History of nuclear weapons facts for kids

A nuclear fireball lights up the night during a US nuclear test called Upshot-Knothole Badger on April 18, 1953.

A nuclear weapon, also known as an atomic bomb, gets its huge destructive power from splitting atoms (called nuclear fission) or from combining atoms (called fusion).

During World War II, scientists made big discoveries about atoms. In 1941, the United Kingdom started the first nuclear weapons project, code-named Tube Alloys. The United States joined in 1942 with the Manhattan Project, working with the UK and Canada to build a weapon using nuclear fission. In August 1945, the US used nuclear weapons for the only time in war, dropping atomic bombs on Hiroshima and Nagasaki in Japan.

Soon after, the Soviet Union started its own atomic bomb project. Both countries then began developing even more powerful fusion weapons, known as hydrogen bombs. Britain and France also built their own nuclear systems in the 1950s. Since then, the number of countries with nuclear weapons has slowly grown.

How Nuclear Weapons Work

In the early 1900s, scientists learned a lot about atoms. They found that atoms have a tiny, dense center called a nucleus. Scientists like Pierre and Marie Curie discovered that some materials, like uranium ore, gave off a lot of radiation. This made people wonder if atoms held huge amounts of hidden energy.

The idea of an "atom bomb" even appeared in a 1914 novel by H. G. Wells, called The World Set Free. Later, in 1924, Winston Churchill wondered if a bomb "no bigger than an orange" could destroy a whole city block.

In 1933, physicist Leo Szilard had an idea for a nuclear chain reaction using tiny particles called neutrons. He also came up with the term critical mass. This is the smallest amount of material needed to keep a chain reaction going and cause a big explosion. Szilard's ideas were far ahead of his time. He later helped build the first nuclear reactor, Chicago Pile-1, in 1942.

In 1938, scientists Otto Hahn and Fritz Strassmann found that uranium atoms could split when hit by neutrons. Lise Meitner and Otto Robert Frisch explained this as "fission," like a cell splitting into two. This discovery quickly spread around the world.

Scientists soon realized that uranium-235 was the key. When its nucleus absorbs a neutron, it splits, releasing energy and more neutrons. These new neutrons can then split other uranium-235 atoms, creating a chain reaction. This is why uranium-235 is called "fissile." Another type, uranium-238, usually doesn't split this way.

By the start of World War II in 1939, many scientists knew nuclear fission could be a weapon. In August 1939, Albert Einstein wrote a letter to US President Franklin D. Roosevelt. He warned that Germany might be trying to build its own atomic weapons.

Building the First Atomic Bombs

President Roosevelt started the Uranium Committee, but progress was slow at first. After the US entered the war in December 1941, the country decided to put huge resources into a top-secret bomb project.

Britain and Canada had already started the Tube Alloys project. Scientists Rudolf Peierls and Frisch calculated that the critical mass for uranium-235 was much smaller than thought. This meant a bomb could actually be built and delivered. They wrote in 1940 that such a "super-bomb" would create temperatures like the sun and destroy life in a wide area.

A man named Edgar Sengier, who ran a mine in Congo with the best uranium ore, feared the Germans might seize it. In late 1940, he shipped all his uranium to a warehouse in New York.

By mid-1942, it was clear that Britain's wartime economy couldn't handle the massive industrial effort needed for the bomb. In September 1942, General Leslie Groves was chosen to lead the US project, which became known as the Manhattan Project. He quickly bought all 1,250 tons of Sengier's uranium ore. After the US and UK signed the Quebec Agreement in 1943, the British Tube Alloys project joined the Manhattan Project. Canada also provided uranium and plutonium.

The Manhattan Project brought together top scientists, including many who had fled Europe. They worked with American industry to build fission bombs before Germany could. The US invested a huge amount of money, making it the second-largest industrial project ever. Secret laboratories were set up, with the main one at Los Alamos.

To make a fission bomb, you need enough fissile material to start a chain reaction, called a critical mass. Scientists developed ways to separate uranium-235 from uranium-238. A huge secret factory was built at Oak Ridge, Tennessee, to produce this rare uranium-235. Tens of thousands of people worked there, often without knowing what they were making.

Another fissile material is plutonium-239. Uranium-238 can turn into plutonium-239 when it absorbs a neutron. After the first controlled nuclear chain reaction was achieved in Chicago, massive reactors were built at the Hanford Site to make plutonium from uranium-238.

The simplest atomic bomb design is a gun-type fission weapon. This shoots one piece of fissile material into another, creating a critical mass and a huge explosion. The first bombs planned were the "Little Boy" (uranium) and "Thin Man" (plutonium) gun-type bombs, and the "Fat Man" plutonium implosion bomb.

However, in 1944, scientists found that the plutonium from the Hanford reactors had too many impurities. This meant a gun-type plutonium bomb wouldn't work well; it would "fizzle" and have a much smaller explosion. So, they focused on the "Fat Man" design. This bomb used chemical explosives to squeeze a sphere of plutonium, making it dense enough to become critical and explode.

After D-Day, a team of scientists followed Allied troops into Europe to check on Germany's nuclear program. They found that Germany had not invested much in its project and was far from building a bomb. Japan's efforts were also very limited.

The Decision to Use the Bomb

After President Roosevelt died, Harry S. Truman became president in April 1945. Germany surrendered in May 1945, but the Manhattan Project was still months away from a working bomb.

Because the plutonium bomb was so complex, a test was needed. On July 16, 1945, the first nuclear test, code-named "Trinity," took place in the New Mexico desert. The device, called "the gadget," was a plutonium implosion bomb. It released energy equal to 22,000 tons of TNT, far more powerful than any weapon ever used.

President Truman was told about the test's success at the Potsdam Conference. He then issued the Potsdam Declaration, telling Japan to surrender or face "complete and utter destruction." Nuclear weapons were not directly mentioned.

Truman decided to use the bombs on Japanese cities. The US and UK had agreed that nuclear weapons would not be used without both countries' consent. Truman hoped the bombs would force Japan to surrender quickly and avoid a long, costly invasion. He also wanted to end the war before the Soviets could join the fight in the Pacific.

On August 6, 1945, a uranium bomb, "Little Boy," exploded over Hiroshima, Japan. Three days later, a plutonium bomb, "Fat Man," exploded over Nagasaki. These are the only times nuclear weapons have been used in combat. The bombings killed at least 100,000 Japanese civilians and military personnel immediately. Many more died later from radiation sickness and related illnesses. On August 15, Emperor Hirohito announced Japan's surrender.

The Soviet Atomic Bomb Project

The Soviet Union was not invited to share the new weapons technology. However, Soviet spies, including physicist Klaus Fuchs, had been sending information from the Manhattan Project. So, when Truman told Joseph Stalin about the "powerful new weapon" at the Potsdam conference, Stalin was not surprised. He was, however, very upset about the American nuclear monopoly. The Soviets quickly started their own atomic program.

The Soviet program, led by physicist Yuli Khariton, worked to copy the American effort. On August 29, 1949, the USSR successfully tested its first fission bomb, called "Joe-1" by the US. The US detected radioactive traces from the test and announced it to the world. This marked the start of the nuclear arms race.

The First Hydrogen Bombs

The idea of using a fission bomb to start a nuclear fusion process (a "Super" bomb or hydrogen bomb) came up in 1941. At first, scientists thought it would be easy, but building the regular atomic bomb took all their focus. Only Edward Teller kept working on the "Super" bomb idea.

When the Soviet Union tested its atomic bomb in 1949, it was earlier than the Americans expected. This led to a big debate in the US about whether to build the much more powerful Super bomb. Many scientists at Los Alamos did not want to create a weapon thousands of times stronger than the first atomic bombs. They argued it could only be used against large groups of people, which they saw as wrong.

However, supporters like Teller argued that such a weapon was bound to be developed, and the US needed it for protection. President Truman made the final decision. On January 31, 1950, he announced a crash program to develop the hydrogen bomb.

A key breakthrough came from mathematician Stanislaw Ulam. He suggested that the fission bomb and the fusion fuel could be in separate parts of the bomb. The radiation from the fission bomb could then squeeze the fusion material before igniting it. This became the basis for the Teller-Ulam design.

The US tested its first fusion bomb, code-named "Mike," on November 1, 1952. It was on Elugelab Island in the Marshall Islands. This device was huge and couldn't be dropped from a plane. Its explosion was equal to 10.4 million tons of TNT, over 450 times more powerful than the Nagasaki bomb. It completely destroyed Elugelab Island.

Less than a year later, on August 12, 1953, the Soviet Union exploded its first thermonuclear device, called "Joe-4" by the West. Unlike Mike, this Soviet device was small enough to be delivered by a plane. This worried the US.

On March 1, 1954, the US tested its first practical thermonuclear weapon, called "Shrimp" (part of the Castle Bravo test), at Bikini Atoll. This bomb yielded 15 million tons of TNT, much more than expected. It caused the worst radiological disaster in US history. A cloud of radioactive fallout spread over a huge area, exposing many people to radiation. The crew of a Japanese fishing boat, the Lucky Dragon 5, got sick from the fallout, and one crew member died. This incident made people around the world very concerned about radiation.

The immense power of hydrogen bombs made people realize that a nuclear war could lead to worldwide destruction. This fear became a major part of the Cold War.

Deterrence and Brinkmanship

Throughout the 1950s and early 1960s, the US and the USSR tried to stop each other from gaining nuclear superiority. This had a huge impact on politics and culture during the Cold War.

Early atomic bombs were large and needed special planes to carry them. The first hydrogen bombs were also huge. This meant only one bomb could be carried per plane. To improve their nuclear weapons, the US started a nuclear testing program.

Starting in 1951, the Nevada Test Site became the main place for US nuclear tests. The Soviet Union used the Semipalatinsk Test Site. These tests were used to check if new weapons worked and to see how they behaved. Most early tests were done in the atmosphere or underwater. Testing showed a country's strength, but it also released nuclear fallout into the air, causing health concerns.

Many scientists and leaders called for a ban on nuclear testing. In 1958, the US, USSR, and UK agreed to stop testing temporarily. But in 1961, the Soviet Union broke the agreement, and both countries started testing frequently again.

In October 1961, the Soviet Union tested the largest nuclear weapon ever, the "Tsar Bomba." It had a yield of about 50 million tons of TNT. It was too big for military use, but it was a show of power. In 1963, many countries signed the Limited Test Ban Treaty, agreeing not to test nuclear weapons in the atmosphere, underwater, or in space. Underground tests were still allowed.

Weapons became more powerful and smaller. Smaller bombs meant planes could carry more, and they could be put on new rockets. The US rocket program got a big boost from German scientists who had worked on Nazi rockets during WWII.

Nuclear Strategy and the Cold War

Early nuclear rockets had short ranges, meaning they could only be used in specific military situations. To threaten an entire country, long-range bombers were needed. The US created the Strategic Air Command (SAC) to keep nuclear-armed planes in the air 24 hours a day, ready to attack.

The terrible threat of nuclear war led to a new way of thinking about military strategy. President Dwight D. Eisenhower's "massive retaliation" policy warned the USSR that if they attacked Western Europe, the US would use nuclear weapons against them.

As both the US and USSR got nuclear weapons, this policy changed. If one country attacked, the other could strike back, leading to both countries being destroyed. This idea was called Mutually Assured Destruction (MAD).

MAD meant that starting a nuclear war would destroy the attacker too, so no logical country would strike first. The goal was to make sure the enemy could never destroy your ability to strike back. This led to both the US and USSR building thousands of nuclear weapons, far more than needed to destroy each other. This strategy was made fun of in the 1964 movie Dr. Strangelove.

MAD also led to the development of early warning systems. Since rocket attacks could happen in minutes, computers were needed to detect attacks and direct quick responses. The US built SAGE, a system to track enemy bombers using radar. It was one of the first computer systems to work in real-time.

The Anti-Nuclear Movement

The atomic bombings of Hiroshima and Nagasaki, and later nuclear tests, made people around the world very worried. The "Little Boy" bomb on Hiroshima destroyed nearly 50,000 buildings and killed about 75,000 people.

In 1946, the US conducted nuclear tests called Operation Crossroads at Bikini Atoll in the Pacific. The local residents were forced to leave their homes.

In 1954, a hydrogen bomb test in the Pacific contaminated a Japanese fishing boat, the Lucky Dragon. One fisherman died. This incident sparked the anti-nuclear weapons movement in many countries. People felt the atomic bomb showed society was going in a very bad direction.

In Japan, millions of people signed petitions calling for bans on nuclear weapons. In 1955, Bertrand Russell and Albert Einstein issued the Russell–Einstein Manifesto, warning about the dangers of nuclear weapons and urging world leaders to find peaceful solutions.

In the UK, the first Aldermaston March took place in 1958. Thousands of people marched to protest nuclear weapons. In 1961, about 50,000 women marched in 60 US cities against nuclear weapons. This was the largest national women's peace protest of the 20th century.

Scientists also played a role. In 1958, Linus Pauling and his wife collected over 11,000 signatures from scientists asking for an end to nuclear testing. Research in 1961 showed that above-ground nuclear testing caused health risks from radioactive fallout in milk. This public pressure led to the Partial Test Ban Treaty in 1963, which stopped most above-ground nuclear tests.

The Cuban Missile Crisis

By the 1960s, both the United States and the Soviet Union had developed intercontinental ballistic missiles (ICBMs). These could be launched from far away and hit targets anywhere in the world. They also had submarine-launched ballistic missiles (SLBMs), which could be launched from submarines close to targets without warning. This made defending against nuclear attacks almost impossible.

The danger of nuclear war was very high. Leaders would often act very tough, making people fear that their generation might be the last. Civil defense programs, like building fallout shelters, did little to calm these fears.

The most dangerous moment came in 1962. A US spy plane photographed sites for medium-range ballistic missiles being built in Cuba, very close to the US coast. This started the Cuban Missile Crisis. US President John F. Kennedy announced that the Soviet Union was planning to put nuclear missiles on the island, which was controlled by Fidel Castro. Kennedy announced a naval blockade around Cuba and warned that the military was ready for anything. These missiles could quickly destroy many major American cities.

The leaders of the two superpowers were on the edge of a third world war. Soviet leader Nikita Khrushchev offered to remove the missiles if Kennedy promised not to invade Cuba. Khrushchev warned about the danger of pulling too hard on the "knot of war."

A day later, the Soviets also demanded that the US remove its missiles from Turkey. A US spy plane was shot down over Cuba. Kennedy publicly accepted the first deal and secretly agreed to the second. On October 28, the Soviet ships turned back, and Khrushchev announced the missiles would be removed from Cuba.

The Cuban Missile Crisis was the closest the US and USSR ever came to nuclear war. It was avoided by last-minute agreements. This crisis led to the creation of the first hotline, a direct phone link between the two superpowers, to help them talk more easily during future crises.

After this close call, both countries worked to reduce nuclear tensions. The Partial Test Ban Treaty in 1963 was a result, stopping atmospheric, underwater, and space nuclear tests. Underground testing continued, but the risk of worldwide fallout was reduced.

There have been at least four major false alarms that almost led to nuclear attacks, including computer errors and a research rocket being mistaken for a missile.

New Countries Get Nuclear Weapons

In the 1950s and 1960s, three more countries joined the "nuclear club."

The United Kingdom had helped with the Manhattan Project. But after the war, the US passed a law that stopped sharing nuclear information. So, Britain decided it needed its own bomb. They successfully tested an atomic bomb on October 3, 1952. Later, they developed missiles and bought US designs for submarine missiles, but they keep full control over their use.

France had done nuclear research before WWII. After the war, they started a civilian nuclear program that produced plutonium. In 1956, France secretly began a military nuclear program. In 1960, they successfully tested a bomb. Since then, France has kept its own nuclear deterrent separate from NATO.

In 1951, China and the Soviet Union agreed that China would supply uranium ore for technical help with nuclear weapons. China started a research program, and the Soviets provided equipment. Even when relations worsened and the Soviets stopped helping, China made fast progress. China got nuclear weapons in 1964, becoming the fifth country to have them. They tested their first atomic bomb on October 16, 1964. China has a policy of "no first use," meaning they promise not to use nuclear weapons first.

The Cold War and Beyond

After World War II, the fear of global destruction kept countries from using atomic bombs again. This fear was central to the Cold War strategy of Mutually Assured Destruction (MAD). This led to a huge increase in nuclear weapons, as each side wanted to make sure it could destroy the other.

Early ways to deliver bombs were bombers. Later, ballistic missiles were developed by both the US and the Soviet Union, based on German WWII designs. These missiles were used to launch satellites and start the Space Race, but their main purpose was to carry nuclear weapons anywhere in the world. On January 27, 1967, over 60 nations signed the Outer Space Treaty, banning nuclear weapons in space.

There have been many potential nuclear disasters. US nuclear weapons have been lost in air accidents, though most were recovered. The Soviet Union was less open about such incidents, but it's believed they lost many nuclear devices, mostly in submarine accidents.

The end of the Cold War in 1991 reduced global fears of nuclear war. In 1992, Russian President Boris Yeltsin announced that Russia would stop targeting US cities with nuclear weapons.

New Nuclear Powers

The "second nuclear age" refers to nuclear weapons spreading to more countries, often for reasons other than the US-Soviet rivalry.

India started a nuclear program early. After a war with China in 1962, they sped it up. India's first atomic test was in 1974.

After a war in 1971, Pakistan also started nuclear weapons research. India tested more devices in 1998, and Pakistan successfully tested its own fission devices that same year. This raised worries that they might use nuclear weapons against each other.

All former Soviet countries with nuclear weapons (Belarus, Ukraine, and Kazakhstan) transferred their warheads to Russia by 1996.

South Africa had a program to develop uranium-based nuclear weapons but later dismantled it in the 1990s.

Israel is widely believed to have hundreds of nuclear warheads, but they have never officially confirmed or denied it.

In 2004, Dr. A. Q. Khan of Pakistan confessed to being a key part of an international network that spread nuclear materials and knowledge to countries like Libya, Iran, and North Korea.

North Korea announced in 2003 that it had nuclear explosives. They conducted their first claimed test on October 9, 2006, and have continued testing since then, despite international objections.

Images for kids

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  In nuclear fission, an atom's center (nucleus) splits into two new atoms. This releases energy and new particles, which can keep the process going.

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  Leo Szilard, pictured around 1960, had many important ideas, including the nuclear chain reaction.

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  Major General Leslie Groves and Robert Oppenheimer at the Trinity test site in 1945.

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  Physicist J. Robert Oppenheimer led the scientific work at Los Alamos.

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  This shows how much uranium-235 (red) is needed for bombs compared to its natural amount (blue). Separating it is very hard and expensive.

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  An electromagnetic plant at Oak Ridge, Tennessee, used to separate uranium-235.

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  The two fission bomb assembly methods.

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  The atomic bombings of Hiroshima and Nagasaki killed many Japanese people and destroyed factories and military bases.

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  The Bockscar B-29 that delivered the Fat Man bomb, and a post-war nuclear weapon made to look like the Fat Man bomb.

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  Hungarian physicist Edward Teller worked for years to figure out how to make a fusion bomb.

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  The "Mike" test in 1952 started the age of fusion weapons.

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  A November 1951 nuclear test at the Nevada Test Site. Troops were 6 miles from the blast.

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  Nuclear-armed rockets, like the MGR-1 Honest John, changed how nuclear war was thought about.

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  Long-range bomber aircraft, like the B-52 Stratofortress, could carry many strategic nuclear weapons.

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  A SSM-N-8 Regulus missile launched from the submarine USS Halibut.

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  Early warning systems meant nuclear attacks would be managed from control rooms, not battlefields.

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  Women Strike for Peace during the Cuban Missile Crisis.

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  U-2 spy plane photos showed the Soviet Union was putting nuclear missiles on Cuba in 1962, starting the Cuban Missile Crisis.

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  Submarine-launched ballistic missiles with multiple warheads made it very hard to defend against nuclear attacks.

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  ICBMs, like the American Minuteman missile, could deliver nuclear weapons thousands of miles away.

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  On December 12, 1982, 30,000 women held hands around the RAF Greenham Common base to protest against US cruise missiles being placed there.

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  Countries with large nuclear stockpiles (dark blue), smaller global stockpiles (medium blue), and small regional stockpiles (light blue).

See also

In Spanish: Historia de las armas nucleares para niños