The first recorded Wako activity occurred in 1223 when Kumju was raided. The first stage of these raids were minor in scale and occurred on sporadic intervals. Then the presence of Mongol troops in
The initial attempts by the Korean military to combat the Wako pirates ended in disaster. In 1351, troops were placed aboard ships to fight the pirates. However, the military commanders did not engage the Japanese. Instead, they withdrew when the pirate ships were spotted or avoided closing in to fight. By this time, the Wako pirates had complete maritime supremacy in the Korean waters.
The Wako raids began to have devastating impact on
U Hyon-bo, a court admonishing officer, in 1373 admonished the king eloquently in his memorial. Excerpts as translated by Benjamin Hazard in his Ph. D. dissertation is as follows:
Critics have said that, because the [Japanese] pirates are good sailors, we should not meet them in naval warfare. If we build ships, this would double the burden on the people. This is not so. Pirates cannot be attacked from land. That condition is very clear. Moreover, in the driving off of pirates and preventing violence, our basic desire is on behalf of the people. Can critics think of minor distress of the people and give great grief to the country? Now, along the Tong and So River defenses are placed. When the pirates come sailing on the sea at will, our army stands on the shore and can do nothing more than look on with folded arms, even with a million picked troops. When it is a matter of water, what can they do? We ought to build ships, carefully equipped and armed [author's emphasis], and following the currents in long columns block their principle routes.
Starting in that same year, 1373, the Koreans finally seemed serious about combating the Wako and began to build up the Korean Navy. Ch'oe Yong, a leading army general, began to solicit for new warships. He wanted to increase the navy by 2000 warships and put all of the Korean military on them to fight against the Wako pirates. In October 1373, a demonstration was held for the King on the newly constructed warships with their fire arrows and fire tubes. However, no further progress with the naval armaments was made until 1377 when Ch'oe Mu-son gave his famous firepower demonstration of his new cannons.
In 1380, the cannon is finally used in naval combat against the Wako on the
The invention of the kobukson has often been attributed to Admiral Yi. His biography states he "invented" it, but it is more likely Admiral Yi took an existing design and modified it for his own special use. One reason is the term "kobukson" can be found in Korean annals early as 1414 when King T'aejong inspected this new type of war vessel. Given the surge in naval development from 1377 to combat the Wako raids, it is not surprising to find the Koreans experimenting with warships. Also in 1389, Yi Song-gye had assumed control of
The aggressiveness shown by King T'aejong toward sea-fighting makes it appear the kobukson was designed as an attack ship. Certainly by the time Admiral Yi modified it with new advanced cannons and iron spikes on the roof, it became an offensive weapon. In certain aspects, Admiral Yi used the kobukson as if it was the sea version of the ancient chariot. Sun Tzu's The Art of War makes frequent reference to the chariot and how to employ it in battle. Admiral Yi as a student of military classics must have realized the similarities, because he uses the kobukson as his main attack weapon in the Imjin War.