The Marines (海軍 Kaigun) are the Grand World World Government's military sea force, tasked with law enforcement, international security and military operations when needed. They are present in all the seas around the world, as evidenced by their branch offices. The focus of the plurality of their assets is on the far more dangerous Grand Line, as their main headquarters, Marineford, is located there.
The duty of the Marines is to maintain a law and order throughout the world and impose the will and might of the World Government. They are therefore considered the key strategic development force in the World Government and are expected to obey its orders at will. Sometimes these orders are questionable, however they are expected to carry them out regardless of opinion. Amongst their duties is awarding bounty hunters the bounties on the heads of a criminal. They tolerate bounty hunters as a method of making their job easier but are known to go out bounty hunting themselves. Apprehended criminals who are brought in alive are handed over to be made an example of, the Marines are left to ensuring the exportation of these criminals to prison and/or to their execution. Marines often work in pairs with one superior officer and a second in command or subordinate who is of slightly low rank. These partnerships may remain even during promotions with both pairs advancing in rank together. In the pair the higher ranked officer will give the orders to the men under their command, while the other acts an adviser or information gatherer while ensuring their partners command is undertaken by the men.
Higher ranked Marines (admirals and the fleet admiral) are expected to be on call to lead the Marine forces into war. This may take form of apprehending many criminals at once, protecting the World Nobles or calling a Buster Call to tackle a situation. Vice admirals are the ones who serve on the ships that the admirals call out and are tasked with carrying out the admirals orders exactly.
The main purpose of the Marines remain footed in the idea of bringing justice to any criminal. They use justice as their constituted policy to manage a world that is made entirely of one ocean much easier. However, the main problem within the Marines is the approach to Justice. They are generally divided between those who support Moral Justice and those who support Absolute Justice with the latter being the code of conduct for the Marines as a central doctrine. Nevertheless, there is little worry from the higher ranked Marines as to how the Justice is carried out so long as it is, leading those who truly support absolute justice to make questionable actions in carrying out their duties.
The Marines are also aided by the Shichibukai in terms of maintaining the "Three Great Powers", and as such, are expected to cooperate when necessary. Despite this, several Marines think of the Shichibukai as no more than pirates. In turn, the Shichibukai have no obligations to obey the Marines unless under the direct orders of the World Government itself.
One of the most questionable parts of their "Justice" is when it comes to Slavery. Despite the practice supposedly being abolished years before, it is often shown that they just look the other way. Especially when it comes to the World Nobles' slaves, where it is even seen as a crime to free said slaves even if the person is merely a child. Often they are tasked to find and retrieve the person to be a slave once again.
The system of military rank in place for the Marines is fairly straightforward, where each rank is clearly delineated.
Officers and recruits present at Marine Headquarters are considered "Super-elites". All ranks present from "Lieutenant" above are usually trained here, exceptions being those in command of other Marine bases.
The Marines do not have a system of rank insignia per se. There is significant variation in the kind of uniform worn by officers, with many opting to wear a variety of dress showcasing their own eccentric style. Marines are also allowed to wield whatever weapon they are most comfortable with, no matter how unusual it is. They are even free to fight bare-handed. However, as a general rule set down by the author, uniform guidelines are as follows:
- Upon first entering the Marines, new recruits are given the standard uniform, consisting of a white short-sleeved shirt emblazoned with the Marine emblem, a simplified seagull with "MARINE" underneath it, on the back; a blue neckerchief; dark blue trousers; and a baseball cap with "MARINE" across the front. All officers at the rank of Seaman (一等兵 Ittōhei) and below wear this. The quasi-rank of "Zatsuyō" (雑用 Zatsuyō) adds the kanji 雑 Zatsu ("various" or "odds and ends") to the sleeves, and to the Marine emblem on the back.
- Once an officer has reached the rank of Petty Officer (伍長 Gochō), he or she can choose from a number of different uniforms, including his or her personal clothes. Only those who really want to appear "sailor-like" will stay with a more traditional uniform. This uniform is generally the standard sailor outfit with red and blue epaulets.
- Sailors at the rank of Ensign (少尉 Shōi) and above are allowed to wear the coat with "Justice" (正義 Seigi) on the back. This coat tends to be worn like a cape, draped over the shoulders with the arms not in the sleeves. It should be noted that the sleeves of these coats are often much longer than the wearers' arms.
- For the rank of Lieutenant-Commander (少佐 Shōsa) and above, a suit worn underneath the "Justice" coat is the preferred attire.