Geobukseon & Yi Sun-Shin

 His service in the government & his service in the war as a commoner
In 1576, at the age of 32, he passed the Siknyeonmugwa (The military service examination: a formal government exam that was given every three years). In the Joseon Dynasty, a person at the age of 32 was not regarded as young as today. Since early marriage was in fashion at that time, most people married in their early teens.
Because of his maturity he had great skill in archery and tactics, passed the exam for military service, and never gave upon his will to become a soldier who combines both literary and martial arts.
He was assigned to Donggubibogwan, Hamgyeong-do as his first civil service assignment. He became Josanbomanho in 1586 after serving in various posts like Hanseong training camp servant, and in the following year he held that office along with the post of Nokdoondodunjeongwan. There he was framed up by Yi Il who was a Bukbangsa and was punished by the King to serve in a war as a commoner (his first service in a war as a commoner without a governmental post). But in January 1589, he was reinstated after making a contribution to occupy Sijeon village in a battle with Yeojin.
In February 1589, he was appointed by Lee Gwang who was the governor of Cholla-do, and in November he became Seonjeongwan (messenger, an officer responsible for receipts and payments), and in December he became the Hyeongam of Jeongeup.
 Invention of Geobukseon and his triumph in Imjin War
He was recommended by Seoye, Ryu Seong Ryong, who knew his ability very well to become Cholla Left Navy admiral in 1591. He maintained the gun quarters and expanded the budget for the military preparedness. Meanwhile, he made efforts to strengthen the training for the demoralized and incompetent navy and beefed up the military capability. In addition he foresaw the large scale invasion of Japanese and prepared for the war, inventing the Geobukseon.
In April 13, 1592, he achieved consecutive and sweeping triumphs in small or large scale battles, winning a sweeping victory in Okpo naval battle, his first naval battle on May 04, in Hansan Naval Battle on July 08 and in Busan Naval Battle on September 01, completely securing the command of the sea and reversing the tide of war.
 Triumph in his second serving in war as a commoner and in Jeongyujaeran
The naval battle came to a lull until the Jeonyujaeran war broke out. He was imprisoned on March 04, 1597 after he was framed by the royal court for his alleged involvement in Yosira espionage case while he was preparing for the war in anticipation of the Japanese invasion. After that, he was imprisoned in many times and was set free on April 01 and started his second service in the war as a commoner. In the meantime, Joseon navy led by Won Gyun of Gyeongsang Right navy was almost completely defeated in the battle of Chilcheonryang in July 16, and Yi Sun Shin was reappointed as the Naval Commander of Three Provinces on July 22.
He received a secret letter from the King to do away with our navy in Yeolruseon of Boseong in August 15. He answered the letter by saying, "We still have 12 ship and I am still alive." And he composed a song of Hansan island, expressing his responsibility and loneliness as a navy commander.
In his remarkable and sweeping victory in the naval battle of Myeongrang, he destroyed 31 enemy ship completely only with 13 ship in September 16 though he faced the enemy ship 10 times as many, which is a world record in the history of naval battle. Subsequently, he achieved a great victory both in naval and land battle as well as in the battle of Haenam Uldolmok, even while he was staying at Baleumdo island(Sinan-gun, Chollanam-do) for a few days, occupying a position.
In February 1598, he relocated his position to Gogeumdo island, and in July he organized the allied fleet with Jin Rin, navy command of Myeong, reinforcing the military capability.
On November 19, he was shot by an enemy bullet and fell at Norayong at the southern sea just before he achieved a sweeping victory in the naval battle of Noryang where he destroyed around 200 enemy ships. He died at the age of 54, leaving his last word,
"Do not tell them that I was killed since the fighting is urgent now."
 Spirit of Admiral Yi Sun Shin
Admiral Yi Sun Shin was a great commander who saved the nation from the imminent collapse of the nation during the Imjin War, encouraging his soldiers who were facing a gigantic number of enemy, by saying "Do not behave recklessly, be carefully and stable like the mountain does not lose any balance", "You will die if you are worried about your life, and if you are not afraid to die, you will live." He was also a good poet and kept a diary called Nanjungilgi(diary kept during the War) which is a valuable historic data. His written reports(report written by local official at the order of king or auditor) is famous for their excellence. He wrote many poems and verses, such as his letter to Lee, Won-Ik who was jechalsa, a governmental official, which was titled ',Sangjechalsa Wangpyeong Lee Gong Wonikseo' and 'the Song of Hansanseom island.
Furthermore, he had a great filial devotion to his parents which seemed obvious in his diary, Nanjungilgi. Admiral Yi Sun Shin set the example for us living in modern times through his loyalty to the nation and patriotism based on his filial devotion, his self-reliant and independent spirit throughout his life to carry out the justice, and his unyielding creativity that remain a great symbol of our race.
 Protective deity of the nation
In 1601 (the 34th year of reign by Seonjo), Chungminsa shrine was set up to commemorate Admiral Yi Sun Shin and a posthumous epithet of Chungmu was granted to him in 1643 (the 21th year of reign by Seonjo). In 1706(the 34th year of reign by Sukjong) granted a shrine named Hyeonchung and Hyeonchungsa shrine was built in Asan where Admiral Yi Sun Shin is buried, encouraging the his loyalty and patriotism. Thus, he was reborn as the Great Admiral Yi Sun Shin, a protective deity of the nation.