was a naval arsenal located in Hikari, Yamaguchi Prefecture, Japan. It opened on October 1, 1940. It produced steel, engines, cannon, torpedoes, and bombs for the Imperial Japanese Navy. It was bombed on the afternoon of August 14, 1945 (the day before the official Surrender of Japan) by four B-29 bomber groups. The raid was reported to have taken place after Emperor Hirohito had begun his surrender message to the Japanese people. It was carried out by the XXI Bomber Command, classified as mission 325. Its target code was "Thunderhead"