This unit is designed to use the most dangerous of all naval weapons - fire.
A city must have at least one exploited sea or lake tile where the Fire Ship will spawn upon completion, which is normally designated by a movable Anchor icon in the city screen. If there is a naval army on that tile owned by the owner of the city with room for more units, the Fire Ship will automatically be merged into that army upon completion. If the designated tile is occupied by an army with no more room, an enemy naval army, a transport ship, or a tile of ice shelf during winter, the Fire Ship will spawn on the nearest available exploited sea or lake tile. If there are no available sea or lake tiles, construction of the Fire Ship cannot be completed.