Battle of Kōan

The Battle of Kōan (弘安の役), also known as the Second Battle of Hakata Bay, was the second attempt by the Yuan Dynasty founded by the Mongols to invade Japan; they had failed seven years earlier, in the Battle of Bun'ei. In the summer of 1281 they gathered two invasion forces and invaded. After inconclusive fighting the invasion fleet was destroyed by a storm and the Yuan withdrew; the Japanese called the storm which chased away their invaders kamikaze ("divine wind"), a prestigious name later used in the Second World War for aerial suicide attacks.

Background
After the failed first invasion by the Yuan navy, the Japanese made many defense preparations. Many forts were constructed along the coast line. Samurai further trained, perfecting their swordsmanship.

In early 1280 Kublai Khan planned another invasion of Japan and ordered his shipbuilders to rebuild the whole fleet within a year. In the short time available many of the ships were poorly made; many were flat-bottomed river boats requisitioned by the Emperor.

Battle
By June 1281, 900 Yuan ships were gathered in Korea; the force was called the Eastern Route Army. They were crewed by 17,000 sailors, and transported 10,000 Korean soldiers and 15,000 Mongols and Chinese. The Southern Route Army, meanwhile, was assembled just south of the Yangtze River, in China. It is said to have consisted of 100,000 men on 3,500 ships. As before, Iki and Tsushima islands fell quickly under the great numbers and battle prowess of the Yuan forces.

The Eastern Route Army arrived at Hakata Bay on June 21, and decided to proceed with the invasion without waiting for the larger Southern force which had still not left China. They were a short distance to the north and east of where their force had landed in 1274, and were in fact beyond the walls and defenses constructed by the Japanese. The samurai responded quickly, assaulting the invaders with waves of defenders, denying them the beachhead.

At night small boats carried small bands of samurai into the Yuan fleet in the bay. Under cover of darkness they boarded enemy ships, killed as many as they could, and withdrew before dawn. This harassing tactic led the Yuan forces to retreat to Tsushima, where they would wait for their Southern Route Army. However, over the course of the next several weeks, 3,000 men were killed in close quarters combat in the hot weather. Yuan forces never gained a beachhead.

The first of the Southern force ships arrived on July 16, and by August 12 the two fleets were ready to attack Japan. On August 15 a major tempest struck the Tsushima Straits, lasting two full days and destroying most of the Yuan fleet. Contemporary Japanese accounts indicate that over 4,000 ships were destroyed in the storm; 80 percent of the Yuan soldiers either drowned or were killed by samurai on the beaches. The loss of ships was so great that "a person could walk across from one point of land to another on a mass of wreckage".

Aftermath
Kublai Khan began to gather forces to prepare for a third invasion attempt in 1284, but ultimately was distracted by events in Southeast and Central Asia, and no third attempt was ever made.