In the United States Navy and United States Coast Guard, the United States Public Health Service Commissioned Corps (USPHS), and the National Oceanic and Atmospheric Administration Commissioned Officer Corps (NOAA), captain is the senior-most commissioned officer rank below that of flag officer (i.e., admirals). Reflecting its nautical heritage, it is 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) will usually use the title of "skipper." (see rank vs. title)