The Japanese invasion of Korea began with the arrival of 400 transports bearing 18,700 men under the command of
Konishi Yukinaga on 23 May 1592 for the
Siege of Busanjin. Over the next several weeks, the Japanese fleet ferried
Toyotomi Hideyoshi's invasion force of 158,000 men to the Busan area, and the Japanese armies had advanced rapidly northward, and had seized the Korean capital of
Hanseong by 16 June. As the Japanese now prepared to advance further north, logistics became an issue, and Japanese transports began exploring further up the west coast of the Korean peninsula as it was not practical to carry large amounts of supplies overland given the rough terrain and poor state of the roads. At the time of the invasion, the Korean naval forces were divided into regional commands. Panicking after the fall of Busan to the Japanese, Gyeongsang Left Navy Commander Bak Hong ordered his weapons and stores destroyed, and scuttled his fleet of 100 warships without giving combat. Likewise, after the
fall of Dongnae, Gyeongsang Right Navy Commander
Wŏn Kyun attempted to withdraw his ships to
Hansando but mistook a bunch of fishing ships for the Japanese fleet. He proceeded to destroy his weapons and stores, and to scuttle his fleet. He was dissuaded from deserting his command by his subordinates, by which time he had only four vessels remaining. Wŏn Kyun called on Yi Sun-sin for assistance; however, as commander of the Cholla Left Navy, he was not allowed to leave his region without permission from his superiors. Yi also had a number of other reasons to delay. He needed to acquire charts of the rocky coastal waters of
Gyeongsang Province for his fleet to navigate safely, and he was also uncertain of the discipline of the men under his command and was forced to execute deserters to set an example, including on 12 June, the day Hanseong fell to the Japanese. Yi Sun-sin had hoped to combine his forces with that of Cholla Right Navy Commander
Yi Ŏkki; however, when orders came from the capital, he was ordered to combine with the now non-existent forces of Wŏn Kyun instead. With Wŏn Kyun's remaining four vessels, Yi Sun-sin had 39 warships under his command (24 large and 15 smaller
hyeupson) and 46 smaller open boats. When Yi Sun-sin and Wŏn Kyun arrived near
Geojedo on 16 June, a scouting vessel alerted them to the presence of Japanese ships anchored at the port of
Okpo. ==Battle==