The Battle of the Sea of Japan was a conflict that occurred in 20th century, which was waged during Earth's Eugenics Wars. It was considered the turning point in the conflict, as it saw much of Khan Singh's military force being destroyed, and marked the beginning of the end of his superrace. After the battle, the Great Khanate splintered into a dozen factions which started fighting one another, which eventually led to their leaders being hunted down by the planet's governments.
Peter Linde Offenhouse was a pilot during the engagement, and was stationed on the naval ship USS Enterprise when she was blown up in the Sea of Japan, two years after his father was placed in suspended animation. Despite his death, his actions helped in saving the human race from the tyranny of the Augments. (TNG novel: Debtors' Planet)