Understanding the Decision to Drop the Bomb on Hiroshima and Nagasaki

Aug 10, 2012
By Nathan Donohue

This week marks the 67th anniversary of the nuclear bombings of Hiroshima and Nagasaki. On August 6, 1945, U.S. President Harry Truman informed the world that an atomic weapon had been detonated on the Japanese city of Hiroshima. Nicknamed Little Boy, the bomb with a power of over 20,000 tons of TNT destroyed most of Hiroshima, killing an estimated 130,000 people. Three days later on August 9, a second bomb nicknamed Fat Man was dropped on the Japanese city of Nagasaki destroying most of Nagasaki and killing roughly between 60,000 - 70,000 people. Six days after the bombing of Nagasaki, Japan surrendered, marking the end of World War II.
The destructive power of these nuclear weapons and the subsequent casualties of the Japanese have continued to prompt questions over whether the U.S. should have decided to use these weapons against Japan during World War II. Even 67 years after the event, the decision to drop the first atomic bomb continues to be widely debated.
Certainly, the power of this new weapon was understood before its use against Japan. President Truman stated that “it was the most terrible thing ever discovered.” To that end, the decision to use this new weapon was not taken lightly, nor was it made in a vacuum devoid of dissent, despite what historical accounts may depict. Specifically, historian J. Samuel Walker purports that history has painted a false dichotomy which posited that Truman had to choose between using the atomic bomb and risking hundreds of thousands of American lives. Instead, as Walker highlights in his book “Prompt and Utter Destruction,” the historical records show a much more complex situation.
To be sure, as the development of the atomic bomb was nearing its completion, the U.S. was still engaged in a massive war with the Japanese. By all accounts, from the middle of 1944, it was clear to both the Japanese and the United States that the Japanese were losing the war and that the question was when not if the Japanese would finally capitulate. As the summer of 1945 began, the U.S. military campaign continued to involve numerous aerial raids as well as large scale invasion of Japanese islands. Accordingly, before the atomic bomb became available, the U.S. was planning another large scale invasion of Japan codenamed Operation Downfall for the fall of 1945, which it hoped would overwhelm the Japanese and end the war.
Deciding to Drop the Bomb
In the lead up to the Trinity test, the top priority for President Truman was to end the war as quickly as possible with the fewest U.S. casualties. For many, this had become the overarching purpose for using the atomic bomb once it was completed. Walker notes five reasons why Truman chose to use the bomb.
Ending the war at the earliest possible moment - The primary objective for the U.S. was to win the war at the lowest possible cost. Specifically, Truman was looking for the most effective way to end the war quickly, not for a way to not use the bomb.
To justify the cost of the Manhattan Project - The Manhattan Project was a secret program to which the U.S. had funneled an estimated $1,889,604,000 (in 1945 dollars) through December 31, 1945.
To impress the Soviets - With the end of the war nearing, the Soviets were an important strategic consideration, especially with their military control over most of Eastern Europe. As Yale Professor Gaddis Smith has noted, “It has been demonstrated that the decision to bomb Japan was centrally connected to Truman's confrontational approach to the Soviet Union.” However, this idea is thought to be more appropriately understood as an ancillary benefit of dropping the bomb and not so much its sole purpose.
A lack of incentives not to use the bomb - Weapons were created to be used. By 1945, the bombing of civilians was already an established practice. In fact, the earlier U.S. firebombing campaign of Japan, which began in 1944, killed an estimated 315,922 Japanese, a greater number than the estimated deaths attributed to the atomic bombing of Hiroshima and Nagasaki. The firebombing of Tokyo alone resulted in roughly 100,000 Japanese killed.
Responding to Pearl Harbor - When a general raised objections to the use of the bombs, Truman responded by noting the atrocities of Pearl Harbor and said that “When you have to deal with a beast you have to treat him as a beast.”
Alternatives to dropping the bomb
Nevertheless, until July 1945, the atomic bomb remained untested and the leading plan of the U.S. was to invade Japan through Operation Downfall, beginning with an invasion of the southernmost island of Kyushu in October 1945. In terms of the operation, there were numerous estimates as to the potential U.S. casualties. President Truman received estimates from General MacArthur that upwards of 31,000 U.S. casualties could be expected within the first thirty days. However, other estimates, particularly by the Joint Chiefs, projected casualties to reach almost seven times higher. This is a far cry from the estimate of millions of casualties which has been bandied about in the contemporary media. Nevertheless, Operation Downfall posed a definitive risk to U.S. soldiers.
At the same time, alternatives to both the bomb and the invasion were discussed by the Interim Committee established to advise the manner in which nuclear weapons should be employed against Japan. During these meetings, the Committee discussed three specific alternatives:
Intensifying conventional bombing and the naval blockade - General MacArthur felt that air power alone could force a Japanese surrender within six months with little risk to American lives. However, it was also argued that this may be a best case scenario where in actuality it could take substantially longer.
Allowing the Japanese to retain the Emperor - This plan was predicated on mitigating the call for unconditional surrender by Japan. Both Secretary of War Stimson and Acting Secretary of State Grew felt that this was an essential policy because of the dedication and fanaticism of the Japanese people towards the Emperor Hirohito, whom the Japanese believed to be a deity. 
Waiting for the Soviet Union to enter the war - This had been a primary objective of President Roosevelt in his negotiations with the Soviet Union at the Yalta Conference. Nevertheless, the Committee believed that a Soviet invasion of Manchuria would be helpful but not decisive by itself.
In the summer of 1945, there was a distinctly changing dynamic within Japan. The war had already taken a great toll not just on the Japanese military but also on its entire domestic infrastructure. Japan’s chief cabinet secretary reported in April 1945 that “transportation, shipping, communications, and industry had been so sharply curtailed that the national economy would grind to a virtual standstill,” factors that he predicted would become acute by the end of the year. The destruction of Japanese cities through the repeated raids by U.S. B-29’s, had caused conditions in Japan to diminish with an evaporating food supply and decreasing public morale. As General Robert Eichelberger, a lieutenant of General MacArthur, wrote on July 24 of that year, “a great many people, probably 50%, feel that Japan is about to fold up.”
To that end, if Hirohito’s decision to end the war after the bombing of Nagasaki and Hiroshima was predicated on the desire to save the Japanese people, then the declining situation already evident in Japan could have produced a similar decision to surrender without the use of the atomic bomb and that the alternative of intensifying conventional bombing and the naval blockade would only have increased the likelihood.
In addition, the alternative idea of modifying unconditional surrender could have proved effective as well. By June 1945 there were already divisions within the Japanese Supreme Council discussing how to end the war with the Americans with the largest reservation being the desire to retain the national polity by allowing the Emperor Hirohito to remain on his throne. In fact, in July 1945 the U.S. intercepted a Japanese cable from Japan’s Foreign Minister Togo to Japan’s ambassador to the Soviet Union which stated that Japan wanted to end the war and that the major impediment to Japanese surrender was the insistence on unconditional surrender by the U.S. Concurrently, the U.S. was also deliberating offers of surrender for the Japanese. Secretary of War Stimson, aware of the Japanese regard for the Emperor, was adamant that the offer include the provision that the Emperor would be able to remain in power. However, he was continually overridden and even with the knowledge that such a modification could prove amenable to the Japanese government, the U.S. chose not to include it.
The third alternative of waiting for the Soviet Union to enter the war, presents an interesting issue in that it actually occurred and it remains unclear what effect this had on the Japanese decision to surrender. President Truman himself remarked in his diary on July 17, 1945, “Fini Japs when that [Soviet entry into the war] comes about.” Between when the first atomic bomb was dropped on Hiroshima and before the Japanese had decided to surrender, the Soviet Union entered the war by invading Japanese-held Manchuria from the north, routing the Japanese army there. Historian Tsuyoshi Hasegawa argues that it wasn’t until the Soviet invasion that the Emperor “was finally convinced that the moment had at last arrived to end the war.” If this is true, then it could mean that in connection with the bombing of Hiroshima, the Committee’s assumption that a Soviet invasion would be helpful but not decisive was correct, or instead, that it was just the opposite and that the Soviet invasion was the decisive act to facilitate a Japanese surrender.
In the end, none of these alternatives were chosen. However, it does not rule out their possible efficacy nor does it mean that the atomic bomb was the only way to produce surrender by the Japanese.
Additional Considerations
In terms of dropping the bomb, there were also various ideas for how it should be used against the Japanese. This included the argument that it could be used specifically for targeting a military objective such as a collection of factories and that the civilians around the target area should be warned before its use. Similarly, the idea was suggested that an outside demonstration be made to the Japanese so that they could witness the power of the weapon before suffering its use. However, neither Oppenheimer nor the military planners believed that a demonstration of the weapon would be sufficient to create a Japanese surrender. More so, they worried that any warning of the weapons usage would undermine the U.S. position if the weapon eventually failed to work.
Another significant factor that I believe is continually overlooked is the issue of Kyoto. Kyoto was the ancient capital of Japan which held a deep and powerful connection among the Japanese people. When the original bombing plans were developed by General Groves and other U.S. officials, they continually noted Kyoto as their preferred military target. Stimson, understanding the Japanese culture and the significance of such an attack, unilaterally ruled out Kyoto as a target stating that if it were bombed, the Japanese would fight to the last man and would never surrender. The significance of this is that although it is generally accepted that the bombings of Hiroshima and Nagasaki caused the Japanese surrender, if one of the targets had actually been Kyoto, then the event that marked the end of the war may have instead created a resurgence of Japanese will to fight.
The purpose of this paper is not to argue counterfactuals but is instead intended to highlight the complexities of the situation. It is clear that there were multiple reasons for using the atomic bomb, but that at the same time there were also alternatives which may have proved equally effective in prompting a Japanese surrender. One could argue that by just modifying unconditional surrender, the U.S. could have saved both U.S. lives and the lives of those Japanese residing in Hiroshima and Nagasaki. As noted in the biography of Henry Stimson, “history might find that the United States, by its delay in stating its position [in regards to the Emperor] had prolonged the war.” Similarly, it can be argued that correlation does not equal causation and that as Hasegawa suggests, maybe the decisive factor was having the engagement of the Soviet Union, and not the dropping of the two bombs. Or, as Walker noted, it seems reasonable to conclude that “a combination of B-29 raids with conventional bombs, the blockade, the Soviet invasion, and perhaps a moderation of unconditional surrender policy would have ended the war without an invasion and without the use of atomic bombs.” 
Regardless, Truman decided to use nuclear weapons on both Hiroshima and Nagasaki and days after the bombing of Nagasaki the Japanese did indeed surrender bringing an end to World War II.  
Nathan Donohue is a research intern for the Project on Nuclear Issues. The views expressed above are his own and do not necessarily reflect those of the Center for Strategic and International Studies or the Project on Nuclear Issues.