Captain is a title, an appellative for the commanding officer of a military unit; the supreme leader or highest rank officer of a navy ship, merchant ship, aeroplane, spacecraft, or other vessel; or the commander of a port, fire or police department, election precinct, etc. In militaries, the captain is typically at the level of an officer commanding a company or battalion of infantry, a ship, or a battery of artillery, or another distinct unit. It can also be a rank of command in an air force. The term also may be used as an informal or honorary title for persons in similar commanding roles.