Atomic bombing of Hiroshima

The Atomic bombing of Hiroshima was the first use of the new weapon against a Japanese city and a decisive turn in the final campaign of the Second World War. For Harry S. Truman, the news arrived not in a formal conference but at lunch with six enlisted men aboard the presidential train at sea. The first reports described the attack as a complete success; the scale of the human consequences was not yet known. The event brought together a secret project, urgent military calculations, and a decision whose immediate promise of ending the war would soon be shadowed by the deaths and suffering in Hiroshima.

A secret weapon and an uncertain choice

Staff investigators had encountered unexplained expenditures for a project identified as Manhattan Project, apparently larger than the Canol Project. In June 1943, Truman telephoned Secretary of War Henry L. Stimson. Stimson told him that only a handful of people knew about the secret development and assured him it served a specific, unique purpose. Truman accepted that assurance without asking for further details. By July, he had learned enough of the project’s essential nature to reassure Lewis Schwellenbach about enormous land condemnations near Hanford, where nearly half a million acres were involved.

Stimson later brought Truman a memorandum describing a weapon that might be ready within four months and could destroy an entire city with a single bomb. The United States and Great Britain had shared in its development, but the United States alone then had the ability to produce it. Stimson also warned that the advantage could not last and that the Soviet Union might be able to enter production within a few years. The disclosure made the project’s scale and international implications explicit; it did not, by itself, settle how the weapon should be used.

The alternatives were considered against the prospect of continued combat. In June 1945, Truman’s diary focused on whether to invade Japan or rely on bombing and blockade; he called the choice his hardest decision to that point. At a White House meeting on June 18, the invasion plan received detailed attention while the atomic bomb was not mentioned. General George C. Marshall described a two-stage operation beginning with Kyushu in November and estimated that the first thirty days could cost about as many casualties as the campaign on Luzon, approximately 31,000. The bomb’s absence from that discussion struck Assistant Secretary of War John J. McCloy as remarkable.

Weighing use and its costs

The advisory committee and its scientific panel considered a technical demonstration against a non-city target, but rejected it. A demonstration might fail to create the shock needed to secure surrender; with probably only one bomb ready, a malfunction or advance warning followed by failure could strengthen Japanese resolve. The panel found no demonstration likely to end the war and no acceptable alternative to direct military use. Marshall had earlier considered a military target followed, if necessary, by attacks on manufacturing centers after warnings, but by this stage his position had changed. The choice was shaped by practical uncertainty as well as by the expectation that a devastating shock might end the fighting.

Stimson told Truman that he did not want the United States to exceed its enemies in atrocities. He was also concerned that conventional raids might leave Japanese targets too devastated to provide a meaningful comparison for the new weapon. Truman reportedly laughed at the juxtaposition, then said he understood. Stimson and Marshall focused on how the bomb might stop the slaughter quickly; Stimson’s earlier instruction to General Groves had been to produce it as soon as possible to bring the war to a conclusion. These arguments did not remove the moral question of attacking a city, but they placed it alongside the anticipated losses of an invasion and the continuing deaths of the war.

At Potsdam, Truman later recalled a consensus among James F. Byrnes, Stimson, Admiral William D. Leahy, Marshall, and General Arnold that the bomb should be used. He said Marshall had emphasized the lives an invasion might cost and recalled Marshall’s estimate of at least a quarter of a million American casualties for a landing on the Tokyo plain and elsewhere in Japan. Truman also wrote that he had reached his conclusion after long and careful thought and did not like the weapon. The account does not identify a single, clear moment when he decided; the momentum of the project and the approaching end of the war made abandoning its use an increasingly unlikely course.

The report reaches Truman

On the morning of August 6, Truman and several members of his party were aboard the presidential train, which had entered the Gulf Stream south of Newfoundland. Shortly before noon, Truman and Byrnes went below deck to eat with the crew. Truman had just begun lunch among six enlisted men when Captain Graham, a Map Room officer, hurried in with a map of Japan and a decoded message from the Secretary of War. The report said Hiroshima had been bombed four hours earlier and that the visible effects exceeded those of any test. Graham had circled the city in red pencil.

Truman reacted with excitement, shook Graham’s hand, and asked him to show the message to Byrnes. A second report soon arrived, placing the bombing at August 5 by Washington time and describing its success as even more conspicuous than the earlier test. Truman then called for the crew’s attention and announced that a new bomb, with more power than twenty thousand tons of TNT, had been dropped on Japan. The men cheered. He repeated the news to officers and described the outcome as a successful gamble. George Elsey later recalled that those present were excited and cheering; within minutes, radio bulletins and the President’s public statement were reaching the ship.

The statement, released by the White House at 11:00 A.M. Washington time, identified the weapon as an atomic bomb and announced that it had been used against Hiroshima. It warned that the United States was prepared to destroy Japan’s remaining capacity to make war and called on Japan to accept the terms offered, threatening further destruction from the air. The statement did not report the extent of damage in Hiroshima: Washington had not yet received those details. For American families with people serving overseas, the announcement brought hope that the war might soon end, but the initial public account foregrounded the weapon’s power rather than the human toll.

Casualties and the changed meaning of success

The first reports from Guam, received on August 8, indicated that 60 percent of Hiroshima had been leveled and suggested that deaths and injuries might reach 200,000. J. Robert Oppenheimer had earlier predicted perhaps 20,000 deaths. Later estimates placed the number killed instantly at about 80,000, with another 50,000 to 60,000 dying over the following months; perhaps 10,000 of the total were Japanese soldiers. Many more people survived with serious burns, shock, or radiation illness. The difference between the early prediction and the later estimates made clear how little was known when Truman first announced the attack aboard ship.

The bomb’s success initially appeared to offer a rapid end to a war whose possible continuation carried enormous costs. Yet the physical results in Hiroshima, and the prospect that other nations would develop the weapon, gave the announcement a second meaning. Leahy warned that the future use of atomic weapons by potential enemies was frightening. Truman, writing to a critic on August 9, said he regretted the necessity of destroying whole populations and would not do so unless absolutely necessary; he also expressed concern for Japanese women and children. That night he urged Japanese civilians to leave industrial cities. The attack therefore stands both as a moment of military decision and as the beginning of a reckoning with the scale and future dangers of atomic power.