Captain (Marine Rank), One Piece Wiki

For the person in charge of a pirate crew, see Pirate Captain. Captain is the sixth highest rank in the Marines. The rank of a marine officer who commands a ship would not necessarily be "Captain". It may be higher (up to Fleet Admiral), or lower on small ships. By naval custom, any officer who is below the rank of Captain and commands a ship is addressed as "captain" while aboard that ship. The ship's captain also may be referred to as the Skipper. See also the associated category: Marine Capta

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