The Hiroshima atomic detonation on August 6, 1945, made the new weapon a reality not as an experiment in the New Mexico desert but over a city. The book follows the event through the chain of people who prepared, delivered, reported, and then tried to understand it: J. Robert Oppenheimer, who had organized the bomb’s development and specified how it should be dropped; John Manley, sent to Washington to report the result; and scientists and servicemen whose first reactions ranged from relief and exhilaration to horror. The bombing’s significance lies not only in its destructive power, but in the abrupt collision between the project’s technical success and the human consequences that success had set in motion.

Targeting and the final instructions

In the weeks after the Trinity test, Oppenheimer knew the weapon had become a military instrument and that Japanese cities were being considered as targets. Anne Wilson, his secretary, recalled that officers were selecting targets and that Oppenheimer grew still and ruminative as he contemplated what was coming. On a walk with Wilson, he puffed on his pipe and said, “Those poor little people, those poor little people.” The remark registered distress, but it did not mean he withdrew from the work of making the attack effective.

On the evening of July 23, Oppenheimer met General Thomas Farrell and Lieutenant Colonel John F. Moynahan, the officers assigned to supervise the bombing run from Tinian. Pacing and chain-smoking, he insisted that the bomb be dropped visually: the crew must see the target, avoid clouds, rain, and fog, and not rely on radar to make the drop. Radar could be used to check the release, he said, but not to replace visual aiming. He also warned against detonating the weapon too high, because that would reduce the damage to the target. The instructions were specific and operational, not abstract: Oppenheimer was anxious that the weapon he had helped bring into existence be delivered as intended.

The bombardiers followed his instruction and dropped the bomb visually on the center of Hiroshima. The later account distinguishes this from the attack on Nagasaki, where cloud cover and dwindling fuel meant the bomb was delivered largely by radar. That contrast gives the Hiroshima mission a particular place in the account: the weapon’s first use was carried out according to the precise visual targeting procedure Oppenheimer had pressed upon the officers.

The detonation and delayed report

At 8:14 a.m. on August 6, the B-29 Enola Gay, named for its pilot Paul Tibbets’s mother, dropped the untested gun-type uranium bomb over Hiroshima. In Washington, John Manley waited for the report. Oppenheimer had sent him there specifically to convey news of the bombing to Los Alamos. After a five-hour communications delay, Manley received a teletype from Captain Parsons, the aircraft’s arming officer, reporting that “the visible effects were greater than the New Mexico test.”

Before Manley could call Oppenheimer, Leslie Groves stopped him. Information about the bombing was not to be released until the president made his announcement. Frustrated, Manley went for a midnight walk in Lafayette Park, across from the White House. The next morning, he learned that President Harry S. Truman would speak at 11:00. Manley finally reached Oppenheimer just as Truman’s statement was released over nationwide radio. Although the two men had agreed on a code for conveying the news, Oppenheimer opened with the exasperated question, “Why the hell did you think I sent you to Washington in the first place?” The delay and the restriction on communication turned a carefully arranged reporting assignment into an encounter with the government’s control of the news.

At 2:00 p.m. that day, Groves called Oppenheimer to congratulate him and the Los Alamos team. Oppenheimer replied, “I have my doubts, General Groves.” Groves answered that he had never shared those doubts. Their exchange placed two interpretations of the same result side by side: for Groves, the successful delivery warranted congratulations; for Oppenheimer, success was already shadowed by reservations.

Celebration, unease, and the human cost

When the news reached Los Alamos over the public-address system, Frank Oppenheimer was standing in the hallway outside his brother’s office. His first thought was, “Thank God, it wasn’t a dud.” Within seconds, however, he recalled, “One suddenly got this horror of all the people that had been killed.” That quick reversal—from relief that the weapon worked to awareness of those killed—echoed the more divided response among the people who had built it.

The announcement brought crowds into hallways in search of radios. That evening, a young physicist remembered an auditorium audience cheering and stamping its feet as Oppenheimer entered up the central aisle rather than from the wings. Onstage, he clasped his hands and raised them over his head like a prizefighter. He told the crowd it was too early to know the results, but that he was sure the Japanese did not like it; he said he was proud of what the group had accomplished. According to the same account, the audience roared when he regretted that the bomb had not been developed in time to use against Germany. The moment presented Oppenheimer in the triumphant role his audience expected, although the book stresses how poorly that role fitted the doubts expressed elsewhere.

Celebration was not the only response. Phil Morrison, who had helped prepare the bomb on Tinian, recalled attending a party and then sitting on the edge of a cot wondering what was happening on the other side, in Hiroshima. Accounts differ over whether scientists at Los Alamos celebrated the bombing: Alice Kimball Smith said that “certainly no one” celebrated, while also describing an attempted party that became a “memorable fiasco.” Servicemen reported parties and dancing. Oppenheimer attended one gathering, but on leaving saw a physicist retching in the bushes. The sight made him realize that an accounting had begun. The scene does not resolve the conflicting reports into a single communal reaction; it shows how celebration and distress occupied the same place and the same evening.

Witness, memory, and the bomb’s meaning

The physical evidence became more immediate when Morrison and Robert Serber returned from Hiroshima and Nagasaki in October with the first group of scientific observers. Morrison had reached Hiroshima thirty-one days after the bombing. He reported that people in the streets for nearly a mile had been seriously burned by the heat; some suffered burns in the pattern of their striped clothing. Others escaped damaged homes with apparently slight injuries, only to die days or weeks later from radiation exposure. In a radio account, he described the city as scorched and leveled, and emphasized the scale of destruction achieved by a single bomber and a single bomb against a city of three hundred thousand. The report gave the event a human and physical aftermath that the initial news of a successful military operation could not convey.

In Nagasaki, Serber noticed telephone poles charred on the sides facing the explosion, following them for more than two miles from ground zero. He also saw a horse whose hair had been burned off on one side while the other remained normal. When Serber remarked that the horse seemed to be grazing happily, Oppenheimer scolded him for creating the impression that the bomb was benevolent. His rebuke makes explicit the difficulty of treating visible details as evidence of a harmless or contained weapon: even an apparently ordinary image could mislead if detached from the violence that produced it.

Oppenheimer later recalled the Trinity test through a passage from the Bhagavad Gita, saying that the sight of the cloud had made clear that the world would not be the same. In a 1965 television documentary about the decision to use the bomb, he again recited, “Now I am become death, the destroyer of worlds.” The recollection concerns Trinity rather than the Hiroshima detonation, but its later public circulation joined the two events in memory: the test that demonstrated the weapon and the bombing that used it. The account also records the gap between that solemn image and the public performance at Los Alamos, where Oppenheimer had appeared to lead a celebration.

The bombing also informed Oppenheimer’s later arguments about nuclear policy. In 1949, as the General Advisory Committee considered a proposed thermonuclear weapon, he and the majority warned that a weapon far more powerful than the Hiroshima bomb could become a weapon of genocide, and that possessing it could damage American security as well as world opinion. The committee’s report argued that existing atomic bombs could provide effective retaliation even if the Soviet Union developed a super bomb, and favored more limited forces over an escalating accumulation of weapons. The Hiroshima detonation thus remained more than the proof that a device could be delivered and explode: it was a benchmark against which Oppenheimer and other scientists assessed the expanding destructive scale of subsequent weapons, and a lasting source of tension between military success and moral consequence.