ZAMA, Kanagawa Prefecture--A large metal panel that had been left at a home here for decades was recently identified as a component of a rare Imperial Japanese Navy interceptor fighter.

It was apparently taken by a worker at a factory where the planes were manufactured.

An expert calls the find "astonishing" since the part from the Raiden wartime fighter is the only remnant of the plane known to exist in Japan. 

The body panel was kept as a storage cover following the war in the yard at the home of Takao Oya, 66, whose father and ancestors were involved in farming, near the naval factory, as his uncle reportedly worked at the plant.

The aircraft component has officially been confirmed through the city’s research and inspection as being from a Raiden. Oya donated it to the municipality on Jan. 17 for display at exhibitions and lecture sessions.

“I decided to donate the part because it apparently has historic value for the city,” said Oya. “I would like as many people as possible to see it and get an opportunity to think of peace.”

An expert described the fragment as an important industrial relic that could provide clues to Japan’s advanced technologies at the time. As Raiden were produced at the Koza naval arsenal, which was located in Zama, the city called the find “an extant witness to local history.”

Raiden were developed by the Imperial Japanese Navy toward the end World War II to intercept U.S. B-29 bombers and other planes in defense of Tokyo.

Although the model had a shorter range than the renowned Zero fighter, its climbing, acceleration and attacking abilities were excellent.

For those reasons, Raiden were adopted as the mainstay fighter of the Atsugi base in Kanagawa Prefecture and other vital facilities.

After mass production on the interceptors started in 1943, a total of only 500 units, including 100 manufactured at the Koza arsenal, were made.

As the aircraft were seized by the U.S. military following the end of the war, one preserved at an aviation museum in California is the only known Raiden still in existence. No bodies or parts of the model had been found and confirmed in Japan.

Measuring 150 centimeters by 100 cm, the recently discovered body piece is an external panel on the front of the cockpit, made of layers of duralumin and aluminum. Even though about 75 years have passed since its production, no significant damage can be found on it.

The size of the curved fragment suggests how wide the aircraft’s front body was to mount the most powerful engine of the time.

According to aviation historian Bunzo Komine, who examined the part, the cutting-edge, world-class technologies were adopted for the Raiden, which was the first Japan-made huge machine mass-produced through the electric welding method and also with stronger Phillips screws.

As the discovered external panel was riveted more finely than that of mass-produced ones and does not have sections to be connected with other parts of the body, it is considered to be a “model part.”

Young male workers at the Koza arsenal are said to have created Raiden based on model parts developed by the Nagoya aircraft plant of Mitsubishi Heavy Industries Ltd.

“As it is a model, the component was finished elegantly with the most exceptional techniques,” said Komine. “It is a historic industrial relic because it shows the mechanical technologies of the time.”

Hiromi Tanaka, professor emeritus of Japanese modern military history at the National Defense Academy, called the discovery of a Raiden component "astonishing."

He noted that fighter aircraft were typically demolished due to dire shortages of building supplies after the war, so original components can rarely be found.

“I was surprised that such a large object has remained in existence after so much time has passed,” said Tanaka. “An increasing number of people do not know that Japan was involved in warfare. It is evidence of the war. I want people to imagine what the time was like.”

The arsenal, which started operations in 1943, included among its workers the famed writer Yukio Mishima (1925-1970). Of its 10,000 laborers, 8,400 were boys from Taiwan, which was under Japanese rule in those days. Amid increasingly intensified air raids, the plant was relocated to an underground site to continue making Raiden.

Osamu Furukawa, 61, a teacher at a Zama city-run junior high school, who has been researching the local history, studied the panel at Oya’s residence and explained the links between the part and Raiden through the internet and lecture sessions.

“The part is so light that it can be moved even with a single finger, and no signs of decay can be found,” Furukawa said. “I can see through it the feelings and thoughts of people who made the product and risked their lives flying the plane.”