난중일기(1977) / A War Diary (Nanjung-ilgi)

Admiral Yi Sun-sin builds his turtle ships ahead of the Japanese invasion, wins at Okpo and Hansan, is thrown in prison by political rivals anyway, and comes back with a dozen ships to win his largest battle yet. The film closes on his final stand at Noryang, tracking a naval campaign still taught in Korean schools as a case study in holding a line against impossible odds.

Why it's free: Free on the Korean Film Archive's own channel; the national archive publishes the restorations it holds the rights to.