■ Na Dae-yong (羅大用:1556-1612)
Na Dae-yong was born in 1556 in the city of Naju in the Jeolla-do province. He and his cousin Na Chi-yong began serving under Yi Sun-sin in 1591, one year prior to the outbreak of the Imjin War. As a lieutenant, and with Yi’s complete confidence, he was given the responsibility of constructing the Geobukseon and other battleships. The Geobukseon was built by remodeling the Panokseon battleship, then Korea’s primary battleship. These battleships were specifically designed for naval battles against Japan, whose navy excelled in on board hand-to-hand combat. The Geobukseon was shielded by a roof covered with iron spikes to prevent enemies from boarding the ship. It played a decisive role in breaking the enemy’s formation by spearheading attacks. The Geobukseon could rampage through the enemy fleet and fire cannons from every direction of the ship. Needless to say, the Geobukseon made an enormous contribution to the Korean Navy’s victories during the Imjin War. Na Dae-yong was not only an excellent shipbuilding engineer, but also a courageous soldier who carried out remarkable operations in many naval battles, including the battles of Okpo, Dangpo and Sacheon. He was wounded by enemy fire at the battle of Sacheon along with Yi Sun-sin. After the war, he continued to study battleships, and developed another ironclad battleship called Changseon, which was densely covered with swords and spears.
■ Eo Yeong-dam (魚泳潭: 1532-1594)
Eo Yeong-dam served as an officer titled Hyeongam in the city of Gwangyang, an area within Yi Sun-sin’s jurisdiction, when the Imjin War broke out in 1592. Since he grew up by the water, he had considerable skills in the operation of ships. He was also particularly knowledgeable of the tides and currents of the seas around the Gyeongsang-do and Jeolla-do provinces, and so served as a tide expert. This ability made a significant contribution to the victories of the Korean Navy during the Imjin War.
Eo Yeong-dam engaged in the operations of many great naval battles, including the battles of Okpo, Hansando, and Busan, until he died of infectious disease in the naval base in Hansando in April, 1594. On April 9, 1594, Admiral Yi Sun-sin wrote in his war diary (Nanjung Ilgi in Korean) that “My defense soldier Eo Yeong-dam died. How can I say how sad I am?” Eo Yeong-dam was an outstanding soldier whom Yi loved and trusted very much.
■ Yu Seong-ryong (柳成龍: 1542-1607)
Yu Seong-ryong served as second state councilor. Upon the outbreak of the Imjin War in 1592, he also took the lead in general military affairs as the minister of war. For all seven years of the war, he played a crucial role in bringing the war to victory by leading all state affairs, including military affairs, administration and diplomacy.
Also, he recognized the ability of General Yi Sun-sin and General Gwon Yul, and raised them to high positions by recommending them to the King before the Imjin War. As he expected, these two generals thoroughly prepared for war, and performed distinguished service during the war in naval and land combat respectively. He had known Yi Sin-sin from childhood, and appreciated his noble character. Whenever Yi went through hardship in his life, Yu would give him special assistance. As a prominent scholar, Yu Seong-ryong left many writings. Among them, Jingbirok (懲毖錄) is famed as a remarkable documentary record of the Imjin War, and was designated in 1969 as National Treasure No. 132. In the opening of the book, he stressed the need to be wary of possible wars by learning from the lessons of the Imjin War.