The CSS Birmingham was, originally, a Confederate Ironclad warship sunk at the bottom of the sea, until the war god, Ares, raised it from the depths so Clarisse may have transportation and a crew to escort her to the Sea of Monsters. It is not meant for use in deep water.
Ares raised the CSS Birmingham to serve Clarisse La Rue in her quest because, as Clarisse explained, the losing side of any war owed a debt to Ares. After rescuing Percy Jackson and Annabeth Chase from a Hydra attack, the ironclad departs for the Sea of Monsters, otherwise known to mortals as the Bermuda Triangle. When entering the Sea of monsters guarded by Scylla and her sister, the ship's engines started to overheat and although Tyson delayed it, the ship exploded. Percy, Annabeth, and Clarisse managed to escape in the nick of time. Percy and Annabeth wash up on the shores of Circe's Island, while Clarisse ends up at Polyphemus's island.