August 9, 1945: the mushroom cloud from the atomic bomb dropped by the U.S. on Nagasaki, Japan

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The Dawn of the Atomic Age

Tensions between the United States and North Korea over nuclear weapons have roots in a historic U.S. government effort called the Manhattan Project

December 11, 2017
By Bryan Brown

North Korea’s dictator, Kim Jong Un, vows to wipe out the U.S. with a “hail of fire.” U.S. President Donald Trump threatens to “totally destroy” North Korea. Those tensions have brought the world closer to a nuclear conflict than at any time since the end of the Cold War (1947-1991).

Such a conflict could have horrific consequences. The use of a single nuclear weapon could level whole cities and kill millions of people.

Kim Jong Un is North Korea’s dictator. He promises to wipe out the U.S. with a “hail of fire.” U.S. President Donald Trump threatens to “totally destroy” North Korea. Those tensions have brought the world closer to a nuclear conflict than at any time since the end of the Cold War (1947-1991).

Such a conflict could have terrible consequences. The use of a single nuclear weapon could level whole cities. It could kill millions of people.

Where did such monstrous firepower come from? It all began 75 years ago, in September 1942, when the U.S. Army took charge of a top-secret effort: the Manhattan Project. Its goal was to produce a powerful new weapon that could be used against America’s enemies in World War II (1939-1945). The result would be the world’s first atomic bomb. 

In 1945, U.S. warplanes dropped two atom bombs, on the Japanese cities of Hiroshima and Nagasaki. The devastation brought Japan to its knees and ended the war. The bomb also changed the nature of warfare forever.  

Today, as nuclear fears again make headlines, we’re still grappling with the destructive power that the Manhattan Project unleashed.

Where did such terrible firepower come from? It all began 75 years ago, in September 1942. That was when the U.S. Army took charge of a top-secret effort called the Manhattan Project. Its goal was to produce a powerful new weapon that could be used against America’s enemies in World War II (1939-1945). The result would be the world’s first atomic bomb.

In 1945, U.S. warplanes dropped two atom bombs. They were dropped on the Japanese cities of Hiroshima and Nagasaki. The damage brought Japan to its knees and ended the war. The bomb also changed the nature of warfare forever.

Today, nuclear fears again make headlines. We are still struggling with the destructive power that the Manhattan Project unleashed.

The German Threat

World War II began in Europe when German dictator Adolf Hitler attacked Poland in September 1939. Only a month earlier, physicist Albert Einstein had written to U.S. President Franklin D. Roosevelt, warning that German scientists might be using new advances in physics to engineer a nuclear weapon. 

Building such a weapon would involve splitting the nucleus of an atom, a process called fission. Using the element uranium, this process could cause a chain reaction that would unleash an amount of energy millions of times more powerful than dynamite.

Roosevelt ordered a study. Then in December 1941, Japan attacked the U.S. Naval base at Pearl Harbor, Hawaii. The U.S. joined World War II against Japan and its ally Germany. Soon, Americans were fighting and dying in Europe and Asia. For U.S. leaders, the quest for an atomic bomb took on a new urgency.

World War II began in Europe when German dictator Adolf Hitler attacked Poland in September 1939. Only a month earlier, physicist Albert Einstein had written to U.S. President Franklin D. Roosevelt. Einstein warned that German scientists might be using new advances in physics to engineer a nuclear weapon.

Building such a weapon would involve splitting the nucleus of an atom. That process is called fission. Using the element uranium, fission could cause a chain reaction that would unleash a huge amount of energy. It would be millions of times more powerful than dynamite.

Roosevelt ordered a study. Then in December 1941, Japan attacked the U.S. Naval base at Pearl Harbor, Hawaii. The U.S. immediately joined World War II against Japan and its ally Germany. Soon, Americans were fighting and dying in Europe and Asia. For U.S. leaders, the search for an atomic bomb became urgent.

STR/AFP/Getty Images

North Korean dictator Kim Jong Un (center) inspects a device thought to be a nuclear bomb.

Making the Bomb

“The Manhattan Project was given the highest priority of all U.S. wartime efforts,” says Alex Wellerstein, a historian at Stevens Institute of Technology in New Jersey. About 500,000 people, including thousands of scientists, worked on the project, named for the location of its first headquarters in New York City. Multiple secret test sites and labs were located elsewhere, including Tennessee, Washington State, and New Mexico.  

The technical challenges of making the bomb were immense. “Because they were doing this for the first time, it wasn’t even clear that it could be made to work correctly,” says Wellerstein. And then, he says, “it had to be made small enough to fit inside of an airplane.”

“The Manhattan Project was given the highest priority of all U.S. wartime efforts,” says Alex Wellerstein. Wellerstein is a historian at Stevens Institute of Technology in New Jersey. About 500,000 people worked on the Manhattan Project. That number included thousands of scientists. The project was named for the location of its first headquarters in New York City. A number of secret test sites and labs were located elsewhere. The locations included Tennessee, Washington State, and New Mexico.

The technical challenges of making the bomb were huge. “Because they were doing this for the first time, it wasn’t even clear that it could be made to work correctly,” says Wellerstein. And then, he says, “it had to be made small enough to fit inside of an airplane.”

Many Americans have questioned whether the atomic bomb was worth the devastation it caused.

Finally, in July 1945, the first atomic bomb was detonated at a test site near Alamogordo, New Mexico. The explosion, with the force of 20,000 tons of dynamite, produced a giant mushroom cloud, crowned by a ball of smoke and fire that reached 30,000 feet into the air.

“We knew the world would never be the same,” lead scientist J. Robert Oppenheimer later said. 

Officials were relieved. The bomb worked. Now, what would they do with it?

Finally, in July 1945, the first atomic bomb was set off at a test site near Alamogordo, New Mexico. The explosion had a force of 20,000 tons of dynamite. It produced a giant mushroom cloud, topped by a ball of smoke and fire. The cloud reached 30,000 feet into the air.

“We knew the world would never be the same,” lead scientist J. Robert Oppenheimer later said.

Officials were relieved. The bomb worked. Now, what would they do with it?

Dropping the Bomb on Japan

That grave decision fell to the new president, Harry S. Truman. Truman, previously vice president, had taken office in April 1945, when Roosevelt died suddenly.

Then in May, the Germans surrendered, ending the war in Europe. But the Japanese kept fighting. Truman had to decide whether to risk an invasion of Japan that could claim the lives of hundreds of thousands of Americans—or drop the bomb. Truman would later say it was an easy decision to use the new weapon. 

On August 6, a U.S. warplane dropped an atomic bomb nicknamed “Little Boy” over Hiroshima. The explosion destroyed 5 square miles of the city. Some 80,000 people were killed instantly. Tens of thousands of others died later from radiation sickness.

Three days later, the U.S. dropped another bomb, “Fat Man,” on Nagasaki. It would kill about 80,000 people. 

On August 15, Japanese Emperor Hirohito announced Japan’s surrender. World War II was over.

That serious decision fell to the new president, Harry S. Truman. Truman had been the vice president. He took office in April 1945, when Roosevelt died suddenly.

Then, in May, the Germans surrendered. That ended the war in Europe. But the Japanese kept fighting. Truman had to decide whether to risk an invasion of Japan that could claim the lives of hundreds of thousands of Americans, or drop the bomb instead. Truman would later say it was an easy decision to use the new weapon.

On August 6, a U.S. warplane dropped an atomic bomb nicknamed “Little Boy” over Hiroshima. The explosion destroyed 5 square miles of the city. Some 80,000 people were killed instantly. Tens of thousands of others died later from radiation sickness.

Three days later, the U.S. dropped another bomb, called “Fat Man,” on Nagasaki. It would kill about 80,000 people.

On August 15, Japanese Emperor Hirohito announced Japan’s surrender. World War II was over.

World History Archive/Alamy Stock Photo

A man injured in the blast

The “Arms Race”

Since 1945, many Americans have questioned whether the atomic bomb was worth the devastation it caused. While it ended the war, the bomb gave nations the power to destroy one another as never before.

By 1949, the Soviet Union also had nuclear weapons, leading to an “arms race” with the U.S. That race reached a climax in 1962, when the Soviets placed nuclear missiles in Cuba, 90 miles from Florida. President John F. Kennedy demanded that the missiles be removed. After 13 tense days, the Soviets backed down. It was the closest the world ever came to all-out nuclear war.

Since then, the United Nations (U.N.) and individual countries have worked to limit nuclear arms. That was the goal of the Nuclear Nonproliferation Treaty (1970), signed by 191 countries. Yet today, nine countries possess nuclear weapons (see “The Nuclear Club,” below). Russia (which inherited the Soviet Union’s stockpile) and the U.S. have more than 90 percent of them. 

Experts warn that a conflict between nuclear-armed enemies like Pakistan and India could draw other nations into a wider war. They also worry that a nuclear weapon could be stolen from an unstable government and used by terrorists.

Since 1945, many Americans have questioned whether the atomic bomb was worth the damage it caused. It ended the war. But the bomb also gave nations the power to destroy one another as never before.

By 1949, the Soviet Union also had nuclear weapons. That led to an “arms race” with the U.S. That race reached a climax in 1962, when the Soviets placed nuclear missiles in Cuba, 90 miles from Florida. President John F. Kennedy demanded that the missiles be removed. After 13 tense days, the Soviets backed down. It was the closest the world ever came to all-out nuclear war.

Since then, the United Nations (U.N.) and individual countries have worked to limit nuclear arms. That was the goal of the Nuclear Nonproliferation Treaty. That agreement was signed by 191 countries in 1970. Yet today, nine countries possess nuclear weapons. (See “The Nuclear Club,” below.) Russia inherited the Soviet Union’s stockpile. Today, Russia and the U.S. have more than 90 percent of the world’s nuclear weapons.

Experts warn that a conflict between nuclear-armed enemies like Pakistan and India could draw other nations into a wider war. Experts also worry that a nuclear weapon could be stolen from an unstable government and used by terrorists.

The U.S. and Israel are especially concerned about Iran, which once seemed to be on the path to obtaining nuclear weapons. In 2015, Iran agreed with the U.S. and five other nations to temporarily limit its nuclear program to peaceful purposes. But President Trump doesn’t trust Iran. He has threatened to leave the agreement, made under former President Barack Obama. Critics say that move could cause Iran to restart its weapons program.

And then there’s North Korea, which became a nuclear power a decade ago. Kim Jong Un has tested intercontinental ballistic missiles that may be able to reach some U.S. cities. The threat of a nuclear attack on South Korea is also very real. 

The U.S. and Israel are especially concerned about Iran. That country once seemed to be on the path to getting nuclear weapons. In 2015, Iran agreed with the U.S. and five other nations to temporarily limit its nuclear program to peaceful purposes. But President Trump does not trust Iran. He has threatened to leave the agreement, which was made under former President Barack Obama. Critics say that such a move could cause Iran to restart its weapons program.

North Korea became a nuclear power a decade ago. Kim Jong Un has tested intercontinental ballistic missiles that may be able to reach some U.S. cities. The threat of a nuclear attack on South Korea is also very real.

A World Without Nukes?

Could nuclear arms ever be eliminated? Peace activists have long pursued that goal. But skeptics say no nation will give up its nukes if it knows another has them. 

“We have to be realistic,” says Nikki Haley, the U.S. ambassador to the U.N. “Is there anyone who thinks that North Korea would ban nuclear weapons?”

That thinking hasn’t stopped the International Campaign to Abolish Nuclear Weapons (ICAN), the group awarded the Nobel Peace Prize this month. ICAN knows it won’t be easy to achieve its goal of ridding the world of nuclear arms. But it believes that through negotiations, world leaders can gradually be convinced to destroy all of those weapons. 

Wellerstein also thinks that having the U.S. and North Korea talk—rather than simply threaten each other—is the only way forward. 

“We hope that, away from the cameras, the leaders of these countries understand the dangers,” he says. “Hopefully, this will lead people to search for ways to make the world safer.”

Could we ever completely get rid of nuclear arms? Peace activists have long pursued that goal. But skeptics say that no nation will give up its nukes if it knows another nation has them.

“We have to be realistic,” says Nikki Haley. Haley is the U.S. ambassador to the U.N. “Is there anyone who thinks that North Korea would ban nuclear weapons?”

That thinking has not stopped the International Campaign to Abolish Nuclear Weapons (ICAN). That group was awarded the Nobel Peace Prize this month. ICAN knows it will not be easy to achieve its goal of getting rid of nuclear arms. But it believes that through negotiations, world leaders can gradually be convinced to destroy all of those weapons.

Wellerstein thinks that the U.S. and North Korea should talk rather than threaten each other. He thinks this is the only way to move forward.

“We hope that, away from the cameras, the leaders of these countries understand the dangers,” he says. “Hopefully, this will lead people to search for ways to make the world safer.”

CORE QUESTION: Why might many Americans have questioned the use of the atomic bomb on Japan?

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