Decision to Use Atomic Bombs Against Japan

The Decision to Use Atomic Bombs Against Japan was a consequential wartime choice made under pressure to end the fighting and uncertainty about the costs of the alternatives. Its course was shaped by a civilian committee’s recommendation, the prospect of an invasion of Japan, and Harry S. Truman’s conviction that the bomb should be used to save American lives. Yet the account does not reduce the decision to a single instant: Truman’s later recollections describe deliberation and reluctant agreement, while the sequence of events suggests that the project’s momentum left little realistic room to reverse course.

A secret project and a civilian decision

For much of the war, the scale and purpose of the Manhattan Project were concealed even from Truman. In June 1943, while still a senator, he called Secretary of War Stimson after staff investigators encountered unexplained expenditures associated with the project. Stimson told him it was a highly important secret development and that only a handful of people knew about it. Truman accepted that assurance and did not press him for details. By July, however, Truman had learned enough to reassure Lewis Schwellenbach about vast land condemnations near Hanford, Washington, involving nearly half a million acres.

As President, Truman received a stark account of the weapon’s likely power. Alone with Stimson in his office, he read a memorandum warning that within four months the United States would probably have completed a weapon capable of destroying a whole city. The United States and Britain had shared in its development, but only the United States could then produce it; Stimson also warned that the Soviet Union might be able to do so within a few years. The bomb therefore presented not only an immediate question about Japan, but a looming problem of international power.

The Interim Committee on S-1 was organized as a secret, entirely civilian body chaired by Stimson. Its members included senior government officials and scientists, with James Byrnes serving as Truman’s personal representative. The committee’s first meeting took place at the Pentagon on May 9, 1945. It reconvened on May 14 and May 18, then held a crucial two-day session beginning May 31 with an advisory panel of physicists, including J. Robert Oppenheimer, director of the Los Alamos Laboratory. Stimson framed the stakes as a responsibility to recommend action that might turn the course of civilization.

The recommendation and the alternatives

The committee considered the Soviet Union as well as Japan. General Marshall raised the possibility of inviting Soviet scientists to witness the first test. Byrnes objected, favoring rapid progress in production and research to keep the United States ahead while seeking better political relations with Russia. After discussion, the committee and scientific panel reached three unanimous conclusions: the bomb should be used against Japan as soon as possible; it should be directed at war plants surrounded by workers’ homes or other buildings vulnerable to damage, to make a profound psychological impression; and it should be used without warning. Byrnes carried the recommendation to the White House. According to his later recollection, Truman agreed reluctantly because he could think of no alternative.

A harmless technical demonstration had been considered and rejected. The scientists could not identify a demonstration likely to produce the shock needed to force surrender. Probably only one bomb would initially be ready, and there was a risk that it might fail. An advance announcement followed by a failed test, the account observes, could strengthen rather than weaken Japan’s resolve. The panel’s views were not entirely unanimous: some scientists favored a demonstration and worried that using the weapon would prejudice future efforts to outlaw it. The panel nevertheless concluded that it could propose no adequate demonstration and saw no acceptable alternative to direct military use.

The military alternatives were also grave. Truman was considering an invasion and a naval blockade intended to starve Japan into submission. In his diary he framed the choice as whether to invade Japan proper or bomb and blockade, calling it his hardest decision to date. At a June 18 White House meeting, the invasion plan was discussed without mention of the bomb, a silence that struck Stimson’s assistant John J. McCloy as strange. General Marshall proposed a two-phase invasion beginning in November with Kyushu, only 350 miles from Okinawa. He compared its difficulty to Normandy and estimated that the first thirty days could bring losses similar to those on Luzon, about 31,000. Truman had asked for estimates of time and killed and wounded, with American lives taking priority over economy in time or money.

From advice to presidential judgment

The committee’s conclusions were advisory; Stimson emphasized that responsibility for the recommendation rested with him, and the final decision belonged to Truman. Stimson argued that a tremendous shock could persuade the Emperor and military advisers to surrender and save many more American and Japanese lives than the bomb would cost. A city-free demonstration was not, in this reasoning, a neutral middle course: it might fail to produce surrender, while direct use was judged the surest means of ending the killing. The choice thus joined a claim of military necessity to an explicit willingness to target industrial areas where workers’ homes and other buildings could also be damaged.

Truman later recalled that at Potsdam Byrnes, Stimson, William D. Leahy, Marshall, and General Arnold shared the view that the bomb should be used. He said Marshall had stressed the lives an invasion might cost and had estimated at least a quarter of a million American casualties for a landing on the Tokyo plain and elsewhere in Japan. Truman described reaching his own conclusion after long and careful thought and added that he did not like the weapon. The narrative cautions that there may have been no distinct moment when he made up his mind; with the project nearing completion and events moving rapidly, calling it off would have meant breaking with the undertaking’s entire history and momentum.

Civilian destruction and the limits of the decision

The prospect of using the bomb was considered against a background of devastating conventional air raids. Stimson told Truman he did not want the United States to outdo Hitler in atrocities. He was also concerned that conventional bombing might leave Japanese targets too devastated to provide a fair background for demonstrating the atomic weapon’s power. Truman laughed at that formulation, which seemed odd beside Stimson’s moral concern, but said he understood. Neither Stimson nor Marshall questioned whether the bomb should be used; their focus was how to end the slaughter quickly. Truman, meanwhile, upheld civilian control of the war effort as a fundamental principle, wary of military leaders gaining influence over the country’s economy and future political structure.

On August 9, Truman answered a correspondent who urged him to continue the war until Japan accepted unconditional surrender. He acknowledged Japan’s cruelty but rejected the idea that the United States should act in the same manner, expressing regret at the necessity of wiping out whole populations because of their leaders’ stubbornness. He said he would not do so unless it was absolutely necessary, predicted that Japan would soon surrender after the Soviet Union entered the war, and stated that he wanted to save American lives while retaining a human feeling for Japanese women and children. That evening, in a radio address about Potsdam, he urged Japanese civilians to leave industrial cities and save themselves. These statements did not undo the committee’s recommendation or the decision’s momentum, but they show the limits Truman placed on his own justification: military necessity, in his account, did not erase the human cost or make that cost morally indifferent.