An Armada's fatal flaw
In 1281, Kublai Khan, grandson of Genghis Khan, assembled one of the largest naval invasion forces in history to conquer Japan. The second of two invasion attempts, this massive fleet consisted of two parts: an "Eastern Route Army" of 900 ships from Korea and a "Southern Army" from China with 3,500 ships. Together, they carried an estimated 140,000 soldiers and sailors. Yet, this formidable armada had a significant weakness in its very construction.
Archaeological analysis of ship timbers recovered from the seabed off Takashima Island reveals that many vessels in the Southern Army fleet were not true ocean-going warships. Instead, they were flat-bottomed river boats, likely requisitioned and hastily constructed after the Mongols' recent conquest of Southern China. This design, ideal for inland waterways, lacked the deep keel necessary for stability in open seas. This structural vulnerability proved catastrophic when the fleet encountered a powerful typhoon. On August 15, 1281, the storm struck the anchored fleet in Hakata Bay, wrecking the improperly designed ships and ending the invasion. The Japanese named this storm "kamikaze," or "divine wind," believing it was a sign of divine protection.
The seabed's secrets
For centuries, the story of the "divine wind" was primarily known from historical texts. In 1980, Professor Torao Mozai began the first modern underwater surveys off Takashima, using sonar to search for physical evidence. Since then, maritime archaeologists, including teams from the University of the Ryukyus, have made significant discoveries. They have located the remains of multiple ships from the doomed fleet, buried under sediment as deep as 15 meters below the surface.
Excavations have yielded more than 4,000 artifacts that show details of the invasion force. Recovered items include personal seals of Mongol commanders, iron helmets, bundled arrows, and ceramic grenades known as "tetsuhau". Divers have also found large wooden anchors, stone ballast, and sections of the ships themselves, including a 12-meter-long keel section. Analysis of the wood shows some timbers were felled as early as 1253, nearly three decades before the invasion. These discoveries confirm that the fleet was a mix of purpose-built warships and repurposed river craft, showing the structural flaw that led to its demise.