Toyota Motor Koromo Plant (now Honsha Plant)

The Toyota Koromo Plant, formally established as the main production facility of Toyota Motor Co., Ltd., was completed on November 3, 1938, in the town of Koromo, Aichi Prefecture. The site covered approximately 500,000 square meters with a building area of roughly 200,000 square meters, making it one of the largest integrated automobile manufacturing facilities in Asia at the time. The plant was designed for start-to-finish mass production, encompassing casting, forging, machining, stamping, body assembly, painting, and final assembly — all under one roof. Its construction cost 45 million yen, a massive investment that reflected the ambition of founder Kiichiro Toyoda to build a world-class automobile industry in Japan.

The origins of the plant trace back to the Automobile Department established within Toyoda Automatic Loom Works (豊田自動織機製作所) in 1933. Kiichiro Toyoda, son of the legendary inventor Sakichi Toyoda, leveraged profits from the loom business to fund automotive research. The first Toyota Model G1 truck rolled off the line in 1935, and the Model AA passenger car followed in 1936. When Toyota Motor Co., Ltd. was spun off as an independent company in 1937, the Koromo Plant became its heart.

In January 1944 Toyota Motor was designated a munitions company (軍需会社) under the Munitions Company Act, placing the Koromo Plant under the control of the Munitions Ministry. Production shifted overwhelmingly to military trucks — the 4-ton KB model and, from November 1943, the wartime-standard KC model, designed to save about 30 percent of the steel because of severe material shortages. The plant also manufactured components for aircraft engines, including the Ha-13 radial engine, with raw blanks produced in the forging plant and light alloy foundry. Toyota jointly established Tokai Aircraft Industries with Kawasaki Heavy Industries at the request of the Army Air Headquarters, and separately developed a two-seater helicopter prototype in 1943. By the war's end, approximately 9,500 workers were employed at the plant.

On August 14, 1945 — just one day before Japan's surrender — the Koromo Plant was struck by an air raid conducted by the U.S. Army Air Forces. Approximately a quarter of the plant's facilities were destroyed. The following day, while workers were attempting to repair the damage, Emperor Hirohito's broadcast announcing Japan's surrender was heard. Despite the devastation, production resumed remarkably on August 17. Toyota submitted applications to the Allied occupation forces on October 10, 1945 for permission to convert the Koromo Plant and other facilities to civilian production, which was granted on December 8, 1945. Many workers left in the chaotic postwar period, reducing the workforce from about 9,500 to roughly 3,700.

Today the Koromo Plant is known as the Honsha Plant (本社工場) and remains Toyota Motor Corporation's headquarters facility. Toyota's earlier prototype plant, where the first prototype cars were built in 1935, stood not at Koromo but in Kariya (on the grounds of what is now Aichi Steel's Kariya plant); part of that building was relocated in 2005 to the Toyota Commemorative Museum of Industry and Technology in Nagoya. The town of Koromo was renamed Toyota City (豊田市) in 1959 in honor of the company that transformed it from a rural silk-producing town into one of Japan's premier industrial cities.