Kanmon Railway Tunnel, Railway tunnel beneath Kanmon Strait, Japan
The Kanmon Railway Tunnel is a 3614-meter rail passage running beneath the seabed of the Kanmon Strait, linking Shimonoseki on Honshu to Moji-ku on Kyushu. It carries trains of the San'yō Main Line through a single-bore tube with 1067-millimeter gauge track and overhead electric wires.
Construction began in 1936 to create Japan's first undersea railway connection and was completed in 1942 during wartime conditions. The tunnel replaced ferry services and enabled continuous rail traffic between the two main islands.
The tunnel represents Japanese engineering capabilities by connecting two distinct regional cultures through a permanent rail link that transformed inter-island transportation patterns.
The tunnel lies entirely below sea level and remains invisible to travelers, who experience it only from inside passing trains. Passengers often barely notice they are traveling underwater, as the crossing happens quickly and smoothly.
Engineers used four different tunneling methods during construction, including shield tunneling and immersed caisson techniques with compressed air. This combination was unusual for the time and helped overcome the changing geological conditions beneath the strait.
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