The most noted hero of the invasion was Admiral Yi Sun Sin for he was the man who played the greatest part in defeating the Japanese. A man of great ingenuity, he developed the kobukson "turtle ship," probably the first iron clad battleship in history. The galley was decked over with iron clad panels to protect the rowers. The ship was so named because it was armed with a large, iron, ramming device in the shape of a turtle head. These ships were almost impervious to any weapons that the Japanese could muster and so the ships were able to sink a large number of Japanese ships.  To illustrate the effectiveness of these ships and the brilliant tactics of Admiral Yi, we need only look at one of the many battles he won. On September 16, 1597, he led 12 turtle ships against 133 Japanese ships in the Myongnyang Straits. The Koreans sank 31 enemy ships and sent the others fleeing in this victory. The Japanese were forced to give up their invasion (after seven years), but the struggle had devastated Korea. Whole towns had been looted and destroyed, crops were ruined, and famine and disease swept the country. After the war, the royal government revived strong defense measures by strengthening military training and martial arts practice.

Unfortunately, Admiral Yi never got to see the rewards of his heroic efforts and brilliant strategy. On November 19, 1598, Admiral Yi was shot during the final battle of the war. He commanded that his body be hid by a shield so his enemies could not see that he had fallen. To his oldest son, he whispered, "Do not weep, do not announce my death. Beat the drum, blow the trumpet, wave the flag for advance. We are still fighting. Finish the enemy to the last one." He was 54 years old when he died.

Admiral Yi  kept a careful record of daily events in a diary, and it is from these entries, along with the reports he sent to the throne during the war, that much about the man has been learned. These works have been published in English as Nanjung Ilgi: War Diary of Admiral Yi Sun-sin, and Imjin Changch'o: Admiral Yi Sun-sin's Memorials to Court. (Translated by HA Tae-hung, Yonsei University Press)

In these writings, we can find many useful lessons for today. From Admiral Yi's writings, we may infer that a warrior must master three roads, four obligations, five skills, and ten keys to security.

• The three roads are knowledge of the world; understanding of things as they are; and wisdom toward humanity.
• The four obligations are to provide national security with minimal cost; to lead others unselfishly; to suffer adversity without fear; to offer solutions without laying blame.
• The five skills are to be flexible without weakness; to be strong without arrogance; to be kind without vulnerability; to be trusting without naiveté; and to have invincible courage.
• The ten keys to security are purity of purpose, sound strategy, integrity, clarity, lack of covetousness, lack of addiction, a reserved tongue, assertiveness without aggression, being firm and fair, and patience."

Besides being remembered as a tactical genius, Admiral Yi is also remembered as a man of personal integrity. His posthumous title, Ch'ungmu-kong (Lord of Loyalty and Chivalry) is used in Korea's third highest military honor, the Order of Ch'ungmu.

He believed in three essentials for the warrior: humility, discernment, and courage. He embodied all of them, and lived with integrity throughout his life. When Admiral Son Ko-i died in 1598, a letter was found among his possessions. It was from Admiral Yi Sun-shin, and in it he wrote, "My life is simple, my food is plain, and my quarters are uncluttered. In all things, I have sought clarity. I face the troubles and problems of life and death willingly. Virtue, integrity and courage are my priorities. I can be approached, but never pushed; befriended but never coerced; killed but never shamed."

Admiral Yi Sun-shin is truly one of the great warriors of the past, and his legacy and teachings are a blueprint for success for any modern martial artist and warrior. His patriotism and integrity can be a role model for all. There is a statue of Admiral Yi Sun-shin in the middle of Sejongno in downtown Seoul, next to the Kyobo building.

The Manchus invaded Korea in 1627 AD. The invasion was not welcomed but at least it left the country relatively independent of China, who had exacted tribute from the people and kept the Korean government weak.

From the late 17th to the early 19^th century, Korea began a period of isolation, closing her borders to all foreigners in an attempt to secure some peace. Korea became known as the "Hermit Nation" because it turned away foreigners, particularly the Europeans who were expanding their own empires during this time. Toward the end of the 19^th century, Korea set up relations with many western nations in an effort to offset Japanese influence.

Treatises had been written on the most effective fighting techniques, defining them as sets. The first of them was Mooyae Chebo, written in 1599 AD, which included sets of pole techniques (used by Buddhist monks in Korea), sword and shield techniques (using "broom of wolf's tail"), long spear, trident, and long-blade sword. A second treatise, Mooyae Singbo, created about fifty years after the Manchus invasion, included bare-hand combat, exercises with Japanese and Korean swords, spear, military flail, and different blades with a long shaft. However, the greatest Korean book on the martial arts was the Muyedobo-tongji.