To maintain peace in the oceans, the PKN was established, comprising state‑of‑the‑art warships from several nations. During its foundation ceremony, the organization was raided by the unidentified group USR, who sought world domination. The attackers captured the submarine UX, commanded by Admiral Red of the USR. An old Japanese submarine, the 707, rescued the PKN, with Captain Hayami risking his life to operate it. One year later, after the 707 had been destroyed in the previous battle, the newly developed submarine 707 II set sail. Among its crew were trainee boys Kenji, Goro, and Senta. PKN formed a fleet led by the Great G…