Upon the outbreak of the Imjin war, Yi served as a Central Commandant (중위장; 中衛將) in the Admiral Yi’s first campaign. Since then, he had always been at the vanguard as Front Commandant (전부장; 前部將). He led the vanguard and lured the Japanese troops. After the Battle of Hansando Admiral Yi Sun-sin, who felt sorry that his contribution was not recognized, suggested to the government his promotion and he was eventually promoted to Jeolchung (절충; 折衝), third senior rank and appointed the Naval Commander of Chungcheong Province. However, he was dismissed due to the strict application of the penal code and demoted to the Associate Commander of Goryang. In 1597, when the Japanese second invasion broke out, he was appointed as the Naval Commander of Right Gyeongsang Province to replace Bae Seol who fled from the Battle of Chilcheollyang. Later, he served as a Central Commandant again under Admiral Yi Sun-sin. When Yi Sun-sin was killed by enemy bullets in the Battle of Noryang, he commanded Joseon's naval forces.