In 1587, Na dae-yong threw away his government post, and came to his hometown to design the turtle ship. He studied arithmetic, read books about ships, and produced a model of the turtle ship. At that time, there were administrators who were experts in mathematical calculations in big public works, but people who made personal inventions like Na dae-yong should have studied arithmetic alone to apply mathematical calculations on ship. Nevertheless, the design of turtle ship was successful. Na looked up the designs of warships which people had made from the period of the Three States until now. At the moment, Joseon's naval forces' major warship was the
Panokseon. One of the
Panokseon's chief features was a higher upper deck, which hindered enemy boarding attempts and enabled the Korean crews to fire their arrows further. However, the front of the ship was relatively lower, so it could be attacked by enemies. Also, there were no ways to fend off enemy arrows or spears on the upper deck because the soldiers were exposed. During the
Goryeo period, the naval force used Gwaseon () to defeat the Japanese raiders. Gwaseon could fend off enemies by fixing knives in the ship's flanks. Additionally, they featured
iron rams to attack enemy ships in front of the Gwaseon. The Byeolmaengseon () was another type of warship that Na concerned himself with. A Byeolmaengseon's top deck was completely covered, and the soldiers were posted inside of the ship. Na Dae-yong designed the turtle ship as a combination of the best features of the Gwaseon, the Byeolmaengseon, and the Panokseon. Its hull is likely based on the
Panokseon, but the top deck was completely covered like with the Byeolmaengseon, and the spikes on its roof came from the Gwaseon. == Related historical documents ==