Captain, a military and naval rank. The word comes from the Latin caput, meaning “head.” In the U.S. Army, U.S. Air Force, and U.S. Marine Corps, a captain ranks below a major and above a first lieutenant.
An Army or Marine captain ordinarily commands a company. An Air Force captain commands a flight, a unit of usually four planes. In these services, the rank of captain is designated by two parallel silver bars.
In the U.S. Navy, a captain ranks below a rear admiral lower half and above a commander. He or she corresponds in rank to a colonel in the Army, Air Force, or Marine Corps. A captain's rank is shown by a silver eagle worn on the collar and four stripes of equal width worn on the shoulder boards or on the jacket sleeves. A Navy captain ordinarily commands an aircraft carrier, a cruiser, a destroyer squadron, or a large shore station. Coast Guard captains usually command their service's largest vessels, such as icebreakers and cutters. By naval custom, the commander of any ship, whatever the rank, is called captain.
In the U.S. Merchant Marine and in all other shipping services, the officer in charge of a ship is called captain. By ancient custom of the sea, the captain of a ship has almost unlimited powers.