The Abandoned Poison Gas Plant of Okunoshima Island

The exterior of a former poison gas factory building

This tiny island boasts abundant, lush vegetation and sandy beaches and is surrounded by the beautiful, blue Seto Inland Sea. It is also home to many cute, furry bunnies, some of which will even climb onto people’s laps for food. However, despite its family friendly appeal, this is also a place with a horrifying past that brought sickness to the island’s workers and death to thousands in another country.

An island in the Seto Inland Sea

Okunoshima is part of Takehara in Hiroshima Prefecture and is one of many islands in the Seto Inland Sea. It lies about 2 miles (3 kilometers) from the mainland and is small, measuring only 2.5 miles (4 kilometers) in circumference. And it might have remained an obscure location had it not, in 1925, been designated as a secret Japanese poison gas-making facility.

Vegetation reclaims the factory walls.

Although Japan signed the 1925 Geneva Protocol – which prohibited the usage of chemical weaponry – this did not stop the government from building a chemical weapons plant on Okunoshima. The protocol didn’t actually ban the manufacturing and storage of chemical weapons, although the use of such toxic agents against humans was prohibited. This is probably why the factory was kept top secret at the time. The Japanese government even had the island removed from certain maps.


Some of the island’s newer residents

Okunoshima was a seemingly ideal site for the secret factory. Its distance from urban centers hid its purpose well, while its isolation also meant that if there were an accident at the site, it wouldn’t be a major disaster. However, the island was also not too far from other military facilities in Hiroshima Prefecture.


Looking out to sea from the island

For 16 years, between 1929 and 1945, the plant produced five varieties of poisonous gases, including sulfur mustard (or “mustard gas”), diphenylchloroarsine (or “sneezing gas”) and phosgene. The effects of these chemicals are horrific. Mustard gas is normally a slow and painful killer, with most deaths arising from secondary broncho-pneumonia and occurring after days or several weeks. As its alternate name suggests, diphenylchloroarsine induces uncontrollable sneezing, and high levels of it may also cause convulsions, vomiting and death. Like mustard gas, phosgene takes a while to act, but when it does, it is devastating to the human respiratory system. No wonder the use of agents such as these was banned.

The remains of the power generator building

Over 6,000 tons of deadly gases were made at Okunoshima. Emperor Hirohito personally directed that they be used in the war against China during the 1930s and 1940s, with the chemical weapons unleashed by the Japanese reportedly bringing about in excess of 80,000 casualties and the deaths of over 6,000 civilians and Chinese soldiers. In 1942 American president Franklin D. Roosevelt issued a stern warning to Japan to discontinue using chemical weapons in China – but this only led to Japan being more discreet in its use of poison gas.


A large factory building interior

Workers in the Okunoshima plant lived locally. Alternative employment opportunities may have been in short supply, given that the island’s fish preservation processor had to make way for the toxic weapons factory – but then again, jobs at the reactor did offer decent wages. According to researchers, around 6,500 people worked at the site during its operational years.

The outside begins to move in through this window.

Interestingly, ex-workers at the toxic gas reactor have said that even they were not aware of the names of the gases they were making and spoke about them only by their colors. When the working men of the island were drafted into the military in 1944, more than 1,000 children, who could be as young as 14, were brought into the plant to replace them.


On Okunoshima, rabbits are protected from pets such as cats and dogs.

The child laborers were exposed to the toxic materials too, through hazardous tasks such as storing the shells containing the poison gas and cleaning up the facility itself. According to Yamauchi Masayuki, one of the leaders of an organization that runs tours of the facilities, many of them became sick and suffered from ill health for the rest of their lives. Occasionally there were also accidents at the plant, or workers became disfigured through exposure to the arsenic in the mustard gas, which produced bubbles under their skin.

The ruins of a place responsible for the illness and maybe even death of many.

After World War II, the Japanese attempted to hide all evidence of the chemical weapons plant on Okunoshima. Documents were burned and machinery was broken up. As part of the Allied Occupation of Japan, American and then British and Australian troops landed on the island. And despite the Japanese army’s efforts to conceal the existence of the plant, the Americans discovered nearly 5,000 tons of toxic gas, which they dumped into the ocean.


This was once the power generator building.

The Americans also questioned those in charge of the island’s chemicals weapons program, but kept the information gleaned classified, and nobody responsible was ever charged. It should be noted that, at the time, the USA was forging ahead with its own biological weapons program in secret. There were even some within the American military who had advocated using chemical warfare when invading Japan.

One of the prime attractions on the island these days

It was not only Okunoshima that was left with a mess to clean up after the war. According to the Chinese, the Japanese left two million poison gas shells behind in munitions dumps when they left China. It was not until 1995 that the Japanese government admitted responsibility for the abandoned toxic weapons as well as their clean-up.


View from a high point on the island

These days, Okunoshima’s wild rabbit population is one of its main draws. The bunnies have taken over the island and are said to be the descendants of a group of rabbits let loose by a primary school in 1971. These bunnies have a much better life than those used to test the poison gas at the plant. All of those animals died when the factory was destroyed.

The sun comes in through two broken factory windows.

The island also features a campsite, a small golf course, a swimming pool, tennis courts, and a hotel. As well as feeding and petting the rabbits, visitors can swim and snorkel at the beaches or ride bikes and take walks along the island roads. Okunoshima reportedly has around 100,000 annual visitors.


Rabbits graze among the ruins.

The locals don’t try to conceal the island’s dark history, however. In fact, they have built a museum there dedicated to telling the story of the gas plant and the lives it affected. It is not a large building, containing only two rooms, but it displays factory equipment, some of the weapons produced, and even diaries of the workers. There are also more recent photographs of victims of chemical weapons – so that their horrific effects can be seen.

A tunnel leads to a plant building.

The museum and ruins of Okunoshima’s poisonous gas facility are a reminder of some of the worst acts committed during WWII. And not far away is the city of Hiroshima, the site of another great atrocity. “My hope is that people will see the museum in Hiroshima City and also this one, so they will learn that we were both victims and aggressors in the war,” the museum’s curator and ex-plant worker, Hatsuichi Murakami, told The New York Times. “I hope people will realize both facets and recognize the importance of peace.”

Sources: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18