Nautilus

The Nautilus is an sirship in Final Fantasy III. It is obtained after defeating the Garuda boss in Southwestern Saronia's Dragon Spire. Of the three airships in the game, it is unique because it the only one that can dive underwater. While in this submarine form, the party can explore the ocean floor and explore several dungeons that were previously inaccessable. The Nautilus is still availble for the party to use after the Invincible is obtained, and is faster than the Invicible, but lacks the healing, shop, and Fat Chocobo benefits.