Osaka Army Arsenal

The Osaka Army Arsenal was the largest army ordnance manufacturing facility in Japan. It began as the Zōheishi (造兵司), set up by the Meiji government inside Osaka Castle on March 4, 1870, when the castle area was being developed as the Army's centre; using machinery moved from the former shogunate's Nagasaki works and the guidance of foreign engineers, it began making guns and ammunition. It was renamed the Osaka Artillery Arsenal (大阪砲兵工廠) on October 10, 1879, the Osaka Factory of the Army Arsenal on April 1, 1923, and the Osaka Army Arsenal (大阪陸軍造兵廠) on April 1, 1940, though the old name remained in common use.

Its speciality was the casting and machining of heavy guns. It produced artillery pieces, small arms ammunition, armored vehicles, and a wide range of military equipment — field, fortress and anti-aircraft guns, shells and fuses, later tanks and vehicles — and has been called the largest military factory in Asia. It was also a source of modern metalworking technology: it cast water pipes and bridge steel for civilian use, and workers who left it helped create the metal industries around Osaka. The works spread east and north of the castle, with branch factories at Hirakata, Harima and elsewhere. At its wartime peak it employed over 60,000 workers — about 64,000 in August 1945, including mobilised students, the Women's Volunteer Corps and conscripted labour.

Osaka was heavily bombed from March 1945, but the arsenal itself was not the object of a concentrated attack until the last day of the war. The facility was a major target of Allied bombing and was largely destroyed by 1945: on August 14 about 150 B-29s dropped large numbers of one-ton bombs on it, destroying more than 80 percent of the works; Japanese sources record 382 deaths within the grounds. Bombs also hit the nearby Kyōbashi railway station, where sheltering passengers were killed — more than 200 identified dead, with the true number said to be higher. Japan announced its surrender the next day.

The vast site lay derelict for some twenty years because of unexploded bombs, and in the 1950s scrap thieves known as the "Apache" worked the ruins, later the subject of novels and films. The land was gradually redeveloped as Osaka Castle Park, Osaka Business Park and railway yards; Osaka-jō Hall stands on former arsenal ground. Few structures survive: the 1919 chemical analysis laboratory, the former main gate and guardhouse and a stone water gate. The laboratory, one of the only remaining factory buildings, is badly deteriorated and its preservation remains under discussion.