Hikari Naval Arsenal

Hikari Naval Arsenal (光海軍工廠) was the seventh naval arsenal of the Imperial Japanese Navy, established on October 1, 1940 on approximately 4 square kilometers of coastal land in Hikari City, Yamaguchi Prefecture. The site was chosen for its sheltered coastline along the Seto Inland Sea and proximity to the major naval base at Kure.

The arsenal initially opened with a gun production section staffed by 40 officers and 451 employees. Rapid wartime expansion followed: a steel section and torpedo section were added in 1941 (bringing personnel to 230 officers and 9,000 workers), a machinery section in 1942, and a bomb production section in 1943. By war's end the facility had grown into one of Japan's largest military-industrial complexes, employing approximately 30,000 people including about 6,500 mobilized student workers (学徒動員).

The arsenal became critically important for Japan's special attack weapons program. A kaiten (回天) base was built within the arsenal grounds in 1944 (the Hikari kaiten unit was formed on November 25, 1944), making it a training and sortie base for these human torpedoes — modified Type 93 torpedoes fitted with a cockpit allowing a pilot to guide the weapon to its target in a suicide attack. The Imperial Japanese Navy formed the Second Special Attack Force at Hikari on March 1, 1945, for conducting kaiten operations. At the start of 1945, approximately 70 kaiten were stationed at Hikari along with 50 technicians. After Japan's surrender, Allied forces discovered and destroyed 52 kaiten remaining at the base.

On August 14, 1945 — just one day before Emperor Hirohito's surrender broadcast — the arsenal suffered a devastating air raid by the United States XXI Bomber Command (Mission 325). A total of 167 B-29 Superfortress bombers attacked in five waves over approximately one hour. The bombing killed 738 people: 51 military personnel, 554 civilian employees, and 133 mobilized students. This was one of the last major aerial bombardments of World War II.

After the war, the arsenal site was converted to industrial use. Today the former grounds are occupied by Nippon Steel's Yamaguchi Steelworks Hikari facility and Takeda Pharmaceutical Industries' Hikari factory. A kaiten monument erected in 1996 and other memorials in the area honor the victims of the August 14 air raid and the kaiten pilots who trained and deployed from Hikari.