The Fire Nation's navy comprises coal-powered ironclad warships. In addition to its sturdy properties, the Fire Nation's use of metallurgy to remove impurities from the metal ensures that Earthbenders cannot damage their ships with their powers. These vessels serve many purposes, from ferrying and disembarking troops to providing bombardment with their catapults to creating blockades.
In one particular episode, captured Earthbenders were forced into labor to work on a mid-ocean shipyard, and knowing that they couldn't bend the metal of the rig, many of the captured Earthbenders lost their will to fight.
The Fire Nation's navy is very large; Admiral Zhao laid siege on the Northern Water Tribe with hundreds of ships, and the Fire Nation certainly has many more. However, almost all of that fleet was destroyed during Siege of the North, Part II when Aang became the physical incarnation of the ocean spirit, leaving only a few survivors to retreat.
since the rig was made of firenation metal it hade no earth fragments due top their propersmelting abilities
