When the first atomic bomb detonated 80 years ago on August 6, thousands of the dead and dying were brought to the small, rural island of Ninoshima, just south of Hiroshima, by military boats with crews that had trained for suicide attack missions.

Owing to inadequate medical care, only a few hundred were alive when the field hospital closed on August 25, according to historical records. They were buried in various locations in chaotic and rushed operations.

Decades later, people in the area are searching for the remains of the missing, driven by a desire to account for and honour the victims, and to bring relief to survivors who are still tormented by memories of missing loved ones.

“Until that happens, the war is not over for these people,” said Rebun Kayo, a Hiroshima University researcher who regularly visits Ninoshima to search for remains.

On a recent morning, Kayo visited a hillside plot in the forest where he has been digging for remains since 2018. He put on rubber boots and a helmet, and sprayed insect repellent.

After planting chrysanthemum flowers and praying, Kayo carefully began shovelling gravel from a hole the size of a bathtub. When the soil was soft enough, he sifted it for bone fragments.

So far, Kayo has found about 100 bone fragments, including pieces of skull and an infant’s jawbone with small teeth attached. He found the bones in an area suggested by a Ninoshima resident whose father had witnessed soldiers burying bodies that were brought to the island by boat from Hiroshima 80 years ago.

The US atomic attack on Hiroshima instantly destroyed the city and killed tens of thousands near the hypocentre, about 10km (6 miles) north of Ninoshima. The death toll by the end of that year was 140,000.

Within two hours of the blast, victims began arriving by boat from Hiroshima at the island’s Number 2 quarantine centre. Its buildings filled with patients suffering severe wounds. Many died en route to the island.

Eiko Gishi, then an 18-year-old boat trainee, oversaw carrying patients from the pier to the quarantine area for first aid. He and other soldiers cut bamboo to make cups and trays.

In recollections published by the city years later, Gishi wrote that soldiers initially handled bodies carefully, one by one, but were soon overwhelmed by the huge number of decomposing corpses and used an incinerator originally intended for military horses.

Even this was not enough, and they soon ran out of space, eventually placing bodies in bomb shelters and burial mounds.

“I was speechless from the shock when I saw the first group of patients that landed on the island,” a former army medic, Yoshitaka Kohara, wrote in 1992.

“I was used to seeing many badly wounded soldiers on battlefields, but I had never seen anyone in such a cruel and tragic state,” he said. “It was an inferno.”

Kohara remained at the facility until its closure, when only about 500 people were left alive. When he told the surviving patients that the war had ended on August 15, he recalled that they looked emotionless: “Tears flowed from their crushed eyes, and nobody said a word.”

Kazuo Miyazaki, a Ninoshima-born historian and guide, said that towards the end of World War II, the island was used to train suicide attackers using wooden boats meant for deployment in the Philippine Sea and Okinawa.

Miyazaki, 77, lost a number of relatives in the atomic bombing. He has heard firsthand stories from relatives and neighbours about what happened on Ninoshima, which was home to a major army quarantine centre during Japan’s period of militarist expansion. His mother was an army nurse who was deployed to the field hospital on the island.

The remains of about 3,000 atomic bombing victims brought to Ninoshima have been found since 1947, when many were dug out of bomb shelters.

Thousands more are thought to be missing.