関門海峡
The was the first undersea tunnel in Japan. It goes underneath the Kanmon Straits, connecting the islands of Honshu and Kyushu. It is an important link in the Japanese rail network. Its construction began in 1936, and it was completed in November 1942, during the Pacific War. The Honshu-bound tunnel is long, the Kyushu-bound tunnel is . Track gauge is , and its electric power supply is at 1,500 volts DC.