(CNN) A battered tricycle. Melted coins. A shredded shirt. Seventy years have passed, but artifacts and survivors still provide tangible links to the world's first act of nuclear warfare.

The world still struggles to fully understand the hellish events in Hiroshima, Japan, on August 6, 1945, after a U.S. warplane dropped the most powerful weapon ever produced on military targets and unsuspecting civilians.

Those who survived say it started with a brilliant, noiseless flash. They remember a massive wave of intense heat that turned clothing to rags. People closest to the bomb were immediately vaporized or burned to ashes. There was a deafening boom and a blast that -- for some -- felt like being stabbed by hundreds of needles.

Soldiers and sailors on the USS Missouri watch as Japan's formal surrender is signed in Tokyo Bay on September 2, 1945.

Soldiers and sailors on the USS Missouri watch as Japan's formal surrender is signed in Tokyo Bay on September 2, 1945.

A woman and a child walk in Nagasaki on the day of the bombing. More than 70,000 people there were killed instantly.

A woman and a child walk in Nagasaki on the day of the bombing. More than 70,000 people there were killed instantly.

Survivors of the Nagasaki bomb walk through the destruction as fire rages in the background.

Survivors of the Nagasaki bomb walk through the destruction as fire rages in the background.

This photo was taken about six miles from the scene of the Nagasaki explosion. According to the Nagasaki Atomic Bomb Museum, photographer Hiromichi Matsuda took this photograph 15 minutes after the attack.

This photo was taken about six miles from the scene of the Nagasaki explosion. According to the Nagasaki Atomic Bomb Museum, photographer Hiromichi Matsuda took this photograph 15 minutes after the attack.

A worker stands next to an atomic bomb, nicknamed "Fat Man," hours before it was dropped on Nagasaki, Japan, on August 9, 1945.

A worker stands next to an atomic bomb, nicknamed "Fat Man," hours before it was dropped on Nagasaki, Japan, on August 9, 1945.

A white silhouette on a Hiroshima bridge shows an area that wasn't scorched by the bomb. It was reportedly the outline of a person's shadow -- someone who was shielded from the blast's heat rays by another person.

A white silhouette on a Hiroshima bridge shows an area that wasn't scorched by the bomb. It was reportedly the outline of a person's shadow -- someone who was shielded from the blast's heat rays by another person.

U.S. President Harry Truman, aboard a U.S. Navy cruiser, reads reports of the Hiroshima bombing. Eight days earlier, Truman had warned Japan that the country would be destroyed if it did not surrender unconditionally.

U.S. President Harry Truman, aboard a U.S. Navy cruiser, reads reports of the Hiroshima bombing. Eight days earlier, Truman had warned Japan that the country would be destroyed if it did not surrender unconditionally.

An aerial photograph of Hiroshima shortly after the atomic bomb, nicknamed "Little Boy," was dropped.

An aerial photograph of Hiroshima shortly after the atomic bomb, nicknamed "Little Boy," was dropped.

Air Force Col. Paul Tibbetts waves from the pilot's seat of the Enola Gay moments before takeoff on August 6, 1945. A short time later, the plane's crew dropped the first atomic bomb in combat, instantly killing 80,000 people in Hiroshima.

Air Force Col. Paul Tibbetts waves from the pilot's seat of the Enola Gay moments before takeoff on August 6, 1945. A short time later, the plane's crew dropped the first atomic bomb in combat, instantly killing 80,000 people in Hiroshima.

Trinity was the code name of the test bomb, which was detonated in the Jornada del Muerto desert.

Trinity was the code name of the test bomb, which was detonated in the Jornada del Muerto desert.

Workers in New Mexico attach a bomb to a tower two days before its successful test in July 1945.

Workers in New Mexico attach a bomb to a tower two days before its successful test in July 1945.

The Manhattan Project also involved research facilities in Oak Ridge, Tennessee, and Hanford, Washington. Billboards, like this one in Oak Ridge, reminded workers of the project's top-secret nature.

The Manhattan Project also involved research facilities in Oak Ridge, Tennessee, and Hanford, Washington. Billboards, like this one in Oak Ridge, reminded workers of the project's top-secret nature.

Los Alamos workers pose on a platform stacked with 100 tons of TNT. It was to be used to gauge radioactive fallout.

Los Alamos workers pose on a platform stacked with 100 tons of TNT. It was to be used to gauge radioactive fallout.

In 1942, U.S. Army Col. Leslie R. Groves, left, was appointed to head the Manhattan Project. On the right is physicist J. Robert Oppenheimer, who led the Los Alamos National Laboratory in New Mexico.

In 1942, U.S. Army Col. Leslie R. Groves, left, was appointed to head the Manhattan Project. On the right is physicist J. Robert Oppenheimer, who led the Los Alamos National Laboratory in New Mexico.

In 1939, physicists Albert Einstein, left, and Leo Szilard drafted a letter to U.S. President Franklin D. Roosevelt, urging him to research atomic bombs before the Germans could build one first. By 1942, the United States had approved the top-secret Manhattan Project to build a nuclear reactor and assemble an atomic bomb.

In 1939, physicists Albert Einstein, left, and Leo Szilard drafted a letter to U.S. President Franklin D. Roosevelt, urging him to research atomic bombs before the Germans could build one first. By 1942, the United States had approved the top-secret Manhattan Project to build a nuclear reactor and assemble an atomic bomb.

The United States detonates the world's first atomic bomb at a test site in New Mexico on July 16, 1945. Less than a month later, atomic bombs were dropped on the Japanese cities of Hiroshima and Nagasaki. The devastation led to Japan's unconditional surrender and brought an end to World War II.

The United States detonates the world's first atomic bomb at a test site in New Mexico on July 16, 1945. Less than a month later, atomic bombs were dropped on the Japanese cities of Hiroshima and Nagasaki. The devastation led to Japan's unconditional surrender and brought an end to World War II.

Then the fires started. Tornadoes of flames swept through the city. Many survivors found themselves covered with blisters. Bodies littered the streets.

It got worse. It began to rain. Sticky, radioactive raindrops blackened everything they touched and were hard to wash off.

It's estimated that at least 70,000 people died in the hours immediately following the blast. Later, radiation sickness, cancer and other long-term effects pushed the estimated death toll above 200,000, according to the U.S. Department of Energy

Drawings

The drawings depict haunting memories. In one drawing, a mother is screaming her child's name while looking down at a river full of dead children.

Another rendering shows a pair of students with swollen blue faces.

An exodus of wounded survivors is depicted in another drawing. They're seen packed into rail cars like cattle.

Each drawing reveals glimpses of that horrific day, reflected through the prism of a survivor's personal struggle to stay alive.

Photos: Drawings show haunting memories of Hiroshima Photos: Drawings show haunting memories of Hiroshima The Hiroshima Peace Memorial Museum has collected thousands of drawings made by survivors of the atomic bombing of Hiroshima, Japan. The drawings document survivors' memories surrounding that horrible day. In this rendering, Hideo Kimura shows burned and screaming classmates. Some were trapped under heavy gates and houses. Others were in the river, holding onto a stone embankment. Hide Caption 1 of 13 Photos: Drawings show haunting memories of Hiroshima This drawing by survivor Akira Onogi shows a woman pinned under a pillar from her collapsed house as deadly flames approach. Next to the woman, a sobbing girl pleads for help from neighbors. The neighbors couldn't move the pillar. Hide Caption 2 of 13 Photos: Drawings show haunting memories of Hiroshima Chisako Sasaki drew this image of a girl at a window on the second floor of a burning house. Sasaki remembers the girl crying for help. "I can never forget," Sasaki said. Hide Caption 3 of 13 Photos: Drawings show haunting memories of Hiroshima Mitsuko Taguchi is haunted by this scene, depicted in her drawing, of a dead mother and child who had fallen while trying to outrun flames. "Her hair was standing on end," Taguchi said. "She still protected her child under her breast, like a living person. Her eyes were open wide. I cannot forget that shocking sight." Hide Caption 4 of 13 Photos: Drawings show haunting memories of Hiroshima Torazuchi Matsunaga remembered soldiers carrying children's corpses on stretchers to a temporary crematorium. "These children had been injured by the bomb and taken to the army hospital for treatment but had soon died," she said. "The hands and legs sticking out of the stretcher swung with the motion. My chest suddenly seized with emotion." Hide Caption 5 of 13 Photos: Drawings show haunting memories of Hiroshima Survivor Asako Fujise drew this image of a bomb shelter that was being used as a makeshift hospital. It was "filled with moans and the smell of zinc oxide and Mercurochome mixed with sweat." Hide Caption 6 of 13 Photos: Drawings show haunting memories of Hiroshima Sueko Sumimoto remembered a mother standing on a bridge. She was screaming her child's name while the bodies of dead students floated on the river below. Hide Caption 7 of 13 Photos: Drawings show haunting memories of Hiroshima Hiroharu Kono drew a picture of her search for missing family members. Three days after the bombing, she arrived at where her house once stood. "Fires were still burning here and there, and the streets were so hot I could hardly get through," she said. After digging through a foot of dirt, Kono found the bones of her older brother, older sister and a 3-day-old baby who had all died in a fire. "I put my hands together and just prayed to Namu Amida Buddha," she said. "I wept and wept." Hide Caption 8 of 13 Photos: Drawings show haunting memories of Hiroshima Not all the drawings depict bad memories. Masaru Shimizu remembers being given a few dozen frozen mandarin oranges by the military. "I gave some of them to relatives who were seriously injured by the atomic bomb," she said. Hide Caption 9 of 13 Photos: Drawings show haunting memories of Hiroshima Soldiers had been trained not to give water to burn victims, thinking it would worsen their condition. Keiji Harada remembers girls asking her for water. "While I was rushing to get them water, a military policeman yelled at me to stop. When I remember, I deeply regret that I obeyed. I should have found a way to help them." Hide Caption 10 of 13 Photos: Drawings show haunting memories of Hiroshima The memory of seeing two girls with blue-violet faces shocked Torao Izuhara so much that she never forgot it. Their faces were "swollen so badly that you couldn't tell whether their eyes were open or shut, and their skirts were ripped up right at the creases," Isuhara said. "Their faces were really even blacker than the drawing. They helped each other walk along, their shoulders joined together, their powerless legs somehow carrying them off towards the Otagawa River." Hide Caption 11 of 13 Photos: Drawings show haunting memories of Hiroshima Like cattle, injured survivors were loaded into rail cars to escape the ruined city. "Most people were injured, and those with burns were slathered with white medicine," Kazuo Koya said. "There were so many bandaged people. With only the clothes on their backs, they waited under the blazing sun for departure." Hide Caption 12 of 13 Photos: Drawings show haunting memories of Hiroshima Sumie Sasaki was fortunate enough to find a bit of beauty amid all the horror. "The stars were beautiful," she recalled. "My father gathered charred tin sheeting and broken planks and built us a shack over the burnt ruins of his company. One plant's tall smokestack remained standing, and it scared us at night. But the stars glittering all around the scary smokestack were so beautiful." Hide Caption 13 of 13

Artifacts

The artifacts range from the poignant to the bizarre: a blackened Shirley Temple doll brought from America, a clump of coins fused together by the blast's intense heat.

The story behind one artifact was published as a children's book by survivor Tatsuharu Kodama in 1995. "Shin's Tricycle" tells what happened to a 3-year-old boy named Shinichi Tetsutani.

It's narrated by Shin's father, Nobuo Tetsunani, who describes the morning shortly before the attack as a calm and sunny day. "The air was filled with the sandpapery sounds of cicadas rubbing their legs together in the nearby trees," the book said.

Shin and his best friend, a girl named Kimi, were outside the family's home, playing with his favorite toy -- a tricycle with red handlebars.

At 8:15 a.m., the bomb detonated. And everything changed.

The blast collapsed the house, creating an "explosion so terrible, a flash so blindingly bright. I thought the world had ended," the boy's father said in the book. "Then, just a quickly, everything went black."

Shin was missing in the chaos immediately following the attack. His family frantically searched for him among the wreckage of his destroyed home. They found Shin pinned under a house beam, badly hurt. "His face was bleeding and swollen," the book reads. "He was too weak to talk but his hand still held the red handlebar grip from his tricycle. Kimi was gone, lost somewhere under the house."

The family joined other neighborhood survivors along a nearby riverbank. "It was a horrible sight," the book said. "Everyone was burned, and they were crying moaning and screaming for water."

"'Water, I want water,' pleaded Shin in a faint voice. I wanted to help him so much," his father said in the book.

"All around, people were dying when they drank water," Shin's father said. "So I didn't dare give him any."

Shin would not survive the night.

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After his son died, Shin's father couldn't bare to leave the boy's body in a lonely graveyard. So the family buried Shin in their backyard, along with his friend Kimi and his beloved tricycle.

In 1985, 40 years later, Shin's father decided to move his son's remains to the family gravesite. He and Kimi's mother helped unearth the backyard grave. There, according to the book, they saw "the little white bones of Kimi and Shin, hand in hand as we had placed them."

Shin's father had all but forgotten about the tricycle. But there it was.

Lifting it out of the grave, he said: "This should never happen to children. The world should be a peaceful place where children can play and laugh."

The next day Shin's father donated the trike to the museum.

There, the legacy of a 3-year-old boy continues to remind future generations of the horrors of nuclear destruction.