It was the first his battle against Japanese fleet during Imjin war period. He sent spy ships to eastern sea off Busan port. He didn’t depart his naval base until he confirmed Japanese fleet’s scale and tactics. On May 7, his fleet and Won gyun’s fleet departed together and sailed to okpo port. Japanese fleet disembarked from their ships and was plundering villages near by okpo port. Japanese embarked quickly after they found Joseon fleet. Admiral Yi waited until all Japanese boarded and ordered to discharge guns. His fleet was in a formation of Iljajin which ships position a line east-to-west. He didn’t use boarding tactics, which were very common at that time. He ordered to bombard guns against Japanese ships. This battle became first victory of Joseon while Joseon army couldn’t attain in land.