Shark Submerge III

The Shark Submerge III is a deep-sea exploring submarine shaped as a shark that can carry three people. Used in the Thousand Sunny's Soldier Dock System, deployed by the number 3. It also has a Den Den Mushi.

There is a high chance this ship will be used when the crew need to go to mermaid island as Kokoro said it was underwater.

Anime and Manga Differences
Originally in the manga, the Shark Submerge was first shown when the Straw Hats when Franky explained about the Soldier Dock System in Thriller Bark. While shown, however, it hasn't yet been used in the manga. In the anime, the Shark Submerge was first shown and used during the Ice Hunter Arc.