Geobukseon & Yi Sun-Shin

The peculiar geographical condition of the southeastern coast of Korea which has many complex, large and small islands, wide mud flats as well as large difference between the ebb and flow, made it impossible
for "submerged & low draft ship(Chimjeo ship)", which was the common type of the ship during Joseon Dynasty, to navigate forward when the stem of ship is turned because such type of ship draws deep, and to make it worse while the tide is low, it was very easily traced or chased by enemy ships.

The Joseon Navy used large, medium and small ships until the early 16th century, and the, small type ship dominated the rest.
  But, the ships became larger starting from the Saryangjin War (the 39th year of Jungjong, 1544) and Ulmyo War(Myongjong 10th year, 1555), and from that time, stronger and agile navy ship was required to fight against the bigger Japanese navy ships which were reinforced with external plate. Wooden-plated ships (Pan-ok ship) were the solution. Wood-plated ships which were 'horizontal low draft ships' had free movement because it did not draw deep and had small turning radius when the ship is turned. In addition, it was equipped with outfits on the left and right side of the deck, as well as on the decorated deck side, which elevated the level of the ship body, giving an absolute advantage to cope with the basic boarding tactics of the Japanese navy.
But no record is found that indicates when the Geobukseon was built.
Head of Cholla Left navy, Yi Sun Shin and his subordinate generals, including officers who had to fight against the enemy with a few ships, needed desperately a powerful navy ship in order to defeat the enemy firmly in naval battles, blocking the rain of arrows and frustrating the boarding tactics of enemy, and from this necessity, officer Nah, Dae-Yong and others improved wood-plated ship, and added iron-clad, dragon head, sails and cannons, and in this way, our proud Geobukseon was invented.