Submarine 707R

PKN was established to maintain peace in the oceans, using advanced warships from different countries. During its founding ceremony, it was attacked by the unknown group USR, which seeks global domination. Their most powerful asset was the submarine UX, commanded by Admiral Red. A damaged Japanese submarine, the 707, piloted by Captain Hayami, intervened to stop them. A year later, the 707 II, a new version of the submarine, was launched with former trainees like Kenji, Goro, and Senta among the crew. PKN's fleet, led by the U.S. flagship Great Guardian, was heavily damaged by the UX. The 707 returned and engaged Red, who was eager to face his rival. After evading attacks, the 707 was hidden in a valley. Red attempted to destroy it by triggering a mudslide, but the 707 barely escaped and became trapped in a water layer within a crater. As it struggled to surface, multiple torpedoes were fired at it.