The Poseidon is a flying ship used within two versions of Cyborg 009.
In its first incarnation seen in the Cyborg 009: SF Roman light novel, it is for all intents and purposes a renamed Dolphin, sharing the same role that the ship did in the Underground Empire of Yomi arc.
In the manga, it is the ship used in the penultimate 1980 arc The Legend of the Star Mermaid, as the cyborgs navigate the planet Reptum.