Japanese employed field artillery only where strategically advantageous in both siege and field warfare situations, often using captured pieces where available. The Koreans actively deployed their cavalry divisions in action. But the terrain was often mountainous, which was not generally suitable for cavalry, the farmland tended to have many ditches, and it was often barren and lacked grass essential for feeding the horses. In addition, Japanese use of the arquebus at long range and in concentrated volleys negated any possibility of effective cavalry tactics. Korean cavalrymen's primary weapons were bows, with swords and lances holding only subsidiary positions. Most cavalry action for the Koreans took place in the Battle of Chungju at the beginning of the war, where they were outnumbered and wiped out by Japanese infantry. Although the Japanese divisions also fielded cavalry they usually dismounted when engaged in action, acting more as mounted infantry. While specialized firearms were used on horseback, most cavalrymen preferred the conventional yari (spear), but its use was limited by the increasing use of firearms by the Koreans and Chinese. Naval power In contrast to the Japanese advantages on land, the Koreans possessed an advantage at sea. Because of advanced artillery and shipbuilding technology, along with an extensive naval history against Japanese pirates, the Korean navies fielded highly advanced and formidable ships. By the time of the Japanese invasion, Korea employed the panokseon, a powerful galley-type ship armed with cannon that outranged most Japanese vessels. The Korean navy used this naval superiority to disrupt the Japanese logistical network off the west coast of the Korean Peninsula. This advantage, however, did not affect Japan's ability to continuously reinforce its armies through the supply route from Tsushima in Japan to Busan in Korea, especially once Korean naval bases in the immediate area were neutralized by Japanese ground forces. The Korean navy led by Yi Sun-sin would withdraw and re-base in the northern border of Jeolla Province. While not able to entirely prevent reinforcement, the Korean navy continued to harass and inflict losses on the Japanese supply fleets throughout the duration of the war. As virtually all Japanese ships in the first phase of the war lacked cannon artillery, Korean ships outranged and bombarded Japanese ships with impunity outside the range of the Japanese muskets, arrows, and catapults. When the Japanese attempted to outfit cannon to their ships, their lightweight ship design prohibited using more than a