Like the Suez, Panama, Magellan, and Gibraltar, the Kanmon Strait is a vital waterway that has shaped the fate of a nation. For many centuries, this channel separating the islands of Honshu and Kyushu has been a key maritime seaway linking the Sea of Japan to the Seto Inland Sea. Countless generations of pilots and captains have braved its treacherous reefs and fierce currents of up to 11 knots (20.3 km/h). The strait is approximately 15 nautical miles in length and 12 meters deep, and at its narrowest point has only half a kilometer of navigable width. The challenges of navigating its waters are intensified by its S-shaped bend, poor visibility, and narrow channel.

Geographically, the strait is relatively small in scale, but in geopolitical, historical, and cultural terms, it is a giant. Over the centuries, the waterway has been visited by saints, spies, and scholars. It has been witness to naval warfare and political upheaval, as well as the tragic death of an emperor. Over the centuries, it has gone by several names, including “Anato,” “Bakan,” and “Shimonoseki.”

Origins

Modern geologists estimate the Kanmon Strait was formed when the islands of Honshu and Kyushu separated roughly 6,000 years ago. However, Japanese myth states the Kanmon Strait was formed early in the third century, as Empress Jingū was traveling south to suppress uprisings by the Kumaso, a group of indigenous peoples who lived in what is now Kyushu.
During her journey, Empress Jingū stopped at a cave called Anato. The cave miraculously split in two, and the great rent in the earth became the strait.

A Heian Tragedy

Toward the end of the twelfth century, Japan was plunged into conflict as the Taira and Minamoto clans became embroiled in the Genpei War (1180–1185). The conflict ended with the Battle of Dan no Ura, on the shore of the Kanmon Strait. The Taira warriors, realizing their inevitable defeat, threw themselves into the deadly currents rather than face the disgrace of capture. During the battle, the child emperor Antoku (1178–1185) plunged to a watery grave in the arms of his grandmother, Nii no Ama (1126–1185).

The Kanmon Strait from Muromachi to Edo

During the Muromachi period (1336–1573), envoy ships heading for Míng China (1368–1644) often passed through the Kanmon Strait to land at Moji. At the time, Moji served as a licensed trading port overseen by the powerful Ōuchi warlords, who controlled a vast portion of northern Kyushu. In 1550, Jesuit missionary Francis Xavier (1506–1552) landed at Shimonoseki while en route to Kyoto to proselytize at the imperial court. After being swiftly rejected by the Buddhists at the capital, he and his supporters returned to what is now Yamaguchi Prefecture to continue spreading Christianity.

In 1592, the shogun and de facto ruler of Japan Toyotomi Hideyoshi (1537–1598) sailed into the strait on his way to Osaka. His ship entered the waterway at low tide, when the reefs were most dangerous, but Hideyoshi was in a hurry. He pressed onward, and his ship’s hull ran aground, tossing him into the waves. He barely survived the ordeal.

In the early seventeenth century, renowned swordsman and philosopher Miyamoto Musashi (d. 1645) slew his opponent Sasaki Kojirō (dates unknown) in a duel on Ganryūjima Island. The story of their encounter is still retold today. During the subsequent centuries of the Edo period (1603–1867), Shimonoseki was a major port of call for westbound cargo vessels transporting kelp, herring, and other valuable commodities from Hokkaido and Tohoku to Osaka via the Kanmon Strait.

The Shimonoseki Campaign

Anti-foreign and anti-shogunal sentiment began to grow in western Japan after July 8, 1853, when US envoy Commodore Matthew Perry arrived in Uraga Bay with his flotilla of “Black Ships.” Tensions came to a head on June 25, 1863, when the Chōshū domain’s Maeda battery turned its 106-pound cannon on the SS Pembroke, a US merchant ship, as it passed through the strait. The incident made global headlines and prompted a series of naval skirmishes between Western nations and the Chōshū domain. These battles came to be called the “Shimonoseki Campaign” (1863–1864). In May of the following year, the British Admiral Augustus Kuper (1809–1885) led a fleet of British, American, Dutch, and French ships into the strait, where they overwhelmed the 2,000-strong Chōshū forces with their 110-pound Armstrong guns. The Chōshū rebels’ rallying cry of “revere the emperor, expel the barbarians!” (sonnō jōi) rang hollow, and Japan remained open to the outside world.

The Moji Port Boom Years and the Modern Strait

The Anglo-Japanese Treaty of Commerce and Navigation came into effect in 1899. It ended the unfair and restrictive trade policies that had begun with the Harris Treaty of 1858. After years of lopsided trade, Moji became a full-fledged international port, and the strait became a vital site for Japan’s burgeoning international trade in coal, rice, wheat, flour, and sulfur.

Moji’s fortunes blossomed again after Russia’s 1902 completion of the Chinese Eastern Railway, which linked Vladivostok to the ice-free deep-water port at Lǚshùn, in Dalian (known also as Port Arthur). In 1898, Moji’s port received more than 1,000 foreign ships, the fifth most of any port in the country. Many of those ships came to buy Chikuhō (Kyushu) coal, which had become a prized commodity in East Asia.

During World War II (1939–1945), US General Curtis LeMay (1906–1990) instigated the aerial mining of Japan’s inland waterways as part of Operation Starvation (1945). United States military intelligence identified the Kanmon Strait as “the single most vulnerable point in the enemy’s shipping position,” and it became a primary target for disruption. The naval minefields greatly hindered the import of oil, iron, and food, a loss that only worsened the country’s already strict wartime rationing.

Today, around 600 vessels traverse the straits each day, including both local vessels and ferries and container ships en route to major ports throughout Asia, North America, and Australasia. The currents remain as challenging as ever, and no vessel of 10,000 tons or more may pass through without a trained maritime pilot aboard.