Turtle ships participated in the war against Japanese naval forces supporting Toyotomi Hideyoshi's attempts to conquer Korea from 1592 to 1598. Korean Admiral Yi Sun-sin, who won all battles against Japanese Navy, is credited with designing the improved turtle ship. His turtle ships were equipped with at least five different types of cannons and greatly contributed to winning 16 times from 16 battles against the Japanese Navy until they were destroyed in the Battle of Chilcheollyang since their first appearance in the Battle of Sacheon (1592). Their most distinguishable feature was a dragon-shaped head at the bow (front) that could launch cannon fire or flames from the mouth. Each was also equipped with a fully covered deck to protect against arrow fire, musket-shots, and incendiary weapons. The deck was covered with iron spikes to discourage the enemy from attempting to board the ship.