Korean and Chinese workers, prisoners of war, and mobilized adults and students had returned to their work sites; some dug or repaired shelters, others piled sandbags against the windows of City Hall for protection against machine-gun fire. In the Mitsubishi sports field, bamboo spear drills in preparation for an invasion had just concluded. Classes had resumed at Nagasaki Medical College. Streetcars meandered through the city.

Hundreds of people injured in the air raids just over a week earlier continued to be treated in Nagasaki’s hospitals, and at the tuberculosis hospital in the northern Urakami Valley, staff members served a late breakfast to their patients. One doctor, trained in German, thought to himself, Im Westen nichts neues (All quiet on the western front). In the concrete-lined shelter near Suwa Shrine that served as the Nagasaki Prefecture Air Defense Headquarters, Governor Nagano had just begun his meeting with Nagasaki police leaders about an evacuation plan. The sun was hot, and the high-pitched, rhythmic song of cicadas vibrated throughout the city.

Six miles above, the two B-29s approached Nagasaki. Major Sweeney and his crew could hardly believe what they saw: Nagasaki, too, was invisible beneath high clouds. This presented a serious problem. Sweeney’s orders were to drop the bomb only after visual sighting of the aiming point — the center of the old city, east of Nagasaki Harbor. Now, however, a visual sighting would likely require numerous passes over the city, which was no longer possible due to fuel loss: Not only had a fuel transfer pump failed before takeoff, rendering six hundred gallons of fuel inaccessible, but more fuel than expected had been consumed waiting at the rendezvous point and while circling over Kokura.

Bockscar now had only enough fuel to pass over Nagasaki once and still make it back for an emergency landing at the American air base on Okinawa. Further, Sweeney and his weaponeer, Navy commander Fred Ashworth, knew that not using the bomb on Japan might require dumping it into the sea to prevent a nuclear explosion upon landing. Against orders, they made the split-second decision to drop the bomb by radar.

Air raid alarms did not sound in the city — presumably because Nagasaki’s air raid defense personnel did not observe the planes in time or did not recognize the immediate threat of only two planes flying at such a high altitude. When antiaircraft soldiers on Mount Kompira finally spotted the planes, they jumped into trenches to aim their weapons but didn’t have time to fire; even if they had, their guns could not have reached the U.S. planes.

Several minutes earlier, some citizens had heard a brief radio announcement that two B-29s had been seen flying west over Shimabara Peninsula. When they heard the planes approaching, or saw them glistening high in the sky, they called out to warn others and threw themselves into air raid shelters, onto the ground, or beneath beds and desks inside houses, schools, and workplaces. A doctor just about to perform a pneumothorax procedure heard the distant sound of planes, pulled the needle out of his patient, and dived for cover. Most of Nagasaki’s residents, however, had no warning.

By this time, the crews on both planes were wearing protective welders’ glasses so dark that they could barely see their own hands. Captain Kermit Beahan, Bockscar’s bombardier, activated the tone signal that opened the bomb bay doors and indicated 30 seconds until release. Five seconds later, he noticed a hole in the clouds and made a visual identification of Nagasaki.

“I’ve got it! I’ve got it!” he yelled. He released the bomb. The instrument plane simultaneously discharged three parachutes, each attached to metal canisters containing cylindrical radiosondes to measure blast pressure and relay data back to the aircraft. Ten thousand pounds lighter, Bockscar lurched upward, the bomb bay doors closed, and Sweeney turned the plane an intense 155 degrees to the left to get away from the impending blast.

“Hey, Look! Something’s Falling!”

On the ground below, 18-year-old Wada had just arrived at Hotarujaya Terminal at the far eastern corner of the old city.

Nagano was at work in the temporary Mitsubishi factory in Katafuchimachi, on the other side of the mountains from her family’s home.

Taniguchi was delivering mail, riding his bicycle through the hills of a residential area in the northwestern corner of the city.

Sixteen-year-old Do-oh was back at her workstation inside the Mitsubishi weapons factory, inspecting torpedoes and eagerly awaiting her lunch break.

On the side of a road on the western side of the Urakami River, Yoshida was lowering a bucket into the well when he looked up and, like others across the city, noticed parachutes high in the sky, descending through a crack in the clouds.

“Rakka–san, they were called back then,” he remembered. Descending umbrellas. “I just thought that they were regular parachutes — that maybe soldiers were coming down.”

“Hey, look! Something’s falling!” he called out to his friends. They all looked up, putting their hands to their foreheads to block the sun so they could see.

“The parachutes floated down, saaatto,” he said. Quietly, with no sound.

A Deafening Roar

The five-ton plutonium bomb plunged toward the city at 614 miles per hour. Forty-seven seconds later, a powerful implosion forced its plutonium core to compress from the size of a grapefruit to the size of a tennis ball, generating a nearly instantaneous chain reaction of nuclear fission. With colossal force and energy, the bomb detonated a third of a mile above the Urakami Valley and its 30,000 residents and workers, a mile and a half north of the intended target. At 11:02 a.m., a superbrilliant flash lit up the sky — visible from as far away as Omura Naval Hospital more than 10 miles over the mountains — followed by a thunderous explosion equal to the power of 21,000 tons of TNT. The entire city convulsed.

At its burst point, the center of the explosion reached temperatures higher than at the center of the sun, and the velocity of its shock wave exceeded the speed of sound. A tenth of a millisecond later, all of the materials that had made up the bomb converted into an ionized gas, and electromagnetic waves were released into the air. The thermal heat of the bomb ignited a fireball with an internal temperature of over 540,000 degrees Fahrenheit. Within one second, the blazing fireball expanded from 52 feet to its maximum size of 750 feet in diameter. Within three seconds, the ground below reached an estimated 5,400 to 7,200 degrees Fahrenheit. Directly beneath the bomb, infrared heat rays instantly carbonized human and animal flesh and vaporized internal organs.

As the atomic cloud billowed two miles overhead and eclipsed the sun, the bomb’s vertical blast pressure crushed much of the Urakami Valley. Horizontal blast winds tore through the region at two and a half times the speed of a category five hurricane, pulverizing buildings, trees, plants, animals, and thousands of men, women, and children. In every direction, people were blown out of their shelters, houses, factories, schools, and hospital beds; catapulted against walls; or flattened beneath collapsed buildings.

Those working in the fields, riding streetcars, and standing in line at city ration stations were blown off their feet or hit by plummeting debris and pressed to the scalding earth. An iron bridge moved 28 inches downstream. As their buildings began to implode, patients and staff jumped out of the windows of Nagasaki Medical College Hospital, and mobilized high school girls leaped from the third story of Shiroyama Elementary School, a half mile from the blast.

The blazing heat melted iron and other metals, scorched bricks and concrete buildings, ignited clothing, disintegrated vegetation, and caused severe and fatal flash burns on people’s exposed faces and bodies. A mile from the detonation, the blast force caused nine-inch brick walls to crack, and glass fragments bulleted into people’s arms, legs, backs, and faces, often puncturing their muscles and organs. Two miles away, thousands of people suffering flesh burns from the extreme heat lay trapped beneath partially demolished buildings.

At distances up to five miles, wood and glass splinters pierced through people’s clothing and ripped into their flesh. Windows shattered as far as eleven miles away. Larger doses of radiation than any human had ever received penetrated deeply into the bodies of people and animals. The ascending fireball suctioned massive amounts of thick dust and debris into its churning stem. A deafening roar erupted as buildings throughout the city shuddered and crashed to the ground.

“The Light Was Indescribable”

“It all happened in an instant,” Yoshida remembered. He had barely seen the blinding light half a mile away before a powerful force hit him on his right side and hurled him into the air. “The heat was so intense that I curled up like surume [dried grilled squid].” In what felt like dreamlike slow motion, Yoshida was blown backward 130 feet across a field, a road, and an irrigation channel, then plunged to the ground, landing on his back in a rice paddy flooded with shallow water.

Inside the Mitsubishi Ohashi weapons factory, Do-oh had been wiping perspiration from her face and concentrating on her work when PAAAAAHT TO! — an enormous blue-white flash of light burst into the building, followed by an earsplitting explosion. Thinking a torpedo had detonated inside the Mitsubishi plant, Do-oh threw herself onto the ground and covered her head with her arms just as the factory came crashing down on top of her.

In his short-sleeved shirt, trousers, gaiters, and cap, Taniguchi had been riding his bicycle through the hills in the northwest corner of the valley when a sudden burning wind rushed toward him from behind, propelling him into the air and slamming him facedown on the road. “The earth was shaking so hard that I hung on as hard as I could so I wouldn’t get blown away again.”

Nagano was standing inside the school gymnasium-turned-airplane-parts factory, protected to some degree by distance and the wooded mountains that stood between her and the bomb. “A light flashed — pi-KAAAAH!” she remembered. Nagano, too, thought a bomb had hit her building. She fell to the ground, covering her ears and eyes with her thumbs and fingers according to her training as windows crashed in all around her. She could hear pieces of tin and broken roof tiles swirling and colliding in the air outside.

Two miles southeast of the blast, Wada was sitting in the lounge of Hotarujaya Terminal with other drivers, discussing the earlier derailment. He saw the train cables flash. “The whole city of Nagasaki was — the light was indescribable — an unbelievably massive light lit up the whole city.” A violent explosion rocked the station. Wada and his friends dived for cover under tables and other furniture. In the next instant, he felt like he was floating in the air before being slapped down on the floor. Something heavy landed on his back, and he fell unconscious.

Beneath the still-rising mushroom cloud, a huge portion of Nagasaki had vanished. Tens of thousands throughout the city were dead or injured. On the floor of Hotarujaya Terminal, Wada lay beneath a fallen beam. Nagano was curled up on the floor of the airplane parts factory, her mouth filled with glass slivers and choking dust. Do-oh lay injured in the wreckage of the collapsed Mitsubishi factory, engulfed in smoke. Yoshida was lying in a muddy rice paddy, barely conscious, his body and face brutally scorched. Taniguchi clung to the searing pavement near his mangled bicycle, not yet realizing that his back was burned off. He lifted his eyes just long enough to see a young child “swept away like a fleck of dust.”

Sixty seconds had passed.

“A Huge, Boiling Caldron”

The enormous, undulating cloud ascended seven miles above the city. From the sky, Bockscar’s copilot Lieutenant Frederick Olivi described it as “a huge, boiling caldron.” William L. Laurence, the official journalist for the Manhattan Project who had witnessed the bombing from the instrument plane, likened the burgeoning cloud to “a living thing, a new species of being, born right before our incredulous eyes.” Captain Beahan remembered it “bubbling and flashing orange, red and green… like a picture of hell.”

Outside the city, many people who saw the flash of light and heard the deafening explosion rushed out of their homes and stared in wonder at the nuclear cloud heaving upward over Nagasaki. A worker on an island in Omura Bay, several miles north of the blast, described it as “lurid-colored… curling like long tongues of fire in the sky.” In Isahaya, five miles east of the city, a grandmother feared that “the sun would come falling down,” and a young boy grabbed at ash and paper falling from the sky, only to realize that they were scraps of ration books belonging to residents in the Urakami Valley.

From the top of Mount Tohakkei four miles southeast of Nagasaki, a man loading wood into his truck was “stunned speechless by the beauty of the spectacle” of the giant rising cloud exploding over and over again as it transformed from white to yellow to red. In neighborhoods at the edge of the city, people peered out of windows and stepped outside to see the atomic cloud rising above them, only to bolt back inside or to nearby shelters in anticipation of a second attack.

Inside the city, the bomb’s deadly gale quieted, leaving Nagasaki enveloped in a dark, dust-filled haze. Nearest the hypocenter (the point on the ground above which the bomb exploded), almost everyone was incinerated, and those still alive were burned so badly they could not move. In areas beyond the hypocenter, surviving men, women, and children began extricating themselves from the wreckage and tentatively stood, in utter terror, for their first sight of the missing city. Twenty minutes after the explosion, particles of carbon ash and radioactive residue descended from the atmosphere and condensed into an oily black rain that fell over Nishiyama-machi, a neighborhood about two miles east over the mountains.

Nagano pulled herself up from the floor of the airplane parts factory and stood, quivering, rubbing debris from her eyes and spitting dust and glass fragments from her throat and mouth. Around her, adult and student workers lay cowering on the ground or rose to their feet, stunned and bewildered. Opening her eyes just a bit, Nagano sensed it was too dangerous to stay where she was. She ran outside and squeezed herself into a crowded mountain air raid shelter, where she crouched down and waited for another bomb to drop.

“The whole Urakami district has been destroyed!” one of the male workers called out to her. “Your house may have burned as well!” Nagano fled from the bomb shelter and ran toward the Urakami Valley. Outside, the neighborhood around the factory was almost pitch-dark and hauntingly still. Large trees had snapped in half, tombstones had fallen in a cemetery nearby, and streets were filled with broken roof tiles and glass. Small birds lay on the ground, twitching. Compared to what she had imagined, however, the damages around her seemed minimal, and Nagano — who could not see the Urakami Valley — half believed that her family might be safe after all.

She hurried through the streets to the southern end of Nishiyamamachi toward Nagasaki Station, over a mile to the east, pressing past partially collapsed wooden houses and people fleeing the blast area. As the road curved west, Nagano rushed by the 277-step stone staircase leading up to the seventeenth-century Suwa Shrine, still intact, and Katsuyama Elementary School, just next to City Hall. Forty-five minutes later, Nagano finally passed the mountains that had stood between her and the expanse of atomic destruction.

In front of her, the main building of Nagasaki Station had collapsed. But it was the view to her right that shocked her into finally realizing that the rumors she had heard about the Urakami Valley were true. Where the northern half of Nagasaki had existed only an hour before, a low heavy cloud of smoke and dust hovered over a vast plain of rubble. Nothing remained of the dozens of neighborhoods except tangled electrical wires and an occasional lone chimney. The huge factories that had lined the river near Nagasaki Station were crumpled into masses of steel frames and wooden beams, and the streetcar rails were, in one survivor’s words, “curled up like strands of taffy.”

No trace of roads existed beneath miles of smoking wreckage. Blackened corpses covered the ground. Survivors were stumbling through the ruins moaning in pain, their skin hanging down like tattered cloth. Others raced away, shrieking, “Run! Escape!” A barefoot mother in shredded clothes ran through the wreckage screaming for her child. Most people, however, were silent. Many simply dropped dead where they stood.

Nagano’s house was just over a half mile to the north and west, a 10-minute walk on any other day. She faced in that direction to scan the area, but there was nothing — no buildings, no trees, and no sign of life where she had last seen her mother and younger brother and sister. Her eyes searched frantically for a way home, but the flames spreading through the ruins prevented access from all directions. Paralyzed and confused, Nagano stood in front of Nagasaki Station, alone, with no idea what to do next.

From Nagasaki: Life After Nuclear War by Susan Southard. Reprinted by arrangement with Viking, an imprint of Penguin Random House LLC. Copyright © 2015 by Susan Southard