Seventy years after the Castle Bravo nuclear test took place on Bikini Atoll, Setsuko Shimomoto will travel to the Marshall Islands to take part in a memorial event for an atomic experiment that she believes killed her father.
The test, on March 1, 1954, was significantly larger than what the scientists who developed the hydrogen bomb had anticipated. To this day, Castle Bravo remains the most powerful nuclear device ever detonated by the US military.
The failure to anticipate the size of the blast, combined with strong winds in the central Pacific, meant that radioactive fallout fell across a vast swathe of the ocean,and over around 1,000 Japanese fishing boats in the area.
The most famous boat affected by the fallout was the Daigo Fukuryu Maru, or the Lucky Dragon 5, whose 23-strong crew suffered a range of complaints linked to exposure to radiation, including nausea, headaches and pain in their eyes. One of the men, radioman Aikichi Kuboyama, died six months later from complications linked to exposure to radiation.
The story of Toubei Oguro
The Lucky Dragon is now displayed in a museum in Tokyo. However, the other Japanese fishing boats in the area, which carried around 10,000 sailors, have largely been forgotten, and Shimomoto wants to change that.
"I feel that it is important for me to go to the Marshall Islands as this is the 70th anniversary and, 10 years ago, Matashichi Oishi of the Lucky Dragon participated in the ceremony and gave a speech," Shimomoto told DW.
"I want to convey the fear of radiation," she said. "I also want all states in the world to join the Nuclear Weapons Convention, which bans the development, possession, use, threat and transfer of nuclear weapons."
More broadly, Shimomoto aims to encourage support for the citizens of Hiroshima and Nagasaki who survived the 1945 atomic bombs. She also wants to win support for a series of legal cases brought by Japanese fishermen or their surviving families against the Japanese government for compensation and assistance for their medical complaints.
US paid 'consolation money'
Shimonoto's father, Toubei Oguro, was a 30-year-old fisherman aboard the Japanese tuna boat, the Dai-Nana Dai Maru, when the Castle Bravo device detonated at 6.45 am local time on a man-made platform in Bikini Atoll. Six years later, his seaman's logbook says he was laid off due to an unspecified illness.
At the age of 60, Oguro underwent an operation that removed three-quarters of his stomach due to cancer, but it was only after his death in 2002, at the age of 78, that comprehensive medical examinations of the rest of the crew of the Dai-Nana Dai Maru and the other vessels that were operating off Bikini atoll in 1954 were carried out.
The tests confirmed chromosomal abnormalities, although the fishermen's efforts to win recognition and compensation for their medical complaints has not been forthcoming.
In 1955, the United States paid Japan $2 million in "consolation money" but refused to admit liability, concluding the issue at the political level.
The Japanese government paid each of the crew of the Lucky Dragon 2 million yen ($12,278 at present-day exchange rates) but provided nothing to fishermen aboard other ships. Critics say Tokyo was keen to bury the issue as swiftly as possible to avoid antagonizing the US.
Japan argues exposure 'not damaging to health'
The health ministry in Tokyo admitted that crew members of 10 ships were exposed to radiation, but it insisted that their doses "did not reach levels that could damage their health."
The matter was largely left to languish until the 1985, when students from a school in Kochi Prefecture — where many of the tuna ships that had been exposed to the Castle Bravo and other tests were based — interviewed fishermen as part of a school project.
Local and then national media caught wind of the sailors' stories, prompting many to raise questions. Requests to the Ministry of Health and Welfare for details on the impact of the radiation on the fishermen were rejected. The ministry insisted that documents compiled at the time no longer existed.
In response to a series of legal challenges, however, bureaucrats finally admitted in September 2014 that they did have the data.
The lengthy delay in handing over the paperwork prevented the fishermen from launching legal challenges for compensation from the US. They claim the Japanese government deliberately withheld the information.
Two lower courts initially dismissed lawsuits brought by 31 plaintiffs on the grounds that the 20-year statute of limitations in the case had expired. The plaintiffs disagreed with the rulings, pointing out that the government had withheld vital evidence from them. The courts replied that the government had not intentionally concealed the data and stuck to their rulings.
Masayoshi Naito, a lawyer with the Higashi Kanda Law Office in Tokyo, is representing a dwindling number of plaintiffs in the appeals case.
"We have to remember that this came soon after the cease-fire in the Korean War and the official inauguration of the People's Republic of China [in 1949], and there was concern after the Lucky Dragon incident would encourage the anti-nuclear movement in Japan," Naito said.
'Cover-up by US, Japan'
"The US and Japanese governments tried to cover up what happened in the Marshall Islands," Naito said, adding that it was easier to do that under the cover of national security and because many of the fishermen who had been exposed to radiation only began showing symptoms many years later.
The fishermen did not initially protest loudly as they feared ostracism in Japanese society and that their livelihoods would be endangered, he added.
Naito has appealed lower court rulings in 2019 demanding that the government-run seafarers' insurance scheme cover their health costs.
With the case now due to be heard in Tokyo, Naito admits it "will not be easy" to sway the judges. But he believes the case will hinge on "how the court reacts to the government's cover-up of the facts."
Shimomoto will use her trip to the Marshall Islands to promote her anti-nuclear message.
"Japan has still not joined the Nuclear Weapons Convention," she pointed out. "This is a treaty that should be obvious to everyone. I hope that all countries join this treaty so that nuclear weapons and the damage they can cause are eliminated from the Earth. And I want those who have been suffering to receive relief."