Turtle ships are the most famous part of Admiral Yi's fleet; however, he never deployed more than five in any one battle. The Joseon Dynasty used cannons as its primary offensive naval weapon. Historically, they had often used guns and cannons against Japanese pirates as early as the 1390s. The Joseon navy did not implement the ship-boarding strategy that the Japanese navy did, so it was imperative that their warships "stand off" from Japanese vessels. Admiral Yi made it a strategic priority to avoid hand-to-hand combat, in which the Japanese navy specialized. The turtle ship was developed to support his tactic against Japanese fleets.