Ever since August 6, 1945, when the first atomic bomb detonated over Hiroshima, the human race has lived in fear of nuclear annihilation. In the annals of history, few events have had more import than this first atomic bombing, and no historical figure has been associated with this bomb more than Harry Truman, who commanded his military to use the new weapon less than four months after taking office. In this exclusive adaptation from The Accidental President_—a book covering the first four months of the Truman administration—we observe Truman aboard the USS Augusta, on his way home from the Potsdam Conference in Soviet-occupied Germany as the bombers gunned for Hiroshima and after, when the President learned that the Manhattan Project was, in his words, “a terrible success.”_

The first night at sea, Truman’s party gathered at 8:30 p.m. in Secretary of State James F. Byrnes’s cabin for a movie—Wonder Man, about a nightclub owner who gets murdered by gangsters and comes back as a ghost to haunt his killers. Truman skipped the film and stayed in his cabin. One can imagine him staring at the ceiling, exhausted and tense from the anticipation of an explosion that would soon change the world.

He had told himself in his diary, days earlier, that “military objectives and soldiers and sailors are the target and not women and children.” Surely he knew that this bomb, as technologically marvelous as it was, did not have the sentience to separate military individuals from civilians. He could only hope that it would serve its purpose: to end the war, to save lives.

In the Far East, Japan continued to burn, the result of the U.S. Army’s B-29 firebombing raids of cities such as Mito, Fukuyama and Otsu. On August 2, the day Truman started his transatlantic journey home aboard the Augusta, Major General Curtis LeMay’s 21st Bomber Command struck the enemy with what The New York Times called “the greatest single aerial strike in world history.” Nearly 900 B-29s pounded targets with 6,632 tons of conventional and incendiary bombs. The flames engulfed miles of Japanese cities. These attacking planes saw no opposition.

As the Augusta pushed deeper into the Atlantic, Truman’s curiosity over the bomb grew excruciating. Given the secrecy of the mission, he received no updates. At one point, the Augusta’s Advance Map Room cabled the White House inquiring about any news of “the Manhattan Project.” White House Map Room operatives responded that they could find no evidence of any such project.

From his headquarters on Guam in the South Pacific, at 2 p.m. on August 5, General LeMay, who had overseen the recent firebombing of Japan’s important industrial cities, gave the final go-ahead for the 509th wing to fly the secret mission the following day—August 6.

Only recently had LeMay learned of the bomb. A special messenger had flown to his headquarters on Guam to brief him. “I didn’t know much about this whole thing and didn’t ask about it, because it was so hot,” LeMay recorded. “Didn’t wish to have any more information than it was necessary for me to have.” He had orders as to the first bomb’s primary target: Hiroshima. According to intelligence sources, Hiroshima was “an Army city . . . a major quartermaster depot” with warehouses full of military supplies. Intelligence sources also found that Hiroshima had no POW camps, so the Americans could be relatively sure they would not be bombing their own men.

LeMay’s command had not yet hit Hiroshima. It was a thriving city and a virgin target, with a population of 318,000, according to American intelligence.

On the afternoon of August 5, on the island of Tinian, army officials pushed the Little Boy bomb out of a warehouse at the airfield. A dozen men in short-sleeved tan uniforms gathered around it wearing expressions of concern, wheeling Little Boy on a platform as if it were a patient on a hospital gurney. It was roughly egg-shaped, with a steel shell and a tail poking out the back to guide its trajectory. One of the men working at Tinian that day described it as looking like “an elongated trash can with fins.” When it came to the Manhattan Project, everything was experimental. Little Boy employed a different gun mechanism than the one used in the Trinity atomic test, which had successfully gone off in New Mexico roughly two weeks earlier, so there was no certainty that this weapon would work.

The Tinian airbase was itself an industrial marvel, an emblem of American ingenuity. A year earlier, most of this little island was covered in sugarcane. Now it was home to the largest airfield on earth. The airport had been built to serve one purpose above all others: Little Boy. On the afternoon of August 5, army personnel eased the weapon through open bomb-bay doors into the belly of a B-29 Superfortress, using a hydraulic lift.

That very afternoon the pilot of this B-29, Paul W. Tibbets, had named the airplane Enola Gay, after his mother. Surely Mrs. Tibbets had never dreamed that her legacy would carry such historical import, for the Enola Gay was about to become the most infamous military aircraft ever known. It would fly as part of a seven-plane task force—all B-29s—including three for weather recon, one carrying blast-measurement equipment, one for camera equipment and observation, one spare aircraft and the delivery plane itself, the Enola Gay.

The final briefing for the seven flight crews was at midnight. Less than 48 hours earlier, they had learned of the atomic bomb for the first time, the secret behind the mission for which they had been training for months. They were shown aerial photographs of the targets—the primary, Hiroshima, and secondaries, Kokura and Nagasaki. They were told details of the Trinity shot; and while they were supposed to see footage of Trinity, the motion-picture machine had broken, so the bomb’s visual effects remained a mystery to them. They had known they were training for something special, but still, they were amazed. “It is like some weird dream,” said one crew member, radioman Abe Spitzer of Wendover, Utah, “conceived by one with too vivid an imagination.”

During the final briefing, crew members were given dark glasses to protect their eyes from the blast, which, they were told, would be like a new sun being born. A weatherman briefed them on what to expect—smooth flying—then a chaplain gave a blessing, asking the Almighty Father “to be with those who brave the heights of Thy heaven and who carry the battle to our enemies.”

Thousands of miles away aboard the Augusta, at nearly this exact moment, Truman was attending his own church services in the ship’s forward mess hall, for it was still August 5, a Sunday. With Secretary of State Byrnes and the Augusta’s skipper, Captain James Foskett, by his side, Truman prayed as the ship’s chaplain led the group in a hymn: “Faith of our fathers, we will strive/To win all nations unto Thee/And through the truth that comes from God/Mankind shall then indeed be free.”

At 2:27 a.m. on Tinian, Tibbets sparked the Enola Gay’s four Wright Cyclone engines, and the plane pushed forward onto a runway. It had been given the code name Dimples 82. Tibbets called to flight control. The quick conversation as he later remembered it: “Dimples Eight Two to North Tinian Tower. Taxi-out and take-off instructions.”

Orders returned: “Dimples Eight Two from North Tinian Tower. Take off to the east on Runway A for Able.”

The co-pilot, Robert Lewis, counted down: “Fifteen seconds to go. Ten seconds. Five seconds. Get ready.”

At 2:45 a.m., the Enola Gay’s wheels left the ground.

By the time Truman sat down to dinner at 6 p.m. on August 5, the Enola Gay was rendezvousing with two escorts over the island of Iwo Jima at 9,300 feet. In the South Pacific, the sun was just rising on August 6. At 7:30 a.m., William Sterling Parsons—the ordnance expert who had worked on the bomb at Los Alamos, and who was now aboard the Enola Gay as the weaponeer—climbed down to the bomb bay and armed Little Boy, pulling out green plugs and replacing them with red ones. Weather was clear, so Tibbets decided to gun for the primary target. “It’s Hiroshima,” he announced over the intercom, throttling the Enola Gay upward to 31,000 feet. The crew slipped on heavy flak suits, and Tibbets reminded them to don their heavy glasses at the moment of detonation.

At 8 p.m. on August 5 aboard the Augusta, the evening’s film presentation began—The Thin Man Goes Home, starring William Powell and Myrna Loy. Again, Truman did not attend. He might have been playing poker, or staring at the ceiling of his cabin, or perhaps still praying, alone.

Around the time the film began, Little Boy’s target came into focus. “I see it!” yelled the Enola Gay’s bombardier, Thomas Ferebee. The airplane was traveling at 328 miles per hour on automatic pilot at 31,000 feet when Ferebee took aim in his bombsight. Hiroshima lay below. Copilot Robert Lewis was taking notes in a logbook during the mission. Looking down at Hiroshima, he wrote the words “perfectly open target.” Ferebee let the bomb loose. “For the next minute,” Lewis wrote, “no one knew what to expect.”

Tibbets recalled: “I threw off the automatic pilot and hauled Enola Gay into the turn. I pulled antiglare goggles over my eyes. I couldn’t see through them; I was blind. I threw them to the floor. A bright light filled the plane. The first shock wave hit us.”

Copilot Lewis recorded: “There were two very distinct slaps on the ship, then that was all the physical effects we felt. We then turned the ship so we could observe the results and then in front of our eyes was without a doubt the greatest explosion man has ever witnessed . . . I am certain the entire crew felt this experience was more than any one human had ever thought possible . . . Just how many Japs did we kill? . . . If I live a hundred years I’ll never quite get these few minutes out of my mind.”

In the moment, Lewis was writing in his logbook, scribbling with difficulty since it was dark in the vibrating aircraft. He wrote, “My God, what have we done?” Tibbets recalled: “We turned back to look at Hiroshima. The city was hidden by that awful cloud . . . boiling up, mushrooming, terrible and incredibly tall. No one spoke for a moment; then everyone was talking. I remember Lewis pounding my shoulder, saying ‘Look at that! Look at that! Look at that!’ Tom Ferebee wondered about whether radioactivity would make us all sterile. Lewis said he could taste atomic fission. He said it tasted like lead.”

On the ground, it was 8:15 in the morning. The city was bustling, as 45 minutes earlier, citizens received an “all clear” message, that it was safe to go outside. When the bomb detonated, many thousands of citizens of Hiroshima disappeared off the face of the earth, instantly and without a trace. Survivors would remember the flash of light first, followed by a sound that had never been heard by human ears. “We heard a big noise like a ‘BOONG!’ ‘BOONG!’ Like that. That was the sound,” Tomiko Morimoto, who was 13 at the time, later recalled. And then, “everything started falling down; all the buildings started flying around all over the place. Then something wet started coming down, like rain. I guess that’s what they call black rain. In my child’s mind, I thought it was oil. I thought the Americans were going to burn us to death. And we kept running. And fire was coming out right behind us.”

Only one person reported to be within a 100-yard radius of Hiroshima’s ground zero survived the blast. His name was Goichi Oshima. Ten years later he described what he saw: “A sudden flash, an explosion that defies description, then everything went black. When I came to, the Hiroshima I knew was in ruins.”

Aboard the Augusta, Truman went to bed that night likely within an hour or two after detonation. At 1 a.m. (now August 6), the ship crossed into a new time zone in the Atlantic and the officers set clocks back one hour. Truman awoke to a beautiful quiet day at sea, the sun bright and warm. The ship’s officers shifted to warm-weather uniforms: khaki and gray, with the crew in white, due to the Gulf Stream’s temperate breezes. After breakfast, Truman relaxed on the deck and listened to the ship’s band play a concert, unaware at this moment that Hiroshima had been all but wiped off the planet.

Truman, tense with excitement, shares the news.

As Truman took lunch aboard the Augusta, Frank Graham, a navy captain working in the Advance Map Room, hurried into the mess hall minutes before noon—some 16 hours after the destruction of Hiroshima—and handed Truman a message:

“Hiroshima bombed visually with only one-tenth cover at 052315A. There was no fighter opposition and no flak. Parsons reports 15 minutes after drop as follows: ‘Results clear cut and successful in all respects. Visible effects greater than in any test. Conditions normal in airplane following delivery.’ ”

Truman jumped to his feet and shook hands with the messenger. “Captain,” the President said, “this is the greatest thing in history! Show it to the Secretary of State.” Graham handed the message to Byrnes, who read it and belted out the words “Fine! Fine!”

Minutes later Graham returned with another message, this one from Secretary of War Henry Stimson in Washington. Truman read:

“From the Secretary of War: Big bomb dropped on Hiroshima August 5 at 7:15 p.m. Washington time. First reports indicate complete success which was even more conspicuous than earlier test.”

Holding the two messages in his hand, Truman turned to Byrnes and shouted, “It’s time for us to get on home!” Then he signaled to the mess-hall crowd to quiet down, banging a piece of silverware against a glass. The sailors hushed, and Truman announced the news. The room exploded in applause, feeding off the president’s excitement. With Byrnes at his heels, Truman marched quickly to the wardroom, where the Augusta’s officers were lunching. In a voice “tense with excitement,” according to one man present, Truman said, “We have just dropped a bomb on Japan which has more power than 20,000 tons of TNT. It was an overwhelming success.”

All over the Augusta, the mood soared among sailors. It could be summed up in a sentence spoken by one of them that afternoon: “I guess I’ll go home sooner now.”

In Washington, assistant press secretary Eben Ayers gathered reporters working their usual White House beat. Ayers had been briefed about the bomb a few days earlier and warned to keep it top secret until further orders. Now it was go time. Press secretary Charlie Ross had cabled from the Augusta that it was time to release the president’s statement. Ayers called out to the newsmen.

“I have got here what I think is a darned good story. It’s a statement by the president, which starts off this way.” Ayers read aloud the first paragraph: “ ‘Sixteen hours ago an American airplane dropped one bomb on Hiroshima, an important Japanese Army base. That bomb had more power than 20,000 tons of TNT. It had more than two thousand times the blast power of the British ‘Grand Slam,’ which is the largest bomb ever yet used in the history of warfare.’ ”

Ayers continued in his own words: “It is an atomic bomb, releasing atomic energy. This is the first time it has ever been done.”

One reporter yelled out: “It’s a hell of a story!”

Aboard the Augusta, and in millions of households, Americans gathered around their radios, listening to Truman’s statement being read over the airwaves. His statement spoke of “a harnessing of the basic power of the universe . . . We are now prepared to obliterate more rapidly and completely every productive enterprise the Japanese have above ground in any city. We shall destroy their docks, their factories and their communications. Let there be no mistake; we shall completely destroy Japan’s power to make war . . . If they do not now accept our terms, they may expect a rain of ruin from the air, the likes of which has never been seen on this earth.”

Truman held a press conference on the ship, reading his statement again and answering questions about the greatest wartime secret of all. He read his statement for newsreel cameras also, speaking soberly into the camera: “The Japanese began the war from the air at Pearl Harbor. They have been repaid manyfold.”

Immediately, American and British news sources began monitoring Japanese radio, where already, cryptic announcements were being made—rail service in and around Hiroshima had been canceled, and the scene in that city was under investigation.

That afternoon a curious scene unfolded aboard the Augusta. At 3:30, less than four hours after the president received word of Little Boy, Truman and members of his party sat watching a boxing program on the ship’s deck, with the Gulf Stream’s warm breezes swirling their hair. Surely the words of his atomic-bomb statement were still echoing in his head. He understood that the bomb had ushered in not just a new era of humanity’s understanding of nature’s forces, but also a new understanding of humanity’s capacity for self-destruction. Maybe the bomb would win the war. But at what cost?

“I shall give further consideration,” Truman’s statement had ended, “and make further recommendations to the Congress as to how atomic power can become a powerful and forceful influence towards the maintenance of world peace.”

A.J. Baime is the author of THE ACCIDENTAL PRESIDENT: Harry S. Truman and the Four Months that Changed the World.