It is generally assumed that the age of ironclad warships began in the 1850s. The fact, however, is that the ironclad was introduced more than 250 years earlier.
In 1592, Japan invaded Korea, which was on the verge of defeat until Korean admiral Yi Sun-Sin stepped into the breach with a fleet of vessels he had helped design. He called them "turtle ships". These were the world's first ironclads, which enabled Korea to drive off the Japanese invaders.
In 1598, during a second Japanese invasion, Yi achieved an even bigger victory, destroying more than 200 Japanese ships and killing some 40,000 Japanese sailors and soldiers. He was killed in that battle. His last words were: "Do not weep, do not announce my death. Beat the drum, blow the trumpet, wave the flag for advance."
裝甲戰船，一般認為始於一八五零年代。其實，在此二百五十多年前，甲船已經出現。
一五九二年，日本犯朝鮮，朝鮮不敵，岌岌可危，幸得海軍上將李舜臣奮起，力挽狂瀾。李舜臣參與設計了一隊戰船，名之為龜甲船，是甲船的始祖。朝鮮仗這些甲船擊退日本侵畧者。
一五九八年，日本再犯朝鮮，李舜臣迎敵，勝利更加輝煌，摧毀日本戰船二百餘艘，剿殺日本水手、將士約四萬人，但他也死於這場戰役，臨終時說：「且莫哭泣，且勿發喪。擊鼓吹號，揚旗前進。」