By 1274, Kublai Khan — grandson of Genghis Khan and the Mongol emperor who would within a few years complete the conquest of Southern Song China — had been corresponding with the rulers of medieval Japan for six years. The correspondence was one-sided. Kublai had written six letters demanding Japanese submission to Mongol overlordship; the Hōjō regents of the Kamakura shogunate had not answered any of them, executed two of the Mongol envoys, and ignored the rest. The two states had no diplomatic relations and almost no commercial contact. Kublai decided to invade.
The Mongol military system that had conquered most of Eurasia was a land army. The Yuan court at Khanbaliq (modern Beijing) had no significant blue-water naval tradition and no real institutional knowledge of the East China Sea. The invasion fleet would have to be built and crewed by the recently conquered Goryeo Korea, which had military shipbuilding capacity and which Kublai had spent the previous decade subordinating into a client kingdom. Kublai gave the order to begin shipbuilding in early 1274. The 900-ship fleet was completed at the southern Korean port of Masan by autumn.
The first invasion
The Mongol-Korean fleet sailed on 3 October 1274 with approximately 25,000 troops — substantially Mongol cavalry under the command of Hindu Khan, supplemented by Korean and northern Chinese auxiliaries under Hong Tagu and Kim Bang-gyeong. The route ran approximately three hundred kilometres south-southeast across the Tsushima Strait. The fleet reached the small island of Tsushima on 5 October and overwhelmed its garrison of approximately 200 samurai within a day. The Mongols spent the following month systematically reducing the smaller islands of Iki and Hirado.
On 19 November 1274 the main Mongol force landed at Hakata Bay on the north coast of Kyushu — the strategic point of arrival on the Japanese main island. The samurai forces assembled by the Hōjō regency were approximately 6,000 and were tactically unprepared for the Mongol approach to combat. Japanese military practice at the time was based on individual mounted-archer engagement at the unit-of-clan level; the Mongols fought as coordinated units of mass infantry and cavalry, used bows shot in volleys rather than as individual aimed fire, employed primitive bombs and incendiaries (one Mongol device described by Japanese sources sounds substantially like an early Chinese firework or rocket), and were generally indifferent to the Japanese formal challenges to single combat that opened conventional samurai engagement.
The Battle of Hakata Bay was a tactical Mongol victory. By evening of 19 November the Japanese forces had withdrawn to a defensive position approximately seven kilometres inland at Mizuki. The expedition commander Hindu Khan, however, ordered his force back onto the ships overnight to consolidate the day’s advance — a decision the surviving Mongol sources do not quite explain, but possibly motivated by injury rates among the senior Mongol officers and reports of additional Japanese contingents en route.
The decision was catastrophic. A typhoon struck the Tsushima Strait that night. The Mongol-Korean fleet was destroyed at anchor. Modern weather-historical reconstruction suggests winds of approximately 35 metres per second and substantial wave heights. The Korean records report approximately 200 ships sunk and approximately 13,500 men drowned. The surviving fleet limped back to Korea over the following week. The Mongol invasion of 1274 had lasted less than 24 hours of actual land combat. The samurai claimed victory.
The defensive wall
The Hōjō regents took the 1274 invasion seriously. The shogunate ordered the construction of a continuous stone defensive wall along the relevant Kyushu coast, designed to prevent any future Mongol landing at Hakata. The wall was approximately 20 kilometres long, two metres high, three metres thick at the base, and built mostly between 1276 and 1281 by impressed labour and conscripted samurai resources. Substantial sections still survive and are visible as low ridges of mortared stone along the modern Kyushu coast.
The shogunate also requisitioned standing forces from across western Japan for permanent garrison at Hakata. The fiscal cost was severe — the samurai class who provided the garrison were not compensated with new fiefs (there were no new fiefs to be had, since the invasion had been repelled rather than the invader’s territory conquered) and emerged from the decade’s mobilization significantly impoverished. The political-economic strain on the Kamakura shogunate produced by the Mongol response of the 1280s was one of the substantial causes of the shogunate’s eventual collapse in 1333.
The second invasion
Kublai Khan ordered the construction of a second, much larger invasion fleet through the late 1270s. He had completed the conquest of the Southern Song by 1279 and added substantial Chinese maritime expertise and shipbuilding capacity to the operation. The second invasion was an enormous undertaking by 13th-century standards: approximately 4,400 ships and 140,000 troops, divided into two fleets sailing from Korea and from the southern Chinese coast respectively, with the political intention of permanent occupation of Japan.
The Korean fleet sailed in May 1281; the Chinese fleet sailed in June. The two were to rendezvous at Hakata Bay in late June. The Korean fleet arrived on schedule and attempted landings at Tsushima and Iki; the Chinese fleet was delayed by storms and political squabbles in southern China. The combined operation was substantially uncoordinated.
The Mongol attack on Hakata in late June 1281 found the defensive wall in place and the samurai garrison fully mobilized. The systematic Mongol tactical advantages of the 1274 engagement no longer existed; the Japanese had reorganized their cavalry doctrine specifically against the Mongol approach. The bay fighting lasted nearly two months — the longest sustained combat in 13th-century East Asian naval-military history. The Mongols could not establish a beachhead.
In mid-August the combined Mongol-Chinese fleet had withdrawn to the bay of Imari, approximately fifty kilometres southwest of Hakata, to regroup. On 15 August 1281 a second typhoon struck. The records are substantially more detailed than for 1274 (the Yuan dynasty maintained military-administrative archives that survived its 1368 fall, and the Japanese samurai-clan records have been preserved at substantial private archives). The typhoon destroyed approximately 4,000 ships and killed approximately 100,000 troops. It was one of the largest single-event mass casualties of the medieval period and effectively ended Mongol military ambitions toward Japan. Kublai began planning a third invasion through the 1280s but never executed it; he died in 1294.
The name
The Japanese cultural interpretation of the two storms identified them as kamikaze — the divine wind, sent by the gods of the imperial Shinto religious tradition to protect Japan from foreign invasion. The interpretation was substantially shaped by the political-religious framework of the Kamakura court, which had spent the campaign performing ritual prayers at the major imperial shrines (most prominently the Ise Grand Shrine and the Hachiman shrine at Usa) and which interpreted the storms as the direct material response of the kami to those prayers. The conceptual association of the kamikaze with Japanese imperial-divine protection became one of the foundational images of Japanese political-religious tradition.
The term was revived, with substantial new political content, in late 1944. Vice-Admiral Takijirō Ōnishi of the Imperial Japanese Navy authorized the formation of the Special Attack Units — the kamikaze — composed of pilots who would deliberately crash explosive-laden aircraft into Allied warships. Approximately 3,800 kamikaze pilots died in the operation between October 1944 and the surrender of August 1945. They sank approximately 47 Allied vessels and damaged approximately 300 more.
The 20th-century kamikaze mission used the name of the 13th-century storms with deliberate political intent: the same divine wind that had saved Japan from foreign invasion in 1274 and 1281 would, the doctrine promised, do it again. It did not.
The wrecks
Substantial archaeological investigation of the 1281 invasion fleet has been conducted in Imari Bay since the 1980s. The bay has yielded approximately a thousand individual finds including substantial portions of Chinese-built ship hulls, iron and stone anchors, ceramics, weapons, and personal artifacts. The recovered material has confirmed substantial portions of the 13th-century textual accounts and has produced detailed reconstructions of the construction methods used in the rushed Mongol shipbuilding programs of the late 1270s. The construction quality of the 1281 ships was, in fact, significantly poorer than the 1274 fleet — a consequence of the four-year rushed production schedule against an already-conquered Korean shipbuilding population.
The typhoon of 15 August 1281 was the immediate cause of the Mongol catastrophe. The structural condition of the ships was the proximate cause. The Mongol political decision to mount an invasion using vessels built by impressed conquered populations under extreme time pressure was the deeper cause. The samurai garrison of Hakata Bay never had to defeat the second invasion. The weather and the shipwrights did it for them.