'Rabbit island' a dark outpost of Japan's chemical warfare

Researchers, peace activists work to preserve history of poison gas use, urge Tokyo to acknowledge role as aggressor

By HOU JUNJIE in Hiroshima and Yokohama | China Daily | Updated: 2026-09-18 07:07
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Akio Kusumoto, a member of a Japanese civic group engaged in passing on atomic bomb information, introduces the history of the island. CHEN ZEAN/XINHUA

Beyond Okunoshima

Okunoshima was only one part of Japan's wartime chemical warfare system.

During the war, Japan developed a network covering the production of chemical agents, personnel training and battlefield use. Okunoshima produced the chemical agents, while the Sone production facility in Kitakyushu, Fukuoka prefecture, placed them in munitions. The Imperial Japanese Army's Narashino School in Chiba prefecture trained personnel in chemical warfare.

Wartime production reports from the Sone facility have in recent years been uncovered at the National Archives of Japan by Seiya Matsuno, a Japanese historian and researcher at the International Peace Research Institute of Meiji Gakuin University. The documents detail the production of chemical munitions, as well as accidents and injuries during the process.

Matsuno's research shows that the Sone facility produced about 1.48 million poison gas munitions. Chemical filling there took place from 1938 to 1944.

By the time the chemical warfare system took shape, the use of poison gas in war had already been prohibited under international law. The 1925 Geneva Protocol prohibited the use in war of asphyxiating, poisonous or other gases.

Yet from 1929 until 1945, Japan continued producing large quantities of chemical agents for use in chemical weapons.

According to China's Ministry of Foreign Affairs, invading Japanese troops used chemical weapons on a large scale in China, causing more than 200,000 Chinese military and civilian casualties.

Japan's defeat did not bring an end to the harm caused by its chemical weapons.

Large quantities of chemical weapons were abandoned in China after Japan's defeat. According to China's Ministry of Foreign Affairs, about 400,000 such weapons have been discovered at more than 120 sites across 18 provincial-level regions in China. Since the end of the war against Japanese aggression, abandoned Japanese chemical weapons have caused more than 2,000 Chinese casualties.

Maiko Sugamoto, director of the Japan-China Cooperative Fund for Victims of Chemical Weapons, has long been involved in lawsuits on behalf of victims of chemical weapons abandoned by the Imperial Japanese Army in China.

She said these weapons can still resurface decades after the war during construction and excavation.

"Decades after the war ended, it is still ordinary people who suffer from the harm left behind," she said.

Speaking at an event on Okunoshima in early September, Fang Wei, vice-consul-general of the Chinese Consulate General in Osaka, said the Japanese government should face up to its historical responsibility and current obligations, take concrete and effective measures to accelerate the disposal of chemical weapons, and "restore safe and clean land to the Chinese people at an early date".

Under the Chemical Weapons Convention, which entered into force in 1997, Japan is responsible for destroying the chemical weapons it abandoned in China. In 1999, the Chinese and Japanese governments signed a memorandum setting out arrangements for their destruction.

The destruction process was originally due to be completed by 2007, but the plan has since missed its deadline four times amid insufficient attention and input from the Japanese side.

Remembering history

In late August, a series of events in Yokohama revisited the Imperial Japanese Army's chemical warfare through exhibitions of photographs and historical materials, as well as talks by Japanese researchers, photojournalists and others who have studied its history.

Among the works on display were photographs documenting Okunoshima's poison gas history by Japanese photojournalist Kenji Higuchi, who has covered the island's wartime history since 1970.

"They did something terrible, and it was a disgrace to the country, so they wanted to erase it from history," Higuchi said. "This history must be told clearly. What was wrong was wrong, and what was right was right. We need to be able to distinguish between the two."

Masao Sawazono, a visitor from Yokosuka, knew little about Japan's wartime poison gas and chemical warfare before listening to Higuchi speak at the event.

Nobuharu Goi, one of the organizers and a representative of the 731 Network, a Japanese civic group studying Japan's wartime biological warfare, noted that many of the materials on display had been collected and preserved by Japanese civic groups since the 1990s. Nearly 200 people attended the events on the opening day.

Having helped organize more than 10 such events over the years, Goi sees the exhibitions and lectures as a way to preserve the historical record and keep this history in the public consciousness.

Yet, passing this history on to a new generation is becoming increasingly difficult.

Sugamoto, who gave a talk as part of the Yokohama event series, said younger generations have begun taking over the task of telling stories of Japan's wartime suffering, including those of atomic bomb survivors.

"But when it comes to the history of the harm Japan inflicted during the war, we have yet to see a younger generation take over and continue telling these stories," she said.

With longtime volunteer guides on Okunoshima growing older, Sugamoto hopes more young Japanese will learn about the country's wartime aggression.

"Our generation and those younger than us must continue telling these stories and pass this history on," she said.

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