Pioneers, WWII

The Atomic Endgame – Hiroshima and Nagasaki

August 6th and 9th, 1945 marked one of the most consequential turning points in global history. The United States dropped two atomic bombs on the Japanese cities of Hiroshima and Nagasaki.

This fateful event concluded the Second World War, igniting a new era of warfare that changed the global political landscape forever.

The Manhattan Project

The Manhattan Project was conceived in 1939, against the backdrop of growing fears that Nazi Germany was also attempting to develop atomic weapons. Einstein’s letter to President Franklin Roosevelt warned him of the potential for nuclear weaponry and the risk of Germany leading this pursuit.

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This sparked the initiation of the project.

The project’s name, “Manhattan,” originated from its initial headquarters at the Manhattan Engineer District of the U.S. Army Corps of Engineers in New York City.

Enrico Fermi, John R. Dunning, and Dana P. Mitchell in front of the cyclotron in the basement of Pupin Hall at Columbia University
Enrico Fermi, John R. Dunning, and Dana P. Mitchell in front of the cyclotron in the basement of Pupin Hall at Columbia University

However, the project grew far beyond the boundaries of Manhattan, spanning multiple locations across the United States and even stretching to Canada and the United Kingdom.

The Manhattan Project was led by General Leslie R. Groves, a senior officer in the United States Army Corps of Engineers. Its scientific division, tasked with the technical aspects of creating the atomic bombs, was directed by physicist J. Robert Oppenheimer.

The project employed some of the most brilliant minds of the era, including Nobel laureates such as Enrico Fermi, Richard Feynman, and Niels Bohr.

General Groves was the CO behind the Manhattan Project.
General Groves was the CO behind the Manhattan Project.

Several large-scale facilities were established to support the project:

  • Los Alamos Laboratory, New Mexico: This was the primary scientific research facility where the bombs were designed.
  • Hanford Site, Washington: This facility produced plutonium-239, a key component of the “Fat Man” bomb.
  • Oak Ridge, Tennessee: The Oak Ridge facility was established to enrich uranium for the “Little Boy” bomb.
  • University of Chicago, Illinois: The first self-sustained nuclear chain reaction was conducted under the university’s football stadium.

It led to several significant scientific and technological advancements.

The first was the successful operation of the world’s first nuclear reactor, Chicago Pile-1, in December 1942. This marked the first self-sustained nuclear chain reaction, a milestone in nuclear physics.

The destruction of Hiroshima and Nagasaki started with the introduction of the first nuclear reactor.
The first ever nuclear reactor.

It also developed two types of atomic bombs: a relatively simple gun-type fission bomb using uranium-235 (codenamed “Little Boy”) and a more complex implosion-type fission bomb using plutonium-239 (codenamed “Fat Man”).

In July 1945, the project reached its climax with the Trinity test in New Mexico, the world’s first detonation of a nuclear weapon.

Testing was successful, and the explosion was equivalent to about 20 kilotons of TNT.

The project also kick-started the nuclear age, leading to the development of nuclear power and setting the stage for the Cold War nuclear arms race.

It raised profound ethical, political, and strategic issues which remain relevant to this day, particularly concerning nuclear proliferation and disarmament.

In many ways, the Manhattan Project represents the intersection of science, technology, and societal impact – showcasing both the incredible power of human intellectual achievement and the devastating potential of that power when used destructively.

The War in the Pacific

The Pacific War began on December 7, 1941, when Japan attacked Pearl Harbor, bringing the United States into the Second World War.

Japan sought to establish what it called the “Greater East Asia Co-Prosperity Sphere,” essentially creating a self-sufficient bloc of Asian nations led by Japan and free from Western influence.

The attack of Pearl Harbour dragged the US into the war.
The attack of Pearl Harbour dragged the US into the war.

The United States and its allies were engaged in a bitter and bloody struggle with Japanese forces across the Pacific.

By 1944, the U.S. had turned the tide of war in its favour, having won several significant battles, including the Battle of Midway and the Guadalcanal Campaign.

However, the closer Allied forces got to Japan, the more ferocious the resistance.

This was evidenced in the Battle of Okinawa from April to June 1945, one of the war’s bloodiest battles, resulting in a high number of casualties on both sides.

The Japanese military demonstrated a willingness to fight to the last man, employing kamikaze tactics and showing no inclination to surrender.

Given the scale of the resistance, Allied leaders feared that a full-scale invasion of the Japanese mainland, planned under Operation Downfall, would result in an enormous number of casualties.

Operation Downfall was the planned invasion of the Japan.
Operation Downfall was the planned invasion of Japan.

Some estimates suggested that there could be up to a million Allied casualties.

There were also fears about the potential loss of civilian life, given the Japanese government’s policy of arming and mobilising civilians.

In this context, President Truman and his advisers saw the atomic bomb, a product of the Manhattan Project, as a potential way to end the war quickly and decisively.

The new weapon promised to have such devastating power that it might force Japan to surrender without the need for an invasion.

After the successful test of the atomic bomb in July 1945 (the Trinity test), the U.S. issued the Potsdam Declaration, calling for Japan’s unconditional surrender and warning of “prompt and utter destruction” if Japan did not surrender.

Japan’s leadership ignored this ultimatum.

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In light of this, Truman authorized the use of atomic bombs against Japan.

The goal was to break the will of the Japanese leadership and force a surrender, thereby ending the war and avoiding a protracted and bloody invasion.

On August 6, 1945, the U.S. dropped an atomic bomb on Hiroshima.

Three days later, on August 9, a second bomb was dropped on Nagasaki.

The explosions after the detonation at Nagasaki and Hiroshima.
The explosions after the detonation at Nagasaki and Hiroshima.

The Little Boy & Fat Man

Little Boy” and “Fat Man” were the code names given to the two atomic bombs developed by the United States as part of the Manhattan Project and used in the bombings of Hiroshima and Nagasaki, respectively, in August 1945.

Little Boy was a gun-type fission bomb, utilizing uranium-235, a rare isotope of uranium.

The design was relatively simple compared to the implosion-type design used in the Fat Man bomb.

The principle behind the Little Boy bomb was to bring two sub-critical pieces of uranium-235 into contact with each other to achieve a supercritical mass, initiating a chain reaction.

This was done by using conventional explosives to shoot a sub-critical piece of uranium-235 (the “bullet”) down a gun barrel into another sub-critical piece (the “target”).

The Little Boy.
The Little Boy.

Little Boy was about 10 feet long, weighed around 9,700 pounds, and had an estimated yield of 15 kilotons of TNT.

When it was detonated over Hiroshima on August 6, 1945, it created a devastating explosion that destroyed a large portion of the city and killed tens of thousands of people instantly, with many more dying in the aftermath.

Fat Man was an implosion-type fission bomb, utilizing plutonium-239. The implosion design was more complex than the gun-type design and required more precise engineering.

In the Fat Man bomb, a sub-critical sphere of plutonium-239 was surrounded by a shell of conventional explosives.

When these conventional explosives were detonated, they compressed the plutonium-239 sphere, making it supercritical and initiating a nuclear chain reaction.

Fat Man was about 10.5 feet long, weighed around 10,300 pounds, and had an estimated yield of 21 kilotons of TNT.

The larger, Fat Man.
The larger, Fat Man.

It was detonated over Nagasaki on August 9, 1945, causing a massive explosion that destroyed a significant part of the city and resulted in the deaths of tens of thousands of people.

Both Little Boy and Fat Man represented significant advances in military technology, harnessing the destructive power of nuclear fission for the first time.

However, they also marked the dawn of the nuclear age, raising profound questions about the ethical implications of nuclear warfare that continue to resonate to this day.

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The B-29

The two Boeing B-29 Superfortress bombers that dropped the atomic bombs on Japan were “Enola Gay” and “Bockscar.”

The Enola Gay was the B-29 bomber that dropped the first atomic bomb, “Little Boy,” on Hiroshima on August 6, 1945. The aircraft was named after Enola Gay Tibbets, the mother of the pilot, Colonel Paul W. Tibbets Jr.

The B-29 was one of the largest aircraft used in World War II and was particularly known for its range and payload capabilities, making it an ideal choice for this mission.

Enola Gay dropped the first nuclear bomb on Hiroshima.
Both of the B-29s are now museum pieces.

The Enola Gay had been extensively modified at the North American Aviation plant in Inglewood, California, to make it capable of carrying the large and heavy atomic bombs.

On the day of the mission, Enola Gay took off from Tinian, a small island in the Pacific, and flew for approximately six hours before reaching Hiroshima.

The bomb was dropped at 8:15 AM local time, and it exploded 43 seconds later with a yield equivalent to 15 kilotons of TNT.

Bockscar was the B-29 that dropped the second atomic bomb, “Fat Man,” on Nagasaki on August 9, 1945. The aircraft was commanded by Major Charles W. Sweeney.

Like Enola Gay, Bockscar was also a specially modified B-29 capable of carrying the atomic bombs.

Bockscar had initially been scheduled to drop a test bomb on August 10, but the mission was moved up to August 9 due to a forecast of poor weather.

On the day of the mission, the primary target was actually Kokura, but visibility over the city was too poor due to smoke from a previous bombing raid on a nearby city.

The Bockscar's nose art.
The Bockscar’s nose art.

After making three unsuccessful passes over Kokura, Sweeney decided to proceed to the secondary target, Nagasaki.

The bomb was dropped at 11:02 AM local time, and it exploded 47 seconds later with a yield equivalent to 21 kilotons of TNT.

Both Enola Gay and Bockscar are now preserved in museums in the United States.

Enola Gay is on display at the Smithsonian’s National Air and Space Museum’s Steven F. Udvar-Hazy Center in Chantilly, Virginia, and Bockscar is on display at the National Museum of the United States Air Force in Dayton, Ohio.

Damage and Casualties to Hiroshima

The bomb detonated approximately 600 meters (2,000 feet) above the city, creating a blast that instantly destroyed nearly every building within a radius of 1.6 kilometres (1 mile).

The heat from the explosion ignited fires that spread over 11.4 square kilometres (4.4 square miles), leading to a massive firestorm that engulfed the city.

The blast wave and intense heat caused severe damage to buildings, infrastructure, and people, with many structures either flattened or severely damaged up to a radius of approximately 4.7 kilometres (2.9 miles).

The landmark Hiroshima Prefectural Industrial Promotion Hall, now known as the Atomic Bomb Dome or the Hiroshima Peace Memorial, was one of the few structures close to the hypocenter that was left standing.

The explosion at Hiroshima, 5 minutes after the weapon detonated.
The explosion at Hiroshima, 5 minutes after the weapon detonated.

The exact number of casualties caused by the Hiroshima bombing is difficult to determine accurately due to the immense scale of the destruction and chaos. However, it’s estimated that by the end of 1945, approximately 140,000 people had died as a direct result of the bombing.

This number includes those who died from the immediate blast and fires, as well as those who succumbed to injuries and radiation sickness in the following weeks and months.

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The victims included both military personnel and civilians, and the dead and injured encompassed a significant portion of Hiroshima’s population, which was about 350,000 at the time of the bombing.

Beyond the immediate blast, heat, and ensuing fires, a significant factor in the death toll was the radiation released by the bomb.

What was left after the explosion. Utterly devastated Hiroshima.
What was left after the explosion. Utterly devastating.

Those within a certain radius of the explosion were exposed to intense radiation, leading to acute symptoms of radiation sickness such as nausea, vomiting, diarrhea, and hair loss. Many of these individuals died within weeks of exposure.

Longer-term, survivors—known as hibakusha—suffered from increased rates of cancer and other health issues likely caused by radiation exposure.

The psychological trauma also had a lasting impact on the survivors and their descendants.

Damage and Casualties to Nagasaki

Unlike Hiroshima’s relatively flat terrain, Nagasaki is situated in a series of narrow valleys surrounded by mountains, which significantly affected the bomb’s impact. The bomb detonated at approximately 500 meters (1,650 feet) above the city.

The initial blast caused severe damage within a radius of approximately 3 kilometres (1.9 miles), much of which was concentrated in the Urakami Valley.

The landscape and relatively hilly terrain of Nagasaki resulted in a somewhat contained blast, but the damage within the blast zone was total.

Before and after photos of Nagasaki.
Before and after photos of Nagasaki.

Ground Zero was the busy industrial and residential Urakami district, home to the Mitsubishi Steel and Arms Works and Nagasaki Medical College.

All buildings within 1.2 miles of ground zero were destroyed, and damage was reported as far as 10,000 feet from ground zero.

Fires caused additional damage, though not to the same extent as the firestorms in Hiroshima due to Nagasaki’s geographical layout.

Estimating the exact number of casualties in Nagasaki is complex due to factors such as intense destruction, immediate chaos, and the ongoing effects of radiation. However, it’s generally agreed that by the end of 1945, between 40,000 and 80,000 people had died as a direct result of the bombing.

This estimate includes those killed instantly by the blast and those who died in the following weeks from injuries and radiation sickness.

The victims encompassed both military personnel and civilians. As with Hiroshima, the dead and injured represented a significant portion of Nagasaki’s population, which was approximately 240,000 at the time of the bombing.

The second attack was justas destructive as Hiroshima.
The second attack was just as destructive as Hiroshima.

Similar to Hiroshima, the inhabitants of Nagasaki were subjected to the harmful effects of ionizing radiation from the bomb. Many of those within a certain radius of the explosion experienced acute symptoms of radiation sickness.

Furthermore, survivors—known as hibakusha—were likely to have increased rates of certain types of cancer and other health problems in the long term.

Today, the Nagasaki Peace Park and the Nagasaki Atomic Bomb Museum stand near the hypocenter of the explosion, serving as reminders of the devastating impact of nuclear warfare.

The destruction of Nagasaki, along with Hiroshima, has significantly shaped global perspectives on nuclear weapons, propelling movements for nuclear disarmament and peaceful conflict resolution.

Double Survivors

“Double Survivors,” also known as “nijū hibakusha” in Japanese, is a term used to refer to the individuals who survived both atomic bombings in Hiroshima on August 6, 1945, and Nagasaki on August 9, 1945.

These individuals experienced firsthand the catastrophic effects of nuclear warfare not once but twice, a testament to both the profound horror of these events and the remarkable resilience of the human spirit.

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Although exact figures are not known, the Japanese government recognized 165 individuals as nijū hibakusha as of 2009.

This number might be higher since not everyone affected came forward due to the stigma associated with being a hibakusha.

One of the most well-known double survivors is Tsutomu Yamaguchi. Yamaguchi was in Hiroshima on a business trip for his employer, Mitsubishi Heavy Industries, when the “Little Boy” bomb was dropped.

He suffered burns and temporary blindness but was able to return to his home in Nagasaki, only to experience the “Fat Man” bomb explosion there three days later.

Despite his injuries and the psychological trauma of surviving two nuclear explosions, Yamaguchi went on to live a long life, passing away at the age of 93 in 2010.

He spent his later years advocating for nuclear disarmament, drawing on his experiences to highlight the devastating human impact of nuclear weapons.

Yamaguchi and other nijū hibakusha represent a unique and deeply tragic aspect of the atomic bombings in Japan.

Their experiences serve as stark reminders of the enormous destructive power of nuclear weapons and the lasting impact they can have on individuals and communities.

Planned Further Attacks

While the bombings of Hiroshima and Nagasaki effectively ended the Second World War, the United States had initially planned for the possibility of further atomic attacks on Japan.

The development and deployment of atomic bombs were part of a broader strategy to compel Japan’s surrender and avoid the need for a costly and protracted invasion of the Japanese home islands.

Memorandum from Groves to Marshall regarding the third bomb, with Marshall's hand-written caveat that the third bomb not be used without express presidential instruction.
Memorandum from Groves to Marshall regarding the third bomb, with Marshall’s hand-written caveat that the third bomb not be used without express presidential instruction.

When President Truman authorized the use of atomic bombs on July 25, 1945, he approved a directive that allowed the military to use additional bombs as they became available.

The directive specified that additional targets would be chosen to cause the greatest psychological impact on Japan and disrupt its capacity to wage war.

The Manhattan Project, which had already produced the “Little Boy” and “Fat Man” bombs, was capable of producing more atomic bombs, though at a limited rate due to the complexity of the process and the scarcity of fissile material.

General Leslie Groves, who was in charge of the Manhattan Project, stated in a report that a third bomb could have been ready for use by August 19, and three more in September 1945.

However, the exact targets for these additional bombs are not explicitly known.

According to various sources, other potential targets could have included the cities of Kokura, Niigata, and Kyoto, though Kyoto was reportedly spared due to its cultural and historical significance.

The dropping of the atomic bombs on Hiroshima and Nagasaki had such a profound impact, causing massive destruction and loss of life, that Japan surrendered before any further bombings were carried out.

On August 15, six days after the bombing of Nagasaki, Emperor Hirohito announced Japan’s surrender, bringing World War II to an end.

Japan’s Surrender

Japan had initially hoped for better terms of surrender through diplomatic intervention by the Soviet Union.

A newpaper reporting on the attacks.
A newspaper reporting on the attacks.

However, this hope was dashed when the Soviets declared war on Japan on August 8, 1945, and launched a massive invasion of Japanese-occupied Manchuria.

Faced with these insurmountable challenges, Emperor Hirohito and his war council had to reconsider their position.

Finally, on August 10, Japan communicated its willingness to surrender to the Allies, with the condition that the status of the Emperor would remain unchanged.

However, the Allies responded with the demand for unconditional surrender.

This demand had initially been stipulated in the Potsdam Declaration, issued by the Allies on July 26, which called for Japan’s unconditional surrender or face “prompt and utter destruction.”

On August 14, after several internal discussions and debates within the Japanese government, Emperor Hirohito broke the deadlock by declaring that the war should be ended.

He cited the devastating power of “a new and most cruel bomb” and the need to “bear the unbearable” to avoid further suffering and loss for the Japanese people.

On August 15, 1945, in a radio broadcast to the Japanese people, the Emperor announced the surrender.

This was a significant event as it was the first time the Japanese public had heard the Emperor’s voice.

The formal surrender document was signed on board the USS Missouri in Tokyo Bay on September 2, 1945, marking the official end of World War II.

Japan’s surrender resulted in a significant shift in the country’s status on the global stage. It led to the Allied occupation of Japan, significant political and social changes, and the creation of a new constitution.

Despite the condition in their initial surrender proposal, Japan’s post-war constitution, enacted in 1947, significantly altered the role of the Emperor, reducing the position to a purely symbolic one without political power.


The nuclear attacks on Hiroshima and Nagasaki forever changed the course of history, bringing an abrupt end to World War II and ushering in the nuclear age.

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The bombings remain a stark reminder of nuclear weapons’ destructive power, influencing international arms control and disarmament debates for decades.

As we remember the immense loss and suffering they caused, we are compelled to question the ethics of nuclear warfare and strive for a world where such devastating weapons are never used again.

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