Several committees played key roles in determining how and where the atomic bombs would be dropped on Japan.
The Interim Committee
As the Manhattan Project neared completion, there was a growing sentiment among project leaders that an advisory committee to make recommendations relating to nuclear energy should be created. In response to these concerns, in May 1945 Secretary of War Henry L. Stimson, with the approval of President Harry Truman, established the Interim Committee. The committee was so named because it was an interim, or temporary body, that would last until a more formal organization dealing with nuclear issues was created.
Although the use of the atomic bomb in World War II was not an explicit concern of the committee when it was established, the pressing matter of the Pacific war, the approaching success of the Manhattan Project and the occupations of the Interim Committee's members inevitably led to a discussion of the issue.
Initially, the committee considered targets including Kyoto, Hiroshima, Yokohama, the Kokura Arsenal, and Niigata. Kyoto and Hiroshima were considered "AA" targets because of the former's status as an "intellectual center" that would better "appreciate" the significance of the bomb and because of the latter's role as an important army depot. The idea of bombing the Japanese emperor's palace was set aside, as it was uncertain how militarily feasible this would be.
The committee also established that the bomb's power as a psychological weapon should be exploited to its fullest extent:
A. It was agreed that psychological factors in the target selection were of great importance. Two aspects of this are (1) obtaining the greatest psychological effect against Japan and (2) making the initial use sufficiently spectacular for the importance of the weapon to be internationally recognized when publicity on it is released.
B. In this respect Kyoto has the advantage of the people being more highly intelligent and hence better able to appreciate the significance of the weapon. Hiroshima has the advantage of being such a size and with possible focusing from nearby mountains that a large fraction of the city may be destroyed. The Emperor's palace in Tokyo has a greater fame than any other target but is of least strategic value.
On June 1, the committee came to a consensus regarding the bomb's use: "[James F.] Byrnes recommended, and the Committee agreed, that the Secretary of War should be advised that while recognizing that the final selection of the target was essentially a military decision, the present view of the Committee was that the bomb should be used against Japan as soon as possible; that it be used on a war plant surrounded by workers’ homes; and that it be used without prior warning.
After the committee reached this conclusion, Byrnes went to inform Truman of the outcome. The president reportedly agreed with the group's decision.
On June 1, 1945, the Interim Committee concluded that the atomic bomb should be used as soon as possible against Japan, with no prior warning, on a target of military significance. Soon after Arthur H. Compton reported these findings at the Chicago Met Lab, a group of Met Lab scientists led by physicist James Franck founded a committee to study the question of the bomb's use.
On June 11, the committee released its findings, which were mainly written by Eugene Rabinowitch and influenced by Leo Szilard. To begin with, the report categorically stated that other countries would eventually acquire nuclear weapons. As a result of this inevitability, the committee continued, a peaceful demonstration of the atomic bomb would make the political climate more favorable to the international control of nuclear weapons. Some of their conclusions included:
“Nuclear bombs cannot possibly remain a ‘secret weapon’ at the exclusive disposal of this country for more than a few years. The scientific facts on which construction is based are well known to scientists of other countries. Unless an effective international control of nuclear explosives is instituted, a race for nuclear armaments is certain to ensue following the first revelation of our possession of nuclear weapons to the world. Within ten years, other countries may have nuclear bombs, each of which, weighing less than a ton, could destroy an urban area of more than ten square miles. In the war to which such an armaments race is likely to lead, the United States, with its agglomeration of population and industry in comparatively few metropolitan districts, will be at a disadvantage compared to nations whose populations and industry are scattered over large areas.
We believe that these considerations make the use of nuclear bombs for an early unannounced attack against Japan inadvisable. If the United States were to be the first to release this new means of indiscriminate destruction upon mankind, she would sacrifice public support throughout the world, precipitate the race for armaments and prejudice the possibility of reaching an international agreement on the future control of such weapons.
Much more favorable conditions for the eventual achievement of such an agreement could be created if nuclear bombs were first revealed to the world by a demonstration in an appropriately selected uninhabited area.”
Leo Szilard, with James Franck accompanying him, traveled to Washington, DC to present the report to Secretary of War Henry Stimson the next day, on June 12. However, a Stimson aide untruthfully told the men that he was away from the capital. Instead, Franck and Szilard presented the report to one of the secretary's assistants. Arthur H. Compton further lessened the report's impact by attaching a cover sheet criticizing the committee members for not taking into account "the probable net saving of many lives" if the bombs were used.
It is uncertain if Stimson ever saw the Franck Report at all. In any event, it was overridden by The Interim Committee's previous June 1 conclusion that the bomb "be used against Japan as soon as possible... without prior warning," as well as the June 16 findings of the Scientific Panel of the Interim Committee that "we see no acceptable alternative to direct military use."
The Interim Committee was also advised by a Scientific Panel. On June 16, they came to their own conclusions regarding the bomb's use, opposing the findings of the Franck Report, which five days earlier had supported a demonstration of the bomb before its use.
“The opinions of our scientific colleagues on the initial use of these weapons are not unanimous: they range from the proposal of a purely technical demonstration to that of the military application best designed to induce surrender. Those who advocate a purely technical demonstration would wish to outlaw the use of atomic weapons, and have feared that if we use the weapons now our position in future negotiations will be prejudiced. Others emphasize the opportunity of saving American lives by immediate military use, and believe that such use will improve the international prospects, in that they are more concerned with the prevention of war than with the elimination of this specific weapon. We find ourselves closer to these latter views; we can propose no technical demonstration likely to bring an end to the war; we see no acceptable alternative to direct military use."
A Target Committee convened in April and May 1945 to select a short list of Japanese cities to be removed from conventional bombing missions as possible atomic bomb candidates. The committee was chaired by Brigadier General Thomas Farrell, who represented the Manhattan Project as Groves’ deputy. Other members included two Air Force officers – a major and colonel – and five scientists including John von Neumann and British physicist William G. Penney.
By the end of July the list included Hiroshima, Kokura, Niigata and Nagasaki. Earlier, Secretary of War Henry Stimson had vetoed the ancient capital Kyoto, with its magnificent shrines and temples, because of its cultural importance to the Japanese people.
On July 25, 1945, official orders were issued to the 509th Composite Group to "deliver its first special bomb as soon as weather will permit visual bombing after about August 3, 1945 on one of the targets. . . . Additional bombs will be delivered on the above targets as soon as made ready by project staff."
The Potsdam Proclamation issued by the United States, China, and Great Britain on July 26, 1945 called for Japan's immediate unconditional surrender. The alternative, the allies warned, was "complete and utter destruction." Three days later, on July 29th, the Japanese rejected it, encouraging their citizens to "mokusatsu" (which means "ignore it"). This would set the stage for the bombing of Hiroshima and Nagasaki.