Yi made an outstanding contribution to naval military strategy with the redesign of the Turtle ship. Actually, his use of the Turtle ship had a parallel on the other side of the globe. At about the same time, Sir Francis Drake used his fire ships to disorient and overwhelm the Spanish Armada. Yi used the Turtle ship as a fire ship, except the Turtle ship survived to fight another day while Drake's fire ships burned in the attack. Still, both Yi's and Drake's strategies had the same effect; disoriented a superior naval force and annihilating them.
Yi not only faced a determined foe in the Japanese navy and army, he had far fewer ships then his enemy. Koreans, historically, are not a sailing people. They had conducted little of their trade by water and had little experience with the sea, other than fishing. He redesigned the Turtle ship, adding more protection for the Korean sailors from Japanese arrows.
Although the Turtle ship is not technically an iron clad in the same way that the Monitor and the Merrimack would be about three centuries later, and it could not submerge, the Turtle ship represents an enormous innovation in naval architecture and ship building. Yi redesigned the Turtle ship to strike terror into the hearts of his opponents with fire through the dragons mouth, delivery devastating canon fire power, and survive to attack repeatedly. He created a ship that carried enormous cannon power. That enable Yi to fight with the remnants of a defeated navy, leading the few ships in his command to defeat the Japanese fleets again.
East Asia has provided the world with a number of firsts, including gun powder, movable type, and the "iron-clad" ship. Although the Turtle ship disappeared from the scene of Korean naval strategy soon after Admiral Yi's deployment, the innovations developed in the Turtle ship would find rebirth again in the industrial age of the nineteenth century.