Battle of Kōan The , 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 .