Kyushu Aircraft Zasshonokuma Plant

The Kyushu Aircraft Zasshonokuma Plant (九州飛行機雑餉隈工場) was the headquarters factory of the Kyushu Aircraft Company, located at Zasshonokuma, then on the outskirts of Fukuoka City; the site stretched from what is now Minami-Fukuoka Station to the present JGSDF Camp Fukuoka in Kasuga City, Fukuoka Prefecture. It is historically significant as the birthplace of the J7W1 Shinden — one of the most radical fighter aircraft designs of World War II.

Company Origins: Watanabe Iron Works to Kyushu Aircraft

The company traces its roots to Watanabe Iron Works (渡邊鉄工所), which began in 1886 as a machine works in Hakata and was incorporated as a separate company in 1916. In 1930 the company moved its works to Zasshonokuma, and from 1935 it built aircraft there, on a vast 120,000-tsubo (approximately 396,000 square meters) site near what is now JR Minami-Fukuoka Station. The factory steadily grew through Imperial Japanese Navy contracts, producing floatplane reconnaissance aircraft and trainers.

In 1943, with wartime production demands intensifying, the aircraft division was split off as Kyushu Aircraft Company (九州飛行機株式会社), while Watanabe Iron Works itself was renamed Kyushu Heiki (九州兵器). By this time the Zasshonokuma Plant had become a major naval aviation production center, manufacturing 16 types of aircraft including approximately 1,200 Zero reconnaissance floatplanes (E13A Jake) and other naval aircraft. Additional factories operated at Kashii and Wajiro along the Fukuoka coast.

The Shinden (震電) — Japan's Canard Interceptor

As B-29 Superfortress raids devastated Japanese cities from late 1944, the Imperial Japanese Navy urgently sought a high-performance interceptor capable of rapidly climbing to intercept the bombers at high altitude. Technical Lieutenant Masayoshi Tsuruno (鶴野正敬) of the Navy Air Technical Arsenal (空技廠) proposed a revolutionary canard-configuration design — with small forward wings (canards) mounted ahead of the cockpit, main wings swept back at the rear, and a six-bladed pusher propeller driven by a 2,130-horsepower Mitsubishi MK9D (Ha-43) radial engine mounted behind the pilot.

This layout offered several theoretical advantages: the forward canard eliminated the need for a conventional tail, reducing drag; the pusher configuration allowed a nose-mounted battery of four 30mm Type 5 cannon without propeller synchronization problems; and the design promised a maximum speed of 750 km/h (466 mph) — faster than any operational Allied fighter at the time.

The Navy designated it the Experimental 18-Shi Interceptor Fighter (十八試局地戦闘機). On June 4, 1944, construction of the first two J7W1 prototypes began at the Zasshonokuma Plant. Tsuruno personally oversaw the design and construction process at the factory.

Prototype Completion and Test Flights

The first prototype (試作1号機) was completed on June 10, 1945. It was disassembled and transported by road to Mushiroda Airfield (席田飛行場, now Fukuoka Airport) on June 15 for reassembly and ground testing.

After Tsuruno bent the propeller tips during a taxiing trial in July, the Shinden made its maiden flight on August 3, 1945, flown by Kyushu Aircraft test pilot Miyaishi. The aircraft flew successfully but exhibited a tendency to pull to the left due to propeller torque — a known issue with pusher-propeller designs that would have required a slight offset of the vertical stabilizer to correct. Two additional test flights were conducted on August 6 and August 8, 1945. Total flight time across three flights was approximately 45 minutes.

The Navy had already ordered mass production: 30 units per month from Kyushu's Zasshonokuma Plant and 120 per month from Nakajima's Handa Plant. However, Japan's surrender on August 15, 1945, ended all plans. The second prototype was never completed.

Fate of the Aircraft

After the surrender, the sole completed Shinden at Mushiroda Airfield was seized by a U.S. Navy Technical Air Intelligence Unit in late 1945. The aircraft was dismantled, crated, and shipped to the United States for evaluation. It was reassembled but never flown by American test pilots. The U.S. Navy transferred the aircraft to the Smithsonian Institution in 1960. Today, the forward fuselage section is on display at the Steven F. Udvar-Hazy Center of the National Air and Space Museum near Washington, D.C. — the only surviving Shinden airframe in the world.

A full-scale replica of the Shinden, originally built for the 2023 film 'Godzilla Minus One' (ゴジラ-1.0), is now permanently exhibited at the Tachiarai Peace Memorial Museum (大刀洗平和記念館) in Chikuzen, Fukuoka Prefecture — fittingly located in the same prefecture where the original was built.

Postwar Fate of the Factory

After Japan's surrender, the Zasshonokuma Plant was seized by U.S. occupation forces in December 1945 and housed a 1,500-man American detachment. The factory was designated a reparations facility under GHQ orders. With the outbreak of the Korean War in 1950, the reparations designation was lifted. The successor company, Watanabe Automobile Industry (渡辺自動車工業), relocated to nearby Kasuga in 1953.

The former factory grounds were transferred to the newly established National Police Reserve (later the Japan Ground Self-Defense Force), becoming JGSDF Camp Fukuoka (陸上自衛隊福岡駐屯地). Remarkably, several original wartime factory buildings survive within the base, continuing to serve as supply warehouses for the JGSDF quartermaster corps — among the few intact remnants of Japan's wartime aircraft industry still in daily military use.