[Lee Sang-hoon's Korean History] The Mystery of the Two Japanese Expeditions by the Ye Mong Allied Forces

In Early October 1274, 40,000 Troops Departed from Changwon... Victory in Battle Against Japan but Forced to Retreat
Storm Damaged Ships and Soldiers Drowned... The Beginning of Japan's 'Kamikaze' Believed to Be Divine Protection
In 1281, Goryeo's 40,000 and China's 100,000 Expedition... Another Storm Causes 100,000 to Drown or Be Captured as Prisoners

Sanghoon Lee, Professor at the Korea Military Academy

In 1266, the Mongols attempted to summon Japan across the sea. Mongol and Goryeo envoys crossed over to Japan more than ten times. However, Japan refused. The envoys were detained or killed. At that time, the Sambyeolcho Rebellion was ongoing in Goryeo, so Japan was considered a lower priority. In April 1273, the Mongol-Yuan allied forces succeeded in suppressing the Sambyeolcho on Jeju Island. After that, the invasion of Japan resurfaced. The Mongols began securing military provisions through the Tuntian Jinglue Shi (屯田經略使). They demanded the Goryeo government to secure provisions and build warships. In 1274, the Mongol-Han army (蒙漢軍) under the Eastern Expedition Supreme Commander’s Office (東征都元帥府) was organized with 26,000 troops as the main force. Goryeo contributed 8,000 soldiers and 6,700 Chogong (梢工) and Susu (水手) responsible for ship operations. Additionally, 900 warships built by Goryeo were prepared.

On October 3, 1274, about 40,000 Mongol-Yuan allied troops departed from Happo (合浦, present-day Changwon) and headed to Japan. The route connecting Korea and Japan is dotted with islands like stepping stones. The allied forces occupied Tsushima Island (對馬) on October 6 and Iki Island (壹岐) on October 14. Then, on October 20, they landed at Hakata (博多, present-day Fukuoka) in northern Kyushu (九州) and engaged in full-scale combat with Japanese forces. In this battle, the Japanese army was defeated and retreated. Goryeo general Kim Bang-gyeong (金方慶) advocated continuing the fight after landing. However, Mongol commander Hundo ordered a retreat to the anchored ships. Ultimately, on the dawn of October 21, a great storm severely damaged the Mongol-Yuan fleet. Many soldiers drowned during this event. This is the origin of the 'Kamikaze (神風)', the divine wind believed to have protected Japan.

In Japan, it has been understood that the Mongol-Yuan allied forces were defeated thanks to the Kamikaze. However, some argue that the date of October 20 does not align seasonally. According to Volume 208 of the Yuan Shi (元史), it was recorded that "the official army was disorganized and had exhausted all their arrows." It is presumed that the Mongol-Yuan forces decided to withdraw due to depletion of food and arrows and then encountered the storm.

In summary, before the natural phenomenon of the storm, the Mongol-Yuan allied forces had already lost combat effectiveness. The successful defense by the Japanese army defeated the allied forces. At that time, the Mongol-Yuan allied forces numbered about 40,000, and the Japanese army about 20,000. Although the allied forces were the expeditionary army, questions remain as to whether they were really pushed back so much by the Japanese forces.

It is said that food and arrows were depleted, but expeditionary armies at that time carried at least three months’ worth of provisions. During the second Mongol invasion, Kim Bang-gyeong mentioned, "We brought three months’ worth of provisions according to the imperial decree." The expedition began on October 3, and the storm occurred on October 20. It is hard to believe that supplies were exhausted in less than a month. It is more natural to assume that the ships carrying supplies were lost due to the storm. Consequently, the Mongol-Yuan allied forces could not hold out and had to retreat.

The Mongol-Yuan allied forces departed Happo on October 3 and landed in Kyushu on October 20. Considering the length of the route, their advance speed seems somewhat slow. The route from Geoje Island to Tsushima Island, Iki Island, and Kyushu is still known for unpredictable weather. It is possible that they suffered considerable losses during the voyage.

Another problem was the lack of stable port facilities or estuaries that the allied forces could use. If the allied forces had properly unloaded supplies and established a foothold after their victory, history might have been different.

In 1279, the Mongols completely conquered the Southern Song (南宋). Once they had sufficient resources, they accelerated preparations for another invasion of Japan. The Mongols planned to attack Japan at once using the military forces from the Southern Song region and Goryeo. King Chungnyeol of Goryeo was appointed Prime Minister of the Eastern Expedition Secretariat (征東行中書省) and prepared for the expedition again. They needed to mobilize 10,000 Goryeo troops, 15,000 Chogong and Susu, 900 warships, and 110,000 seok of provisions.

In May 1281, the Mongol emperor ordered the second invasion of Japan. About 40,000 troops of the Eastern Route Army (東路軍) departed from Goryeo on 900 ships and headed to Japan first. They passed Tsushima Island and established a base on Iki Island. They then attempted to attack the Hakata area but were unsuccessful. Japan had strengthened defenses in this area after the first Mongol invasion. About 40,000 Japanese troops were already defending. The Mongol-Yuan allied forces had no choice but to retreat to Iki Island.

About 100,000 troops of the Jiangnan Army (江南軍) from southern China boarded 3,500 ships and headed to Japan. The Jiangnan Army was led by Fan Wenhu (范文虎), a general from the Southern Song who had surrendered to the Mongols. An advance party of 300 ships arrived first at Tsushima Island, and the main force of 3,200 ships reached Hirado Island (平戶). Hirado Island is located southwest of Iki Island. Tsushima Island lies north of Iki Island, and Hakata is southeast of Iki Island.

Finally, the Eastern Route Army and Jiangnan Army joined forces at Hirado Island. Most of the expeditionary forces then moved to Takashima Island (鷹島) to prepare for landing on the Kyushu mainland. Takashima Island is east of Hirado Island and south of Iki Island. To go from Hirado Island to Hakata, one must pass Takashima Island and proceed further east. However, as in the first invasion, they encountered another storm. About 100,000 soldiers drowned or were captured by Japanese forces.

The Jiangnan Army undertook a long voyage without proper war preparations. The Southern Song generals surrendered before fighting. Most of the Jiangnan Army consisted of Southern Song troops who had surrendered to the Mongols and even brought farming tools for long-term occupation in Japan. It is difficult to consider the Jiangnan Army as elite troops.

Most of the Jiangnan Army was annihilated, and the Goryeo army suffered about 7,000 casualties. The Goryeo-sa (高麗史) records, "The Eastern Expedition Goryeo army numbered 9,960, and the Chogong and Susu numbered 17,029, of whom 19,397 survived."

At this time, Goryeo’s sturdy ships were not damaged, so losses were minimal. In contrast, hastily built Jiangnan ships sank or were damaged more than half. The Goryeo-sa states, "Jiangnan ships are large but break easily upon collision." In other words, Goryeo’s ships were smaller but more durable.

One question arises here. If 40,000 Eastern Route Army troops boarded 900 ships, the number of troops per ship was about 44 to 45. If 100,000 Jiangnan Army troops boarded 3,500 ships, the number of troops per ship was about 28 to 29. Even if the Jiangnan Army carried more supplies due to the long voyage, the number of troops per ship was clearly much lower than that of the Eastern Route Army. The Jiangnan ships were larger but carried fewer troops. The initial plan was to deploy 100,000 troops. However, it is questionable whether all of them were actually mobilized and safely arrived in Japan. It is highly possible that the reinforcements had not yet arrived when the allied forces moved to Takashima Island.

The main force of the Mongol-Yuan allied army moved to Takashima Island, while a general named Jang Hui (張禧) remained stationed on Hirado Island. He built fortifications and anchored ships spaced 50 paces apart to prepare for the storm. Even if not exactly 50 paces, it was clearly to prevent collisions between ships.

As a result, Jang Hui’s troops stationed on Hirado Island were not damaged by the storm. Jang Hui led 4,000 men. They may have both restrained Japanese forces and welcomed reinforcements. In any case, Jang Hui was unharmed by the Kamikaze and was later able to provide ships to Fan Wenhu of the Jiangnan Army.

Another question arises. Takashima Island is only about 13 km long and 5 km wide. Not all 4,000 expeditionary ships could have anchored there. The area is too small for all 100,000 troops to have landed.

The movements of the Mongol-Yuan allied forces are full of questions. Historical records are limited. Underwater excavation was conducted around Takashima Island in 1992, but it is still insufficient to fully understand the reality. We hope for progress in underwater archaeological discoveries related to the Mongol-Yuan allied forces in Japan.

Lee Sang-hoon, Professor of Military History, Korea Military Academy