The Bombing of Hiroshima: Facts & Aftermath

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  • 0:01 Historical Background
  • 0:49 The Manhattan Project
  • 1:52 Why Hiroshima?
  • 4:34 August 6, 1945
  • 6:16 Aftermath
  • 7:42 Lesson Summary
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Lesson Transcript
Instructor: Mark Pearcy

Mark has a Ph.D in Social Science Education

The use of an atomic weapon on the Japanese city of Hiroshima in August 1945 hastened the end World War II. In this lesson, we'll explore the factors that influenced America's decision to use the atomic bomb, as well the consequences of its use.

Historical Background

In August of 1939, Albert Einstein wrote a letter to President Franklin Roosevelt. It was an odd letter, in which Einstein tried to describe an astoundingly complex idea in easy-to-understand language:

'It may be possible to set up a nuclear chain reaction in a large mass of uranium, by which vast amounts of power… would be generated. This new phenomenon would also lead to the construction of bombs.'

Einstein advised the president that a single bomb of this type 'might very well destroy' an entire city. He also pointed out that Germany was seemingly in the process of hoarding their own stores of uranium, meaning they might be able to develop their own bomb first. This was the beginning of a long road that would lead to the destruction of Hiroshima.

The Manhattan Project

Einstein's theory was sound, and the only questions left were practical: what fuel would work best? How would scientists construct the bomb? How devastating would it actually be? These questions drove the research behind the Manhattan Project, the code name for the enormous initiative to build an atomic weapon. The project was overseen by General Leslie Groves, the project's military commander and Dr. Robert Oppenheimer, its scientific director. The bulk of the project's work took place in Los Alamos, New Mexico.

By July 1945, project members had a model ready to test. However, scientists remained unsure how much explosive energy might be released during the explosion. One bet that the explosion would ignite every molecule in the atmosphere and effectively destroy all human life. Another wagered that the bomb would demolish most of New Mexico. The explosion that followed did not destroy all human life, but it was clear that Einstein's original prediction was fundamentally correct.

Why Hiroshima?

After the initial test in May 1945, scientists at Los Alamos readied two prototypes they nicknamed 'Fat Man' and 'Little Boy.' The former had a plutonium core; the latter was a uranium bomb and considered the more reliable of the two. The bombs were ready; now military and government officials had to choose a target.

The U.S. Army asked General Groves to create a list of potential Japanese cities for targeting. In partnership with a council made up of military officers and scientists, the Target Committee came up with five potential areas: the relatively undamaged cities of Kokura, Yokohama, Niigata, Kyoto and Hiroshima. In light of its status as Japan's ceremonial capital, Kyoto was later replaced by Nagasaki.

Though it's unclear what role it played in the decision to use the bomb, an important consideration was America's future relationship with the Soviet Union. Although the United States and the Soviet Union had been allies during most of World War II, American officials were acutely aware that the relationship was entirely based on a common enemy: Nazi Germany. Once the war was over, the United States and the Soviet Union would be the only remaining global superpowers.

While the Los Alamos test was being conducted, President Harry Truman, who had replaced President Franklin Roosevelt after the latter's death in April 1945, was in Potsdam, Germany, negotiating the state of the postwar world with Josef Stalin. If the Soviets saw the A-bomb used in combat, they would understand the power of America's new weapon. As it happened, Stalin already knew - he had an extensive spy network at Los Alamos who had informed him about the bomb's development.

Once the decision was reached to use the bomb, several of the scientists who had built it, most notably Leo Szilard, a Hungarian-born physicist and one of the earliest involved in its construction, tried to convince President Truman that the bomb was too horrible to use. Seventy of the scientists wrote a letter, known as the Szilard Petition, in which they offered an alternative idea of giving Japan a demonstration of the weapon's power before using it on an inhabited area, among other ideas.

But the idea, if it ever reached Truman's ears, was rejected out-of-hand. One argument referred to the ability of Japan's air defenses, heavily degraded as they were, to stop a demonstration. Additionally, scientists were still uncertain if the bomb would even work. But more than that, the decision about which cities to target had already been debated and decided, without input from the bomb's creators.

August 6, 1945

On August 6, 1945, a single B-29 Superfortress left the island of Tinian in the Pacific Ocean. Called the Enola Gay after the mother of the pilot, Colonel Paul Tibbets, the plane flew six hours to the Japanese mainland and the city of Hiroshima.

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