The Fire Nation military also makes use of coal mines and prisons. The prisons are segregated facilities in which prisoners from other nations are forced to labor. Made of metal, one such facility can be a stationary shipyard situated in the middle of the ocean. Bisected by an enormous wall, one side is used as the shipyard where warships are repaired and refueled, while the other side serves as a prison for captive Earthbenders. Surrounded by the sea and miles away from solid, earthen land, the benders are rendered powerless. However their muscular strength is not wasted, as the wardens force them to labor away in the shipyard, building new ships for the Fire Nation navy to be later used as aid in the conquest of their own Kingdom
