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National Museum of Nuclear Science & History

Stimson on the Bomb

In the February 1947 issue of Harper’s Magazine, Secretary of War Henry Stimson provided the American public with his rationale for using the atomic bomb. President of Harvard University James B. Conant, an important scientific advisor to the Manhattan Project, urged Stimson to respond to growing criticism of use of the atomic bombs. Stimson’s article documents the refusal of the Japanese to surrender and estimates that the Allied invasion would have cost one million American casualties and many more Japanese. 

Document Type:
Nagasaki before and after the bombing

From “The Decision to Use the Atomic Bomb” by Henry Stimson

In recent months there has been much comment about the decision to use atomic bombs in attacks on the Japanese cities of Hiroshima and Nagasaki. This decision was one of the gravest made by our government in recent years, and it is entirely proper that it should be widely discussed. I have therefore decided to record for all who may be interested my understanding of the events which led up to the attack on Hiroshima on August 6, 1945, on Nagasaki on August 9, and the Japanese decision to surrender on August 10. No single individual can hope to know exactly what took place in the minds of all of those who had a share in these events, but what follows is an exact description of our thoughts and actions as I find them in the records and in my clear recollection.


The extraordinary story of the successful development of the atomic bomb has been well told elsewhere. As the time went on it became clear that the weapon would not be available in time for use in the European Theater, and the war against Germany was successfully ended by the use of what are now called conventional means. But in the spring of 1945 it became evident that the climax of our prolonged atomic effort was at hand.


The principal political, social, and military objective of the United States in the summer of 1945 was the prompt and complete surrender of Japan. Only the complete destruction of her military power could open the way to lasting peace. Japan, in July 1945, had been seriously weakened by our increasingly violent attacks. It was known to us that she had gone so far as to make tentative proposals to the Soviet government, hoping to use the Russians as mediators in a negotiated peace. These vague proposals contemplated the retention of Japan of important conquered areas and were therefore not considered seriously. There was as yet no indication of any weakening in the Japanese determination to fight rather than accept unconditional surrender. If she should persist in her fight to the end, she had still a great military force.

In the middle of July 1945, the intelligence section of the War Department General Staff estimated Japanese military strength as follows: in the home islands, slightly under 2,000,000; in Korea, Manchuria, China proper, and Formosa, slightly over 2,000,000; in French IndoChina, Thailand, and Burma, over 200,000; in the East Indies area, including the Philippines, over 500,000; in the bypassed Pacific islands, over 100,000. The total strength of the Japanese Army was estimated at about 5,000,000 men. These estimates later proved to be in very close agreement with official Japanese figures. The Japanese Army was in much better condition than the Japanese Navy and Air Force. The Navy had practically ceased to exist except as a harrying force against an invasion fleet. The Air Force had been reduced mainly to reliance upon Kamikaze, or suicide, attacks. These latter, however, had already inflicted serious damage on our seagoing forces, and their possible effectiveness in a last ditch fight was a matter of real concern to our naval leaders.

As we understood it in July, there was a very strong possibility that the Japanese government might determine upon resistance to the end, in all the areas of the Far East under its control. In such an event the Allies would be faced with the enormous task of destroying an armed force of five million men and five thousand suicide aircraft, belonging to a race which had already amply demonstrated its ability to fight literally to the death.

The strategic plans of our armed forces for the defeat of Japan, as they stood in July, had been prepared without reliance upon the atomic bomb, which had not yet been tested in New Mexico. We were planning an intensified sea and air blockade, and greatly intensified strategic air bombing, through the summer and early fall, to be followed on November 1 by an invasion of the southern island of Kyushu. This would be followed in turn by an invasion of the main island of Honshu in the spring of 1946. The total U.S. military and naval force involved in this grand design was of the order of 5,000,000 men; if all those indirectly concerned are included, it was larger still.

We estimated that if we should be forced to carry this plan to its conclusion, the major fighting would not end until the latter part of 1946, at the earliest. I was informed that such operations might be expected to cost over a million casualties, to American forces alone. Additional large losses might be expected among our allies, and, of course, if our campaign were successful and if we could judge by previous experience, enemy casualties would be much larger than our own.

It was already clear in July that even before the invasion we should be able to inflict enormously severe damage on the Japanese homeland by the combined application of “conventional” sea and air power. The critical question was whether this kind of action would induce surrender. It therefore became necessary to consider very carefully the probable state of mind of the enemy, and to assess with accuracy the line of conduct which might end his will to resist.


There was much discussion in Washington about the timing of the warning to Japan. The controlling factor in the end was the date already set for the Potsdam meeting of the Big Three. It was President Truman’s decision that such a warning should be solemnly issued by the U.S. and the U.K. from this meeting, with the concurrence of the head of the Chinese government, so that it would be plain that all of Japan’s principal enemies were in entire unity. This was done in the Potsdam ultimatum of July 26, which very closely followed the above memorandum of July 2 with the exception that it made no mention of the Japanese Emperor. On July 28 the Premier of Japan, Suzuki, rejected the Potsdam ultimatum by announcing that it was “unworthy of public notice.” In the face of this rejection we could only proceed to demonstrate that the ultimatum had meant exactly what it said when it stated that if the Japanese continued the war, “the full application of our military power, backed by our resolve, will mean the inevitable and complete destruction of the Japanese armed forces and just as inevitably the utter devastation of the Japanese homeland.”

For such a purpose the atomic bomb was an eminently suitable weapon. The New Mexico test occurred while we were at Potsdam, on July 16. It was immediately clear that the power of the bomb measured up to our highest estimates. We had developed a weapon of such a revolutionary character that its use against the enemy might well be expected to produce exactly the kind of shock on the Japanese ruling oligarchy which we desired, strengthening the position of those who wished peace, and weakening that of the military party.

Because of the importance of the atomic mission against Japan, the detailed plans were brought to me by the military staff for approval. With President Truman’s warm support I struck off the list of suggested targets the city of Kyoto. Although it was a target of considerable military importance, it had been the ancient capital of Japan and was a shrine of Japanese art and culture. We determined that it should be spared. I approved four other targets including the cities of Hiroshima and Nagasaki.

Hiroshima was bombed on August 6, and Nagasaki on August 9. These two cities were active working parts of the Japanese war effort. One was an army center; the other was naval and industrial. Hiroshima was the headquarters of the Japanese Army defending southern Japan and was a major military storage and assembly point. Nagasaki was a major seaport and it contained several large industrial plants of great wartime importance. We believed that our attacks had struck cities which must certainly be important to the Japanese military leaders, both Army and Navy, and we waited for a result. We waited one day.

Many accounts have been written about the Japanese surrender. After a prolonged Japanese cabinet session in which the deadlock was broken by the Emperor himself, the offer to surrender was made on August 10. It was based on the Potsdam terms, with a reservation concerning the sovereignty of the Emperor. While the Allied reply made no promises other than those already given, it implicitly recognized the Emperor’s position by prescribing that his power must be subject to the orders of the Allied Supreme Commander. These terms were accepted on August 14 by the Japanese, and the instrument of surrender was formally signed on September 2, in Tokyo Bay. Our great objective was thus achieved, and all the evidence I have seen indicates that the controlling factor in the final Japanese decision to accept our terms of surrender was the atomic bomb.

The two atomic bombs which we had dropped were the only ones we had ready, and our rate of production at the time was very small. Had the war continued until the projected invasion on November 1, additional fire raids of B-29s would have been more destructive of life and property than the very limited number of atomic raids which we could have executed in the same period. But the atomic bomb was more than a weapon of terrible destruction; it was a psychological weapon. In March 1945 our Air Force had launched its first great incendiary raid on the Tokyo area. In this raid more damage was done and more casualties were inflicted than was the case at Hiroshima. Hundreds of bombers took part and hundreds of tons of incendiaries were dropped. Similar successive raids burned out a great part of the urban area of Japan, but the Japanese fought on. On August 6 one B-29 dropped a single atomic bomb on Hiroshima. Three days later a second bomb was dropped on Nagasaki and the war was over. So far as the Japanese could know, our ability to execute atomic attacks, if necessary by many planes at a time, was unlimited. As Dr. Karl Compton has said, “it was not one atomic bomb, or two, which brought surrender; it was the experience of what an atomic bomb will actually do to a community, plus the dread of many more, that was effective.”

The bomb thus served exactly the purpose we intended. The peace party was able to take the path of surrender, and the whole weight of the Emperor’s prestige was exerted in factor of peace. When the Emperor ordered surrender, and the small but dangerous group of fanatics who opposed him were brought under control, the Japanese became so subdued that the great undertaking of occupation and disarmament was completed with unprecedented ease.

In the foregoing pages I have tried to give an accurate account of my own personal observations of the circumstances which led up to the use of the atomic bomb and the reasons which underlay our use of it. To me they have always seemed compelling and clear, and I cannot see how any person vested with such responsibilities as mine could have taken any other course or given any other advice to his chiefs.

More Historical Resources:

Surrender of Japan.

Truman announces Japanese surrender.

Japanese Tank knocked out of action on Tinian