 For the naval rank, a captain is a senior officer of U.S. uniformed services pay grades O-6 (the sixth officer rank), typically commanding seagoing vessels, major aviation commands and shore installations.This rank is used by the U.S. Navy, U.S. Coast Guard, U.S. Public Health Service Commissioned Corps, the NOAA Commissioned Corps, and the U.S. Maritime Service.Seaborne services of the United States and many other nations refer to the officer in charge of any seagoing vessel as "captain" regardless of actual rank.