Geobukseon ("Turtle Ship") of Great Admiral Yi Sun-shin – the combat ship that helped to save Korea
Used by Admiral Yi Sun-shin during the Hideyoshi Invasions in the 16th century, these innovative warships were instrumental in effectively defeating the Japanese invaders.
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-Shin is credited with designing the ship. His turtle ships were equipped with at least five different types of cannons. Their most distinguishable feature was a dragon-shaped head at the bow 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 enemy men from attempting to board the ship.
A dragon head mounted on the bow of the vessel emitted foggy sulfur gas to effectively throw the enemy fleet into disarray, as well as to hide the ship itself as it approached and maneuvered among enemy ships. The dragon head housed a cannon inside as well. The dragon head, both fuming fire and shell, served as a form of psychological warfare in shocking Japanese soldiers.
The question of whether the "turtle ship" was really an armored battleship was first raised in the 1880s and remains unsolved today. The affirmative argument is mostly asserted by Western scholars based on Japanese records. There are many Japanese documents from the Imjin Invasions that note "the enemy (Joseon) has ships that are covered in iron that we cannot break with our cannons."
http://www.antiquealive.com/Blogs/Geobukseon_Turtle_Ship.html
https://en.wikipedia.org/wiki/Turtle_ship