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# The Manhattan Project and the atomic bomb

AP.USH:
KC‑7.3.III.D (KC)
,
Unit 7: Learning Objective M
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WOR (Theme)
In 1945, the United States dropped two atomic bombs on Japan, ending World War II.

## Overview

• The United States detonated two atomic bombs over the Japanese cities of Hiroshima and Nagasaki in August 1945, killing 210,000 people—children, women, and men.
• President Truman authorized the use of the atom bombs in an effort to bring about Japan’s surrender in the Second World War. In the days following the bombings Japan surrendered.
• The Manhattan Project was the US government program during World War II that developed and built these first atomic bombs.
• Detonation of these first nuclear bombs signaled arrival of a frightening new Atomic Age.

## The Manhattan Project

The Manhattan Project was the codename for the secret US government research and engineering project during the Second World War that developed the world’s first nuclear weapons. President Franklin Roosevelt created a committee to look into the possibility of developing a nuclear weapon after he received a letter from Nobel Prize laureate Albert Einstein in October 1939. In his letter, Einstein warned the president that Nazi Germany was likely already at work on developing a nuclear weapon. By August 1942, the Manhattan Project was underway.start superscript, 1, end superscript
Photograph of Albert Einstein and J. Robert Oppenheimer.
Albert Einstein and J. Robert Oppenheimer. Einstein warned that the Germans were researching an atomic bomb and suggested that the United States do the same. Oppenheimer was the leading scientist at Los Alamos National Laboratory. Image courtesy Wikimedia Commons.
By 1944, six thousand scientists and engineers from leading universities and industrial research labs were at work on the development of the world’s first-ever nuclear weapon. Robert Oppenheimer, a physicist, headed the Los Alamos National Laboratory, the Manhattan Project’s principal research and development facility. For security reasons, the facility was located in the desert near Los Alamos, New Mexico.
Major General Leslie Groves oversaw the Manhattan Project for the US government. Private corporations, foremost among them DuPont, helped prepare weapons-grade uranium and other components needed to make the bombs. Nuclear materials were processed in reactors located in Oak Ridge, Tennessee and Hanford, Washington. At its peak, the Manhattan Project employed 130,000 Americans at thirty-seven facilities across the country.
On July 16, 1945 the first nuclear bomb was detonated in the early morning darkness at a military test-facility at Alamogordo, New Mexico. The intense brightness of the explosion’s flash was followed by the rise of a large mushroom cloud from the desert floor. House windows more than fifty miles away shattered.

## Hiroshima and Nagasaki

In May 1945, the Allies defeated Germany, two months before the atomic bomb was complete. War with Japan continued, however, and In August 1945 it seemed that an invasion of Japan itself might be necessary to force the Japanese to surrender. Military advisers to President Harry S. Truman warned that such a ground war would result in the deaths of tens or hundreds of thousands of young men in the US Armed Forces, as well as the deaths of many Japanese military personnel and civilians. After receiving no reply to his threat that "prompt and utter destruction" would follow if the Japanese did not surrender unconditionally, Truman authorized the use of the bomb on Japan.squared
On August 6, 1945 an American B-29 bomber named the “Enola Gay” dropped the first atomic bomb on the city of Hiroshima. The device exploded over the city with a force of 12,500 tons of TNT. “[The city] had been there just a few minutes before . . . but it was absolutely gone,” said one witness. About 140,000 people were killed instantly or died due to injury or radiation poisoning within months of the blast at Hiroshima.cubed
Photograph of the mushroom cloud following the atomic bombing of Nagasaki, Japan.
Mushroom cloud following the atomic bombing of Nagasaki, Japan. Image courtesy National Archives.
Truman called for surrender the day after the bombing at Hiroshima once more, but once more the Japanese government refused. On August 9, about 80,000 people died after the United States dropped a second bomb on the Japanese city of Nagasaki. A total of 210,000 civilians died in the two atomic blasts. (In comparison, the United States had killed 120,000 Japanese civilians with conventional bombs during air raids on Tokyo in March 1945.)start superscript, 4, end superscript
Six days later, after the Soviet Union declared war on Japan, the Japanese government signed an unconditional surrender. World War II was over.
The development of the atomic bomb had repercussions that would continue to resonate throughout the twentieth century, particularly in the Cold War. Spies within the research and development facility at Los Alamos—most notably the scientist Klaus Fuchs—gave the Soviet Union information about the nuclear program that helped the Soviets develop their own atomic weapon by 1949.start superscript, 5, end superscript

## Was the bombing of Hiroshima and Nagasaki necessary?

Truman’s decision was framed by his belief that the bombing of Hiroshima and Nagasaki would shorten the war and thereby save the lives of tens or hundreds of thousands of American soldiers as well as untold numbers of Japanese soldiers and citizens.
However, in the years following the war—and to this day—the United States’ use of nuclear bombs against the civilian populations of Hiroshima and Nagasaki has had both proponents and detractors. Many questions remain about the necessity of using the bomb and its moral implications: Would the United States have acted so quickly to use nuclear weapons against Europeans? Was racism against the Japanese an element in the decision? Might the United States have exploded a nuclear bomb on an uninhabited island to demonstrate the bomb’s terrible power instead of destroying two cities? Might the United States have been able to gain Japan’s unconditional surrender by other means?
But there was no question that the development and use of the atomic bomb changed the nature of world warfare forever. Though the bombings of Japan remain the only wartime use of nuclear weapons, since 1945 the threat of nuclear war has loomed over international conflicts, promising a level of "prompt and utter destruction" never before seen in the world.

## What do you think?

What might have happened if Nazi Germany had developed a nuclear weapon before the United States?
In what ways did scientists, engineers, corporate leaders, American workers, and the military come together in shaping the successes of the Manhattan Project?
Was the decision to drop the atom bombs on civilians morally justifiable?

## Want to join the conversation?

• How did they even make the bomb?
• The way the bomb works is this: inside of the bomb, an atom is split. When aforementioned atom is split, massive amounts of energy are released. It can be achieved by bringing an element to "critical mass," which means that it's so dense that it can't be packed any tighter. This process is called "nuclear fission." There are two types of bombs that were dropped.
The first bomb, which was used on Hiroshima, "Little Boy," was a Uranium-235 gun-type fission weapon. Basically, a small explosive in the back launches a hollow uranium "bullet" to the front of the bomb, where a target cylinder or spike of sorts is waiting for it. Once the "bullet" has struck the spike at the front, the atoms split, causing an explosion, along with a mushroom cloud.
The bomb that was used on Nagasaki, "Fat Man," was an imploding-type bomb that was more powerful, as well as complex. The material that fueled it was Plutonium-239. Conventional explosive, surrounded by Uranium-238, were placed around the plutonium core, and when they exploded, they sent a shock wave of energy and force, which was reflected by the U-238 by its neutron reflecting properties, to the aforementioned core, causing it to undergo nuclear fission. Estimates say that only about 20% of the 13.6 pound P-239 core underwent fission, throwing the other 11 pounds away, scattered in the nearby areas.
Sorry for the over-detailed paragraphs and complex wording. I hope this helps! :)
• The Atomic Bombings were necessary to end the war quickly with the least amount of bloodshed. Truman chose the atomic bombs over an invasion of the home islands of Japan, these invasions were called Operation Olympic and Coronet, classified under Operation Downfall. Operation Olympic, planed to commence in Nov. 1945 focused on taking Kyushu island while Coronet focused on taking the areas around Tokyo in Spring, 1946. Operation Downfall would oversee these invasions and would provide logistical support.

These invasions would have resulted in the deaths of millions of allied troops and an larger, untold number of Japanese military personnel and civilians. In fact, the Japanese Government formed a National Militia to defend the home islands in case of invasion. To quote President Truman, he knew that an invasion of the Japanese home islands would be an "Okinawa from one end of Japan to the other." a bloody struggle. The Japanese sought to perform Ketsu-go or "Decisive Battle" to weaken the allied advance, if not outright destroy it, and force the allies to retreat. Every able man, woman and child were armed with what was left of the available arms. Schoolgirls were taught how to fire, reload and maintain standard issue combat rifles to defend the home islands, an entire air wing was in reserve to use as Kamikaze attack planes to disrupt shipping and to sink landing craft. An invasion would have been a bloodbath, a devastating ordeal for both of the sides involved in it. The Atomic Bombs ended the war a good few months ahead of schedule, and saved countless lives.
• However, many people can argue that these drops were partially pushed through by racism. As noted in the article above, would the US be so ready to drop it on Germany? Or Italy? Imagine the war from the Japanese perspective. They created an empire, similar the the British, and they fought to defend it. Then someone halfway across the world killed 250,000 of your people in one stroke. What if Japan had killed 250,000 people in the USA? Bombed New York or Chicago? Surely the USA would revolt.
• Didn't the Japanese want to surrender? If they could have kept their Emperor they would have surrendered months before they were bombed, right?
• look, steven.strange12, I have no idea what the japanese were thinking, but I think it's safe to conclude that the leaders at the time were a little crazy. Also, the japanese government went kinda over the edge and started convincing japanese citizens that their Emperor was a god. these convinced soliders and generals would not surrender because they thought they were serving a god
• How did the Americans decide on those two particular cities to bomb? I understand why they didn't want to destroy Tokyo, but were there other options than Hiroshima and/or Nagasaki?
• if they bombed Tokyo, the Japanese would retaliate blindly, but by bombing these cities, the us got the message across without extra bloodshed
• *What might have happened if Nazi Germany had developed a nuclear weapon before the United States?

I think that eventually Germany would be beaten, good always triumphs over evil, but the world, America, would be a very different place than it is now. Any other theories or ideas?

*What would have happened if the Axis powers would have won?
Thoughts are appreciated!
• If Nazi Germany had developed a nuclear bomb then the world as we know would probably not exist right now. Hitler enjoyed killing people and would've bombed everyone thus destroying the other nations and the war. He would've won and eventually he would turn around and destroy his own allies in the war to create a German only world. -----At least that is my speculations to what could've happened.
• Does anybody know how this affected society
• The fear of nuclear war also affected people in the US.

With Cold War tensions escalating in the 1950s, the threat of a Soviet nuclear attack cast a terrifying shadow over everyday American life. In schools, children learned to “duck and cover,” diving under their desks and staying far away from windows in drills designed to protect them during an atomic strike. Families across the country (at least those who could afford it) built fallout shelters in their basements and backyards. Community shelters were constructed beneath municipal buildings, and emergency government bunkers were carved into hillsides.
...
During the crisis over Berlin in mid-1961, President John F. Kennedy expanded the nation’s civil defense programs, calling for more than \$200 million in appropriations for the construction of public fallout shelters in the United States. Kennedy also encouraged Americans to build private shelters, the estimated number of which rose from 60,000 in June 1961 to some 200,000 in 1965.

https://www.history.com/news/cold-war-fallout-shelter-survival-rations-food
• Why was the atomic bomb created?
• President Truman authorized the use of the atom bombs in an effort to bring about Japan's surrender in the Second World War. In the days following the bombings Japan surrendered. The Manhattan Project was the US government program during World War II that developed and built these first atomic bombs.