the rank of colonel in the other uniformed services. Promotion to captain is governed by Department of Defense policies derived from the Defense Officer Personnel Management Act (DOPMA) of 1980. DOPMA guidelines suggest that no more than 50% of eligible commanders should be promoted to captain after serving a minimum of three years at their present rank and after attaining 21–23 years of cumulative commissioned service.
Navy captains with sea commands in the surface warfare officer community generally command ships of cruiser size or larger. The more senior the officer, the larger the ship. Others may hold command as commodores of destroyer squadrons (DESRON) consisting of multiple destroyers and frigates. Surface Warfare Officers may also command large deck amphibious warfare ships or combat support ships and also serve as commodores of amphibious squadrons.
In the submarine community, a captain will typically command a ballistic-missile submarine (SSBN), or a squadron of attack submarines (SSN). Like their surface warfare counterparts, they may also serve as commodores of submarine squadrons (SUBRON), commanding a group of submarines.
In Naval Aviation, captains with sea commands are Naval Aviators or Naval Flight Officers who are commanding officers or executive officers of aircraft carriers or commanders of air-capable amphibious assault ships, commanders of carrier air wings (CAG), or commodores of functional or "type" air wings or air groups. A smaller cohort outside of sea commands may also serve as astronauts on loan to the National Aeronautics and Space Administration (NASA).
In the Naval Special Warfare "Sea Air Land" (SEAL) community, captains with sea commands are typically commodores in command of Naval Special Warfare Groups (NAVSPECWARGRU).
In contrast, commanders of aircraft carrier strike groups (CSG) and expeditionary strike groups (ESG) are normally rear admirals, while subordinate destroyer squadron commodores, amphibious squadron commodores, carrier air wing commanders and the individual ship commanding officers within the strike group are of captain rank or lower. In rare instances, the carrier air wing commander may be a Marine Corps colonel who is a Naval Aviator or Naval Flight Officer; while in the expeditionary strike group, the Marine Expeditionary Unit (MEU) commanding officer will always be a Marine Corps colonel. Adding to the confusion, all commanding officers of Navy ships and submarines are called "captain" regardless of actual rank.
Navy captains who are line officers may also fill important senior staff positions as Chiefs of Staff or Executive Assistants to flag officers, or have shore based command assignments, such as commanding officers of naval bases, naval stations, naval air stations, naval air facilities, naval support activities, logistics groups, specialized centers or schools, or commanders of test wings or training air wings. They may also occupy senior leadership positions on fleet staffs, naval component commands staffs, the staffs of the joint Unified Combatant Commands, the staff of the Chief of Naval Operations (OPNAV), or the Joint Staff.
As opposed to line officer captains, staff corps captains will command facilities and organizations appropriate to their designators, such as naval hospitals commanded by medical corps, dental corps, medical service corps or nurse corps officers; supply centers by supply corps officers; or trial service offices commanded by judge advocate general corps officers.
U.S. Coast Guard
The United States Coast Guard also uses the naval rank system. A Coast Guard captain ranks above a commander and below rear admiral (lower half). The sleeve and shoulder board insignia are similar to the Navy insignia, with a lighter shade of blue with a gold USCG shield above the stripes. Coast Guard captains follow career paths very similar to their Navy counterparts, with seagoing officers typically commanding large maritime security cutters or high endurance cutters and aviators commanding coast guard air stations. Coast Guard captains will also command all types of major Coast Guard shore installations and activities, as well as serve as chiefs of staff for Coast Guard flag officers. The Coast Guard has no staff corps officers.
U.S. Public Health Service and NOAA
In the United States Public Health Service, and in the National Oceanic and Atmospheric Administration Commissioned Officer Corps, captains are senior non-combatant officers that serve as directors or ranking supervisors in their respective uniformed service corps. Seagoing NOAA captains will command certain NOAA ships, while NOAA aviators will command NOAA flight operations activities. USPHS rapid deployment force teams, containing 105 PHS physicians, nurses, and other medical professionals, are exclusively commanded by captains.
U.S. Maritime Service
Although it exists largely as a maritime training organization, the United States Maritime Service also uses the rank of captain. Even though the Maritime Service is an auxiliary service, the grade is appointed by the President via the Secretary of Transportation, making it a federally recognized rank with corresponding paygrade of O-6.
|United States commissioned officer and officer candidate ranks|
|Pay grade / Branch of service||Officer
|Air Force||Cadet / OT / OC||2d Lt||1st Lt||Capt||Maj||Lt Col||Col||Brig Gen||Maj Gen||Lt Gen||Gen||GAF|||
|Army||CDT / OC||2LT||1LT||CPT||MAJ||LTC||COL||BG||MG||LTG||GEN||GA||GAS|
|Marine Corps||Midn / Cand||2ndLt||1stLt||Capt||Maj||LtCol||Col||BGen||MajGen||LtGen||Gen|||||
|Navy||MIDN / OC||ENS||LTJG||LT||LCDR||CDR||CAPT||RDML||RADM||VADM||ADM||FADM||AN|
|Coast Guard||CDT / OC||ENS||LTJG||LT||LCDR||CDR||CAPT||RDML||RADM||VADM||ADM|||||
|Public Health Service||[OC]||ENS||LTJG||LT||LCDR||CDR||CAPT||RADM||RADM||VADM||ADM|||||
Unofficial 1945 proposal for General of the Armies insignia; John J. Pershing's GAS insignia: ; George Dewey's AN insignia:
 Rank used for specific officers during World War II and Korea only, not permanent addition to rank structure
 Grade is authorized by the U.S. Code for use but has not been created
 Grade has never been created or authorized
|United States warrant officer ranks|
|Public Health Service|||||||||||
|National Oceanic and
 Grade is authorized for use by U.S. Code but has not been created
 Grade never created or authorized