Captain (Marine Rank)

"Captain" (大佐) 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 Taisa and commands a ship is addressed as "captain" while aboard that ship. The ship's captain also may be referred to as the Skipper.

Duties
One of the duties that a Marine captain could have is commanding one of the several Marine branches established on the islands around the world. In addition, a captain is often seen navigating the seas in order to capture pirates and keep order. In these cases, the captain is the leader of the ship as long there are no higher-ranking Marines on board.

Abilities
Marine captains are strong Marine officers whose experience and battle performance are forces to be reckoned with. Most of the several Marine captains seen in the series are powerful fighters with Devil Fruit powers, high combat skills, and/or considerable tactical knowledge. They are usually in charge of lower ranking marines and some like Morgan and Nezumi are the commander in charge of Marine Bases. Some Captains like Tashigi serve under other higher ranked Marines, as she has been Smoker's subordinate both when he was a Commodore and as a Vice Admiral. As shown by Nezumi, Captains can use their position to alert their superiors to potential threats and dangerous pirates, resulting in Bounties for the criminal and/or pirate being issued as was the case with Monkey D. Luffy's first bounty. Due to their combat skills, abilities, and experience, they serve on Buster Call ships under the command of Vice Admirals in charge.

While some Captains possess Devil Fruit powers, some like Tashigi and Koby simply possess high combat skills (swordsmanship or martial arts prowess), the ability to use Haki, or knowledge of Rokushiki techniques like Soru.

Abuses of Rank and Corruption
Some captains like Morgan and Nezumi have been known to abuse the position (terrorizing and/or abusing civilians and even their own subordinates), neglect their duties (ignoring pirate oppression of civilians and/or not putting any effort into capturing pirates), and/or engage in acts of corruption (taking bribes from criminals/pirates, extorting money from civilians, or even working in conjunction with wanted criminals/pirates). However, as shown with Morgan, if any of these misuses of their position or criminal corruption are exposed, they can be stripped of their rank and imprisoned. Due to the Marine's code of Absolute Justice, the hypocrisy of the World Government (slavery and the World Nobles), and abuses by other Government employees/subordinates (from CP9's Spandam to Shichibukai like Crocodile and Doflamingo), such cases like Morgan's are rare. Nezumi managed to retain his position as he was able to cover up his illegal arrangement with Arlong and Vergo was promoted to Vice Admiral due to the Marine's being unaware that he was actually the Donquixote Pirates' mole.