Yi was born in Geoncheon-dong, Seoul on March 8, 1545. Because his family was poor, he moved to and grew up in his mother's hometown, Asan, in Chungcheongnam province. He became a warrior at the late age of 32, after failing the exam at the age of 28. When he arrived Jeolla-do province as the navy commander of western part of Jeolla-do province in 1591, he predicted the war with Japan. He disciplined the navy tightly and made the turtle ship, which had at least five different types of cannon and had a fully covered deck with iron spikes to shield from cannon fire and attempt to board the ship, for preparation of the war.
On April 13, 1592, the Imjin War broke out just as Yi had foreseen. Joseon was not prepared for war. Japan occupied nearly all of Korea. Yi had already prepared for war, so he led his navy to victory in every battle he fought during seven years of war with the Japanese. In the battle of Hansan, using crane wing formation he captured and sank fifty nine of the seventy-three Japanese ships. In the battle of Myeongnyang, he defeated 333 enemy ships with 13 ships his own. This victory has regarded as one of the miracle victories of the world.
Through his victories, Joseon dynasty prohibited the Japanese warlord Toyotomi Hideyoshi from governing Joseon. However Yi Sun-sin was killed by enemy fire during the last battle of the war, Noryang, in 1592.