As a survivor of history’s deadliest atomic bombing, Setsuko Thurlow has a powerful case to make against nuclear weapons.

On the morning of August 6, 1945, the 13-year-old Thurlow reported to a military office in Hiroshima, along with other girls recruited to help with Japan’s wartime code breaking. While listening to an officer speak, she saw a burst of light out the window, and was hit with a blast that catapulted her through the air. When she came to, she was pinned under parts of the building she’d been in.

Thurlow is one of the survivors of the U.S. atomic bombing of Hiroshima at the end of World War II that killed an estimated 90,000 to 120,000 people, according to the journal Science. The military office she worked in stood less than two miles from where the bomb hit. Three days later, the United States dropped a second atomic bomb on Nagasaki, killing another 60,000 to 70,000 people.

The two attacks left hundreds of thousands of survivors with physical injuries, lasting health problems and severe trauma. Over the next several decades, some of these “hibakusha,” or people affected by the bomb, became vocal activists, criss-crossing the world to condemn the weapons that had so drastically altered their lives. Together, they helped to introduce a major United Nations treaty, an effort that garnered the 2017 Nobel Peace Prize.

Thurlow began speaking publicly against nuclear weapons as early as 1954, when she came to the United States to attend a university in Virginia. Local reporters asked for her reaction to U.S. hydrogen bomb testing in the Pacific that had killed a Japanese fisherman by giving him radiation poisoning.

“I feel angry,” she said. When her response appeared in a newspaper, she started receiving hate mail telling her to go back to Japan, or asserting that Japan had deserved the bombing.

Stunned by the backlash, Thurlow resolved to speak out about the horrific effects of nuclear weapons—and call for their elimination. “As a survivor of Hiroshima, it was my moral responsibility to keep telling the world about it so that knowledge could prevent a similar thing from happening again,” she said.

Now age 90, she has told her story in venues all over the world, recalling how when she escaped from the rubble of the building that day, she saw people with their skin hanging off and organs falling out. Several of her family members died, both from the initial blast and the radiation sickness it unleashed.

Sharing these details with the world can be incredibly painful for hibakusha. For one of the Nagasaki bombing survivors who became an anti-nuclear weapons activist, telling his story involved sharing graphic pictures of how the bomb maimed him.

Sumiteru Taniguchi was 16 years old on August 9, 1945, the day the United States dropped an atomic bomb on Nagasaki. He was delivering mail on his bicycle in the city when the bomb hit. The blast threw him to the ground and stripped the skin from his back. He was in a hospital for more than three and a half years, two of which he spent lying on his stomach as doctors tried to treat his injuries and the resulting infections.

Over the next several decades, Taniguchi—who died of cancer in 2017 at age 88—used his personal story to argue for the elimination of nuclear weapons. At a 2010 United Nations conference on nuclear arms, he held up graphic pictures of what the atomic bomb had done to his back to make his point.

Thurlow, Taniguchi and other hibakusha have played an important role in advocating for the Treaty on the Prohibition of Nuclear Weapons. The United Nations adopted the treaty a month before Taniguchi’s death in 2017. Later that year, Thurlow accepted the Nobel Peace Prize on behalf of the International Campaign to Abolish Nuclear Weapons.

As of 2023, 68 sovereign states have signed and ratified the UN treaty or acceded to it after it went into effect in 2021. Prominent hibakusha have criticized the United States and the eight other nuclear powers for refusing to sign the treaty. Thurlow has also criticized Japan, which has no nuclear weapons, for not signing the treaty in order to appease the United States.

As first-hand witnesses to the horrors of nuclear weapons, hibakusha have been powerful voices in the anti-nuclear arms movement. In October 2024, Nihon Hidankyo, a grassroots movement of Hiroshima and Nagasaki survivors, were awarded the Nobel Peace Prize. "The hibakusha help us to describe the indescribable, to think the unthinkable, and to somehow grasp the incomprehensible pain and suffering caused by nuclear weapons," the Nobel committee said. As this population ages, many activists—including hibakusha themselves—have expressed worry about a near future in which these survivors are no longer around to remind the world of why atomic weaponry poses such a grave threat to the world.

In 2017, the anti-nuclear arms movement lost both Taniguchi and 100-year-old Shuntaro Hida, a doctor who survived the Hiroshima attack, helped treat other victims and spoke internationally about the impact of nuclear weapons. In 2021, the activist Sunao Tsuboi, who was a university student in Hiroshima when the bomb hit, died at age 96.

“I am worried about what will happen to the world,” Taniguchi said before his own death, “when there are no more atomic bomb survivors.”