"Dimples Eight Two" weighed 150,000 pounds, and with fuel for the long flight to Hiroshima, 12 men on board, and a five-ton uranium bomb in the bay, the B-29 was 15,000 pounds overweight.
The pilot, Col. Paul W. Tibbets Jr., 30, had handpicked the airplane on the assembly line in Nebraska three months before and had just had his mother's name, "Enola Gay," painted in black letters on the nose.
As the plane rumbled down the airstrip at over 100 mph, he had his lucky cigarette case with him in one pocket, and a box containing 12 cyanide capsules in another.
On Aug. 6, 1945, 75 years ago today, no one was sure how Special Bombing Mission No. 13, the world's first atomic attack, would go.
Would it end in disaster for the crew in Japan? Eight downed American airmen had been beheaded by the Japanese a few weeks before. Would it end in the obliteration of Hiroshima? Would the overweight airplane with the crazy call sign even get off the runway? Would the crew have need for the cyanide?
Two other B-29s, the "Great Artiste" and "Necessary Evil," were supposed to go along to take pictures and record data.
But "Enola Gay" was the "strike ship."
Fifteen hundred miles to the north-northwest, under a waning crescent moon, lay a 400-year-old Japanese city most Americans probably had never heard of but whose name was about to be etched into the pages of history.
It was an important enemy military site with a wartime population about 280,000, according to the historians Gordon Thomas and Max Morgan-Witts.
Almost half of them were about to be incinerated, crushed, and irradiated by the crude atomic weapon named "Little Boy" that the Enola Gay carried.
Tens of thousands more would die the same way at Nagasaki a few days later, and the world would subsequently be hearing about megatons, mutual assured destruction, proliferation, nuclear winter, meltdowns and dirty bombs.
It would be the start of a frightful era of weapons that could defy control and menace civilization.
But as "Dimples Eight Two" picked up speed that morning, its mission was born of its time: deliver a blow that the United States hoped might finally end the global butchery of World War II. (The war in Europe had ended in May.)
This week, commemorations are scheduled across the country, with socially distanced candlelight vigils and the tolling of bells, and because of the covid-19, ceremonies and remembrances have moved online.
More than 100,000 American soldiers, sailors and Marines had already been killed in the Pacific since Japan's attack on the U.S. naval base at Pearl Harbor on Dec. 7, 1941. At the time of the Hiroshima bombing, average of 5,000 were still dying each week.
The fighting on land, at sea and in the air had been savage. Naval and air battles had been sudden, brief and deadly. Huge ships went to the bottom with their crews. Japanese suicide pilots crashed their planes into American vessels. One air battle was so lopsided in favor of the Americans that it was called a turkey shoot.
The fighting on land was different. Battles went on for months and were often fought hand-to-hand, with rifles, knives and flame throwers. Grim engagements at places like Guadalcanal, Tarawa, and Iwo Jima became legendary.
The most recent, the battle for the Japanese island of Okinawa, had ended six weeks earlier, after two months and the deaths of 12,000 Americans and 100,000 Japanese.
And American units were already training for a massive invasion of the Japanese home islands of Kyushu and Honshu - in Operation Olympic, set for November 1945, and Operation Coronet, planned for March 1946, according to the historians Norman Polmar and Thomas B. Allen.
Landing beaches had been designated, and named after cars and car parts - Cadillac, Chevrolet, Gearshift and others. More than a million men would be involved.
The Japanese were expected to resist ferociously, and American casualties would be enormous. President Harry S. Truman feared "an Okinawa, from one end of Japan to the other."
Tibbets' task was to try to prevent that. If this frightening new weapon worked, the thinking went, it would shorten the war, albeit at a dreadful cost in human life.
But first the Enola Gay had to get off the ground.
The lumbering aluminum plane with a 141-foot wingspan had been stripped of its armor and all defensive weaponry but its tail guns. But it still weighed 65 tons by itself and carried 7,000 gallons of fuel.
As the plane strained to gain speed, Tibbets knew he was using up a lot of runway. Four B-29s had crashed and exploded on Tinian the night before, according to historians.
"If we crack up and the plane catches fire, there is danger of an atomic explosion that could wipe out half this island," said Navy Capt. William Parsons, who flew on the mission as the bomb specialist.
And because of that risk, the 10-foot-long "Little Boy" had not yet been armed.
It was a "gun-type" bomb, one in which an explosive charge would fire a "subcritical" piece of uranium 235 down a six-foot-long "gun" barrel into a second subcritical piece of uranium, according to Thomas and Morgan-Witts.
This created critical mass and the explosive nuclear chain reaction that would lay waste to Hiroshima.
The four cloth bags of explosive and the detonator would not be inserted until the plane was in the air.
The Enola Gay was now doing 180 mph but was running out of ground.
Sitting beside Tibbets, the co-pilot, Capt. Robert Lewis, was alarmed.
"She's too heavy!" he shouted. "Pull her off - now!"
When Tibbets, who was known as "Old Bull," did not respond, Lewis reached for the duplicate steering yoke in front of him, according to Thomas and Morgan-Witts.
"No!" Tibbets said. "Leave it!"
Another crewman yelled, "Hey, aren't we going to run out of runway?"
At the last second, Tibbets lifted the bomber's nose and "Dimples Eight Two" was streaking over the dark ocean on its way to Hiroshima.
The hour was early; the morning still, warm, and beautiful. Shimmering leaves, reflecting sunlight from a cloudless sky, made a pleasant contrast with shadows in my garden . . . - Michihiko Hachiya.
About 6 a.m. in Hiroshima, the air raid siren went off and blared for a full minute. It was the third alert of the day. People didn't panic at the sound, because the siren went off routinely every morning at this time when an American weather plane passed.
Hiroshima was sprawled across the flat delta formed by the multiple channels of the Ota River, which flows out of the highlands to the north and west and empties into Hiroshima Bay in southern Japan.
The city, whose name means "broad island," was built on a scattering of islands and had 82 major bridges.
It was a city of mostly wooden houses, with bustling shopping districts lined with stalls. There was a Methodist cathedral, trolley lines, an airport and streets crowded with bicycles, horse carts and cars. It had a modern domed Industrial Promotion Hall, a 350-year-old pagoda-style castle, and a Red Cross hospital.
Japan had been at war for 14 years in China and other Asian countries, and for 3Â½ years with the United States and the Allies. Many people were hungry and ragged.
In the previous 10 months, the Americans had dropped 157,000 tons of bombs on Japan, the military historian Richard B. Frank wrote in his 1999 book, "Downfall."
In Tokyo, 97,000 people had been killed and 700,000 dwellings had been destroyed. In Osaka, 9,000 people had been killed. In Nagoya, 8,000 had perished. The bombings had killed 6,000 in Kobe and 4,000 in Yokohama.
Hiroshima, even though it was a regional army headquarters with 40,000 men, the site of large supply depots and a major military embarkation port, had been spared the attentions of "Mr. B" or "B-San" as the Japanese called the B-29s.
Some thought there were reasons that the bombers hadn't come: Citizens of Hiroshima had relatives in the United States; the city was too beautiful, and Americans wanted to build villas there after the war; President Truman's mother lived nearby; the city wasn't on American maps.
Two days before, 720,000 leaflets had been dropped warning that Japanese cities would be destroyed if Japan did not surrender. "Bombs have no eyes," the leaflets said, urging residents to evacuate. Tens of thousands already had.
That morning, people were going about their early chores, the psychiatrist and author Robert Jay Lifton wrote in his book "Death in Life, Survivors of Hiroshima." Workers headed to factories. People read the morning paper, Chugoku Shimbun. Many were out in the open.
The all-clear sounded about 7:30 a.m.
"The sky was serene, the air was flooded with glittering morning light," a history professor remembered. "I was in a state of absent-mindedness. The sirens and also the radio had just given the all-clear signal. I had reached the foot of the bridge where I halted."
Thirty-one thousand feet above, the Enola Gay's bombardier, Maj. Thomas Ferebee, 26, peered through the Norden bomb sight under the plane's greenhouse-like canopy in the nose.
He was looking for the unique structure of the T-shaped Aioi Bridge, which was the aiming point for the drop. (The Japanese air raid system had just picked up the new intruders, but its warning would come too late.)
About an hour earlier, after the bomb had been fully armed, Tibbets had revealed to the crew over the intercom that they were carrying the world's first atomic weapon.
Now, flying at 200 mph, they were almost over the target. Most of the crew put on dark welder's glasses.
"I've got it!" Ferebee called when he spotted the bridge.
Fifteen seconds passed.
At 8:15 and 17 seconds, the doors of the bomb bay opened.
"Bomb away!" Ferebee yelled.
"Little Boy" tumbled out tail first, flipped over nose down, and began to fall through the last 43 seconds of the old era.
The bomb was designed to explode over the city at an altitude of about 1,900 feet. So it had an internal radar system that detected the ground, tripped the detonator at that altitude, and initiated the detonation sequence.
The bomb traveled for six miles and exploded just short of the bridge.
The Enola Gay, meanwhile, lurched upward on shedding the weight of the bomb and executed a hairpin turn to escape the expected shock wave of the blast.
At first, the crew saw and felt nothing. Then a giant slow-motion column of smoke and fire rose from the ground and blossomed.
Tail gunner George R. Caron, 25, who had with him his Brooklyn Dodgers baseball cap and a picture of his wife and infant daughter for good luck, could see the shock wave coming fast. He yelled, just as the wave slammed into the plane. Another one hit and passed.
Tibbets asked the men over the intercom what they could see so it could be recorded for posterity.
"A column of smoke rising fast [with] a fiery red core," Caron said, according to the historians Thomas and Morgan-Witts. "A bubbling mass, purple-gray in color . . . like a mass of bubbling molasses. The mushroom is spreading out. It's maybe a mile or two wide and half a mile high."
"The city must be below that," he said.
In Hiroshima, Michihiko Hachiya, a physician, had gotten home after a sleepless night as an air warden in his 125-bed government hospital. Clad in his underwear, he was resting on the living room floor.
Suddenly there was a brilliant flash of light that illuminated a stone lantern in his garden. He wondered whether it was sparks from a passing trolley.
Elsewhere, the Hiroshima history professor remembered that "a blinding . . . flash cut sharply across the sky . . .[followed by] dead silence . . . probably a few seconds . . . and then a . . . huge 'boom' . . . like the rumbling of distant thunder."
"At the same time a violent rush of air pressed down my entire body," he recalled. "I raised my head, facing the center of Hiroshima to the west . . .[and saw] an enormous mass of clouds . . .[that] spread and climbed rapidly . . . into the sky.
"Then its summit broke open and hung over horizontally," he remembered. "It took on the shape of . . . a monstrous mushroom [with] with the . . . tail of a tornado. Beneath it more and more boiling clouds erupted and unfolded sideways . . . continuously changing."
At Ground Zero, the bomb generated a hot core of about 7,000 degrees Fahrenheit. People nearby were turned to ash. One dead man was seen still on his bicycle, leaning against a bridge railing. Many had their faces and ears melted off. The odor of burned hair was in the air.
The rivers began to fill with corpses.
The blast blew away houses as if in a toy town. Many victims had their clothes and eyeglasses stripped off and found themselves suddenly naked.
Shadows cast by humans were burned onto buildings. Kimono patterns were burned onto skin. Skin was burned loose and fell away. About 80,000 people were killed immediately, and the toll quickly grew to at least twice that.
Windy firestorms developed, and an eerie black rain fell.
Hachiya's house collapsed. His clothes had been torn off. He called for his wife, and, stunned and bleeding, they made their way outside.
"The shortest path to the street lay through the house next door," he recalled in his 1955 memoir, "Hiroshima Diary." "We went - running, stumbling, falling . . . until in headlong flight we tripped over something and fell sprawling into the street."
"Getting to my feet, I discovered that I had tripped over a man's head," he wrote. "'Excuse me! Excuse me, please!' I cried hysterically . . . The head had belonged to a young officer whose body was crushed beneath a massive gate."
The couple staggered toward the hospital. He was covered only with his wife's apron. He remembered moving in silence through a fog of smoke and dust.
"There were the shadowy forms of people . . . like walking ghosts," he wrote. "Others moved . . . like scarecrows, their arms held out from their bodies with forearms and hands dangling . . . I suddenly realized that they had been burned and were holding their arms out to prevent the painful friction."
"A naked woman carrying a naked baby came into view," he remembered. "I averted my gaze. . . . But then I saw a naked man, and it occurred to me that, like myself, some strange thing had deprived them of their clothes."
"No one spoke," he recalled. "Why was everyone so quiet?"
The hospital was on fire.
"The streets were deserted except for the dead," he wrote. "Some looked as if they had been frozen by death while in the full action of flight; others lay sprawled as though some giant had flung them . . . from a great height."
Another doctor had watched the sad parade of the injured pass his house trying to get out of town.
"The sight of them was almost unbearable," he told Hachiya. "Their faces and hands were burnt and swollen; and great sheets of skin had peeled away from their tissues to hang down like rags."
"They moved like a line of ants," he said. "This morning . . . I found them lying on both sides of the road so thick that it was impossible to pass without stepping on them."
The devastation was almost total. "Hiroshima was no longer a city," Hachiya recalled.
As the Enola Gay and its two escort planes headed back Tinian, a young scientist named Luis W. Alvarez, who would later win the Nobel Prize in physics, sat aboard the "Great Artiste" flying at 28,000 feet and wrote a letter to his 4-year-old son.
Alvarez had been worried that all the kinks in the bomb had not been worked out. But over Hiroshima, as he had watched from a port hole in the plane, he had seen the flash - "many times brighter than the sun" - and knew that all had gone as planned.
"Dear Walter," Alvarez wrote:
"This is the first grown-up letter I have ever written to you, and it is really for you to read when you are older. During the last few hours I have been thinking of you and your mother and our little sister Jean. It was tough to take off on this flight, not knowing whether I would ever see any of you again . . ."
The story of our mission will probably be well known to everyone by the time you read this, but at the moment only the crews of our three B-29s, and the unfortunate residents of the Hiroshima district in Japan are aware of what has happened . . .
"What regrets I have about being a party to killing and maiming thousands of Japanese civilians this morning are tempered with the hope that this terrible weapon we have created may bring the countries of the world together and prevent further wars . . ."
"We are . . . on the home stretch [now], so I'll stop writing . . . I wanted to tell you about this while it was still fresh in my mind.
"With much love from