Admiral
A navy from this historical state sank 31 ships, without losing a single vessel, after recognizing that a current was alternating every three hours. This kingdom invented a cart which fired 200 fire-arrows simultaneously at the enemy, as well as a double-decked ship called the pan·okseon. Boats used by this historical state were armored with iron spikes and released smoke from the bow. Admiral (*) Yi popularized its turtle ships. This nation's Joseon dynasty defeated Hideyoshi Toyotomi, but Japan occupied it from 1910 till 1945. For 10 points, name this kingdom which was separated during a 50s war on an Asian peninsula.
A navy from this historical state sank 31 ships, without losing a single vessel, after recognizing that a current was alternating every three hours.
Kingdom of Korea [or Choseon or Joseon Dynasties until it is read]