The Japan Steel Works, Ltd.

The Japan Steel Works was incorporated at Muroran in Hokkaido in November 1907 as a joint venture between Hokkaido Colliery and Steamship and the British armament firms Armstrong Whitworth and Vickers, set up because the government wanted naval guns forged at home and had neither the technique nor the capital to do it alone. That origin still shapes the company. JSW runs six business lines. Plastics Machinery Business builds twin screw compounding extruders, pelletizing systems and biaxially oriented film lines. Molding Machine Business covers all-electric injection machines from 300 kN to 1,800 kN clamping force, very large multicolour rotary machines and magnesium injection equipment. Industrial Machinery Business supplies semiconductor and electronics production plant including laminators and vacuum hot presses. Material and Engineering Products Business forges components for power generation, refining and gas. New Business covers photonics, composite and metallic materials. Ordnance Business is the sixth.

That sixth line matters out of proportion to its size. The Hiroshima Works is the only plant in Japan able to manufacture artillery, and it produces the 120 mm smoothbore gun for the Type 10 main battle tank, the 105 mm rifled gun for the Type 16 manoeuvre combat vehicle, the 62-calibre five-inch mount fitted to Maritime Self-Defense Force destroyers, and missile launch tubes and launchers. JSW also produces the Type 19 155 mm wheeled self-propelled howitzer, building the Rheinmetall MAN HX44M chassis under licence in Japan after prototypes went to the company for testing in 2018 and the vehicle was accepted into Ground Self-Defense Force service in 2020. In August 2023 the company signed a licence agreement with Patria to manufacture the AMV 8x8 in Japan for the wheeled armoured personnel carrier programme replacing the Type 96. A new assembly building at Hiroshima was completed to expand gun and launcher output against Japan's defence buildup plan. Older work at the same plants included the gun and turret for the Type 75 155 mm self-propelled howitzer, which served the ground force from 1975 until 2014.

Outside ordnance the company's distinctive asset is heavy forging. JSW is the only maker able to produce nuclear reactor pressure vessel shells as single pieces without welds, a bottleneck that historically had utilities booking slots years ahead, and the same presses turn out crankshafts, turbine rotors, wind turbine main shafts and clad steel plate. Muroran narrowed to gun barrels and large naval forgings a century ago, and the 10,000 tonne press installed there made it the largest private arms plant in the country, turning out the barrel work for the battleship Yamato. Headquarters sit at Gate City Ohsaki in Tokyo, the shares trade in Tokyo under code 5631 and the company is a Nikkei 225 constituent within the Mitsui group orbit. For a buyer the useful summary is that JSW is a metallurgy and heavy machinery firm whose defence work is narrow, sovereign and hard to replace, rather than a systems house. It supplies guns, barrels, launchers and vehicles, and leaves fire control, sensors and command systems to others.