Okunoshima is not unique among the some 3,000 islands dotting Japan's Seto Inland Sea, between Hiroshima prefecture and the island of Shikoku. Neither the biggest nor the smallest, the tiny land mass measures less than a square kilometre. There's no natural water supply — that's shipped in from the mainland — and as of 2010, only 26 people live on the island, but Okunoshima is far better known for its population of four-legged residents.
There is a strange propensity in Japan to name islands after cute critters, and myths abound of how beloved animals arrived in several remote destinations spanning the Japanese archipelago. Tashirojima, for example, acquired its famous cats during the late Edo period (1603-1868), to act as pest control on the island's silkworm farms, a wholesome, practical explanation.
The origin story for Okunoshima's rabbit population, however, leading to the island's colloquial renaming as Usaginoshima, is anything but what one might expect in regard to a tourist island overrun with cute little bunnies, and the more the layers of history are gnawed back, the more sinister and un-cute this place becomes.
Though motives remain unclear, local authorities sought to make Okunoshima a tourist destination in 1958. The island was (and still is) part of the Setonaikai National Park, designated in 1934, but during those interim decades, some dark secrets were buried, burned or otherwise disposed of. For a while the island was not included on maps but, in the end, no matter how light and fluffy, no matter how "kawaii", nothing could obscure the island's production of a massive, secret stockpile of chemical weapons.
Japan was one of 38 signatories to the 1925 Geneva Protocol, prohibiting the use of chemical or biological weapons. However, many countries continued to produce and stockpile them, including Japan, beginning in 1929.
"The chemical weapons factory had to be close to the mainland in order to recruit the workers," says historian Yuki Tanaka, former professor of history at Hiroshima University. "They couldn't set up the factory far away from the main island, so they chose Okunoshima."
Now based in Melbourne, Australia, and an outspoken critic of Japanese politics and military history, Tanaka says the extra convenience of Okunoshima was the presence of Geiyo Fortress, a collection of pre-existing military structures still visible to this day, built in the late 19th century and manned during the Russo-Japanese war (1904-05).
Once Okunoshima was established as Japan's centre of chemical weapons production, the military government proceeded to erase it from maps as a national secret. And not for the first time: due to the presence of the fortress, it had been removed from earlier Meiji (1868-1912) and Taisho era (1912-26) maps. But with residents of neighbouring Takehara employed as workers, "Okunoshima wasn't really secret," says Tanaka. "The local people knew what was going on."
It was the rest of Japan that would remain ignorant of what would later be dubbed Dokugasu no Shima (Poison Gas Island). Yamauchi Masayuki is executive director of the Poisonous Gas Island History Research Institute, the citizen group behind the island's Poison Gas Museum. The aim of the museum is to pass down the history of damage and harm caused by chemical weapons from Okunoshima and "create a world that does not use chemical weapons", he writes via email.
The official name may sound like a tasteless euphemism, but "the Imperial Japanese Army Institute of Science and Technology" produced "all sorts of things" on the secret island, according to Tanaka. "Phosgene, mustard gas, hydrocyanic acid, chlorine, lewisite, sneeze and nausea gas, adamsite, you name it. The most dangerous one, of course, is mustard gas," he says.
Nothing is mentioned in the Geneva Protocol regarding the production of chemical weapons, so no matter how much mustard gas Japan produced and stockpiled, it contravened no international agreements. Tanaka says the facility was responsible for producing more than six kilotons of mustard gas and tear gas, and what did break the Geneva Protocol was that many of these chemical weapons went on to be tested and deployed by Japan as an occupying force in the time leading up to and during the World War II, predominantly in China.
After the Japanese invaded, in 1931, "chemical weapons were produced in Okunoshima then transported to Unit 731 in Harbin", part of Japan-controlled Manchuria, known as Manchukuo, says Tanaka. Unit 731 — headed by Surgeon General Shiro Ishii, a microbiologist — was part of the Epidemic Prevention and Water Purification Department of the Kwantung Army and contrary to the utilitarian designation, "they tested on Chinese POWs, but [they were] not actually POWs, they were mainly the people involved in the anti-Japanese movement, anti-Japanese activists. About 3,000 people were killed".
Tanaka confirms that, armed with a huge budget rubber-stamped by the highest authority, "all sorts of nasty, nasty experiments" were not just confined to labs. One operation included airdropping plague-carrying fleas on Changde, Hunan province. "[Emperor] Hirohito also knew about Unit 731's research, because it was a huge, huge budget."
It is not known, however, if the finer details of the research were divulged.
These illegal instruments of war were not only used in Harbin, but taken wherever the Japanese went in China, including Nanjing and Shanghai. And as the war ended, these weapons were dumped. Years later, civilians scooped up these curious objects — not knowing what they were — in an effort to dispose of them. "Obviously they were injured and many of them died," Tanaka says. "So the Chinese actually sued the Japanese government, or requested compensation. The Japanese government paid to some extent."
But it was not until 2010 that the official destruction of some of these abandoned chemical weapons began. A mobile destruction facility was inaugurated in September of that year in Nanjing and, having completed its second phase in Shijiazhuang, Hebei province, in 2014, the facility arrived in Wuhan, Hubei province; northeast China and the area around Harbin began to be tackled only as recently as 2019. The largest burial site ever discovered was in Harbaling, Jilin province, where more than 330,000 abandoned chemical weapons were unearthed.
One of the great injustices has been the lack of recognition for the crimes of Ishii and Unit 731. By comparison, those involved in Nazi human experimentation were tried, and many found guilty of war crimes at the Doctors' Trial in Nuremberg, in 1947.
"The United States was involved to cover up this Unit 731," says Tanaka. "[The US] already had chemical weapons, but bacteriological weapons, this was a new area. Research on bacteriological weapons was far, far behind in the US during the war."
And so a deal was struck. In exchange for information on bacteriological weapons, those involved in the actions of Unit 731 would be granted immunity; there was a fear that the Soviets would gain access to this valuable trove of knowledge.
The Poison Gas Museum's Yamauchi also claims it was this "opposition from the United States" to allowing the use of chemical weapons to come to light during the 1946 Tokyo War Crimes Tribunal that kept not only Japan but the whole world in the dark regarding Okunoshima. At the tribunal, a single token reference to experiments with "poisonous serums" was made, inexplicably, by one David Sutton, assistant to the Chinese prosecutor.
Up to that point, the secrecy surrounding Japan's wartime use of chemical weapons is echoed in transcripts of the hearing: "This is something entirely new, we haven't heard before. Are you going to leave it at that?" asked the startled president of the tribunal, William Webb, almost urging him to say more. Sutton replied: "We do not at this time anticipate introducing additional evidence on that subject."
Too vague to be pursued, the claim was dismissed. The whole endeavour remained a secret, enabling many former Unit 731 members to evade punishment. Alternatively, the Soviet Union had some success, with several researchers they had previously arrested and who were tried at the Khabarovsk War Crime Trials in 1949.
"Many of them [were] actually top medical researchers, and many of them went back to their university's old positions, [or] became a professor in medical schools, hiding their background," says Tanaka. Several former Unit 731 members, including Masaji Kitano, Hideo Futaki and Ryoichi Naito, for example, went on to found Japan Blood Bank (afterwards Green Cross) in 1950, eventually becoming - via several mergers - Mitsubishi Tanabe Pharma Corporation.
"Yes," says Tanaka, "the head of Unit 731, General Ishii, was invited to a military research facility in the United States, in Utah. He gave a series of talks to the scientists of the US forces." Just a few years before his alleged visit, the Dugway Proving Ground, in Utah, was home to the so-called Japanese Village, where the US Air Force honed their later firebombing of various Japanese cities.
Richard Drayton, professor of history at King's College London, instead locates Ishii's visit as having been to Fort Detrick, Maryland: Dugway's parent facility and the centre for the US biological weapons programme. And there are additional claims, including by Tanaka, that Ishii was given "a huge amount of money" in exchange for information.
The mystery of Okunoshima for decades following the war suddenly becomes clear: to cover up the presence of bacteriological weapons, knowledge of which was coveted by the US, the chemical weapons also had to be covered up.
"During the war, around 200 rabbits were kept in cages for experiments to test the effects of poisonous gas," says Yamauchi. One theory for Okunoshima's population of bunnies has them leaping to freedom at the end of the war, but that can safely be debunked: "The rabbits kept for poisonous gas experiments were disposed of at the time of Japan's defeat, and have nothing to do with the current rabbits," he says.
After the poison-gas period, the island was requisitioned by the US during the Korean war (1950-53), specifically as an ammunition depot.
A former military building on the island has been remodelled as a kokumin kyūkamura (literally "national holiday village"), an affordable hotel run by the local government; the beach has been beautified, and attractions added. Under the hotel's first manager, Hirofumi Nishiyoshi, an onsen (traditional hot spring) was dug in 1964.
"Although the poisonous gas factory had been treated, many factory traces still remained, and four guards were monitoring each of them 24 hours a day over two shifts," Nishiyoshi wrote in a pamphlet about the history of the hotel.
"Even now," says Yamauchi, "there are still tear gas canisters and the like in the air raid shelter."
And so Okunoshima has become a most unlikely resort island. Feeling relatively remote yet easy enough to reach from cities such as Hiroshima, the first tentative tourists started to arrive after the hotel opened in 1963.
While the location and amenities may have been promotion enough, a popular story goes that junior school children released eight rabbits onto Okunoshima during a 1971 field trip, Nishiyoshi having had the bright idea to introduce a mascot-type creature to the island in 1965. There were also plans to keep deer - perhaps modelled after Itsukushima's or Nara's tourist-luring deer population - even monkeys, according to Hatsuichi Murakami, a former curator of the Poison Gas Museum. But rabbits won the day.
"I got five baby rabbits and started keeping them," Nishiyoshi is quoted as saying in the booklet about the hotel. "For food I was giving them vegetable scraps from the kitchen. I felt that their numbers increased or decreased depending on the amount of food available."
"Rabbits need to eat not just every day but throughout the day. That to me is the biggest problem with the island," says Margo DeMello, assistant professor of anthrozoology at Carroll College, in Montana, the US, who conducted a research project with Okunoshima's feral rabbit population in 2016. "My assessment is that mortality is very high, and that most of the mortality is associated with the inconsistent food which wreaks havoc on a rabbit's digestive system."
Indeed, in 2019, The Japan Times published three letters from readers that raised concerns for the welfare of Okunoshima's rabbits. "Almost all the rabbits were injured, sick or dying," read one; "Because they are domesticated and not wild, people need to help them," read another. While the official "Rabbit Island" website boasts of its being "home to over 1,000 rabbits", neither DeMello nor Yamauchi seems convinced this population is sustainable.
"Living naturally, the number of rabbits that can reside on Okunoshima, a small island with a circumference of only 4km, is about 300," Yamauchi says. "Currently there are more than 900. This is bad for [the] rabbits and bad for the nature of the island."
DeMello also cites rabbits fighting over food, resulting in wounds that often turn septic. "There is a lot of death on that island," she says, "but tourists don't see it because hotel staff pick up the bodies."
Many Google reviews echo this distressing reality, mentioning diseased rabbits, lack of natural food and injuries that go untreated, but the island still received TripAdvisor's Travellers' Choice award for 2020.
Regardless of the rabbits' welfare, Yamauchi admits their presence can help preserve the dark history of the island for future generations.
"Many relics of war remain, making Okunoshima the most suitable island for learning about peace," Yamauchi writes. "From now and forever I hope the island is a place not only for people to see rabbits, but also to learn how foolish and miserable war can be."
This story was first published in South China Morning Post.