Chosei Coal Mine Flooding Disaster
長生炭鉱水没事故
On February 3, 1942, the ceiling of an undersea coal mine tunnel collapsed off the coast of Ube, Yamaguchi Prefecture, flooding the mine and killing 183 workers — 136 Korean forced laborers and 47 Japanese miners.
History
The Chosei Coal Mine flooding disaster (長生炭鉱水没事故, also referred to as "Mizuhijo" / 水非常) occurred on February 3, 1942, when the ceiling of an undersea tunnel at the Chosei Coal Mine collapsed approximately 1.1 kilometers offshore from Ube City, Yamaguchi Prefecture. Seawater flooded the workings with devastating speed, killing all 183 miners trapped inside.
Of the 183 victims, 136 were Korean laborers conscripted under Japan's wartime forced labor mobilization policies, and 47 were Japanese. The disproportionate number of Korean casualties reflected the practice of assigning the most dangerous underground positions to colonial subjects while Japanese workers increasingly avoided the mine due to known safety hazards.
The root cause was illegal mining too close to the seabed. Regulations mandated a minimum depth of 47 meters below the sea floor, but the mine was operating at only 37 meters depth — a violation driven by wartime pressure to maximize coal production following Japan's entry into the Pacific War in December 1941.
Wartime censorship ensured that the disaster received minimal coverage, and it was largely forgotten until civic groups began investigating in the 1990s. The victims' remains still lie in the flooded mine beneath the sea. In August 2025, divers recovered the first bone fragments, intensifying calls for the Japanese government to recover and repatriate the remains.