German physicist Otto Hahn discovers that uranium atoms split apart and release energy when bombarded with radiation from unstable elements.

Physicist Lise Meitner reasons out the principle of nuclear fission and calculates that uranium could be the core of a devastating super-bomb.

Hungarian physicists bring Albert Einstein to write letters warning President Roosevelt that Germany may be secretly building a uranium weapon.

President Roosevelt establishes a joint science-military Uranium Committee to investigate the requirements for building an atomic bomb.

Japan launches a surprise attack on the US military base at Pearl Harbor, drawing America into World War II.

The US War Department appoints Colonel Leslie Groves to oversee the atomic bomb program, now code-named the Manhattan Project.

General Groves chooses Robert Oppenheimer to lead the scientific effort, overruling widespread objections about his Communist sympathies and poor health.

Enrico Fermi's team achieves the world's first sustained nuclear chain reaction inside a reactor built beneath a University of Chicago squash court.

Norwegian commandos from Operation Gunnerside break into the Vemork power plant and destroy the heavy water production machines used by the German bomb program.

Oppenheimer requests British scientists to help at Los Alamos, and Soviet spy Klaus Fuchs is included among those sent.

Allied forces sweep through Germany, capture leading nuclear scientists, and discover Heisenberg's atomic reactor hidden in a cave, primitive and unfinished.

Scientists detonate the world's first atomic bomb at the Trinity test site in the New Mexico desert, creating a blinding flash and mushroom cloud.

The B-29 Enola Gay drops the uranium bomb called Little Boy on Hiroshima, instantly destroying most of the city and killing tens of thousands.

Emperor Hirohito overrules his military command and orders Japan to surrender, bringing World War II to an end.

The Soviet Union secretly detonates its first atomic bomb, shocking American intelligence agencies that had not expected success for several more years.

The discovery that uranium atoms could be split apart set off a desperate race between the Allies and Nazi Germany to build a super-weapon that could decide the outcome of World War II. The United States organized the massive Manhattan Project under General Leslie Groves and scientist Robert Oppenheimer, pooling resources with Britain to design and build a working atomic device. Key breakthroughs like Fermi's first nuclear chain reaction, combined with Norwegian sabotage of Germany's heavy water supply, kept America ahead in the race. By mid-1945, Allied forces had swept through Germany and found the Nazi bomb program hopelessly unfinished, while the Americans were preparing their own weapon for use in the Pacific. The Trinity test proved the bomb worked, and two atomic weapons dropped on Japanese cities forced an unprecedented imperial surrender and ended the war. The Soviet Union's surprise atomic test just four years later confirmed that the race had not ended with the war but had only entered a new and more dangerous phase.

The race to build and drop the world's first atomic bomb.

Harry Gold agrees to smuggle industrial secrets to Soviet agents as a favor to a Communist acquaintance who found him a job.

Norwegian resistance fighter Knut Haukelid escapes to Britain and is recruited to help sabotage Germany's heavy water operation in Norway.

The British train Norwegian recruits in lock-picking, explosives, and sabotage at a program German spies nickname International Gangster School.

British commandos arrive in Norway aboard silent wooden gliders, but both aircraft crash, and the surviving men are captured and executed by the Nazis.

Oppenheimer and Groves visit a remote canyon plateau in New Mexico and choose it as the site for the central Manhattan Project laboratory.

Princeton physics graduate student Richard Feynman learns the project is building an atomic weapon and immediately signs on, moving to Los Alamos.

Knut Haukelid sneaks aboard the Hydro ferry at night, places timed explosives in the bow, and escapes before the charges sink the vessel and its cargo of heavy water.

Harry Gold meets Klaus Fuchs for the first time in New York City using a prearranged recognition signal involving gloves and a tennis ball.

Harvard prodigy Ted Hall, eighteen years old and newly graduated, is recruited to join the Manhattan Project team at Los Alamos.

One of the US Army Air Force's best combat pilots, Paul Tibbets, is secretly assigned to develop the method for dropping an atomic bomb from a B-29.

George Kistiakowsky's team surrounds a metal plutonium core with precisely arranged explosive charges and successfully tests whether the implosion concept will work.

Allied forces march into Germany and the Nazi government collapses, ending the war in Europe.

Uranium components for the bomb are loaded onto the USS Indianapolis and transported under guard to the Pacific island of Tinian.

A B-29 commanded by Paul Sweeney drops the plutonium bomb Fat Man on Nagasaki, killing forty thousand people instantly and wounding tens of thousands more.

Oppenheimer resigns from Los Alamos and travels to Washington to warn that a world full of nuclear weapons will endanger all of humanity.

Behind the headline race to build an atomic weapon lay a parallel world of espionage, commando raids, and individual acts of courage and betrayal that quietly determined who would win. Harry Gold was drawn into Soviet spying years before the bomb existed, while Norwegian fighters like Knut Haukelid launched two daring operations to cripple Germany's heavy water supply and ultimately sink the shipment meant to save the Nazi bomb program. At Los Alamos, brilliant young scientists like Richard Feynman and Ted Hall joined the project and made vital contributions to solving its most difficult engineering problems. As the bomb neared completion, specialized crews were secretly trained, materials transported across the Pacific, and the weapon assembled on a remote island in preparation for use against Japan. Two atomic bombs dropped within days of each other shattered Japan's will to fight, and in the aftermath Oppenheimer stepped back from Los Alamos to wage a futile campaign against the arms race he had helped to start.

The spies, saboteurs, and scientists who shaped the bomb from the shadows.

Soviet physicist Georgi Flerov notices that American nuclear research journals have suddenly gone silent and warns his government that a secret bomb program must be underway.

The Soviet Union launches the secret intelligence operation code-named Enormoz, dedicated entirely to stealing American atomic bomb plans.

British Prime Minister Churchill and President Roosevelt agree to combine their scientific resources and build the atomic bomb together inside the United States.

Literature professor Haakon Chevalier privately asks Oppenheimer at a dinner party to pass atomic secrets to the Soviets; Oppenheimer refuses, calling it treason.

Ted Hall concludes that the United States should not be the only nuclear power and makes contact with a Soviet agent in New York to share bomb information.

OSS spy Moe Berg attends Werner Heisenberg's lecture in Switzerland, listens carefully, and decides the German bomb program is nowhere near completion.

President Roosevelt dies in office, and Vice President Harry Truman is informed for the first time about the existence of the Manhattan Project.

The night before the Trinity test, Oppenheimer climbs the hundred-foot tower alone to give the bomb a final personal inspection.

After cheering and embracing at the Trinity blast, the scientists fall into stunned silence as they absorb the destructive power they have created.

At Farm Hall in England, German physicist Otto Hahn is devastated with guilt when he learns that his uranium fission discovery led to the Hiroshima attack.

Soviet courier Lona Cohen tucks Ted Hall's written bomb descriptions into a tissue box and talks her way past FBI agents searching passengers at a New Mexico train station.

Oppenheimer meets President Truman in Washington to plead for nuclear disarmament; Truman privately decides he never wants to see the scientist again.

After weeks of sustained questioning by British investigators, Klaus Fuchs finally breaks down and confesses to passing atomic bomb secrets to the Soviet Union.

FBI agents discover a marked map of New Mexico hidden inside a book at Harry Gold's home, and Gold confesses to being a Soviet spy.

Oppenheimer's security clearance is revoked by the US government, permanently ending his ability to advise on the nuclear weapons he helped create.

The atomic bomb's creation was shaped less by grand strategy than by a series of pivotal private choices and startling revelations that quietly altered the course of events. The Soviets recognized they could not build a bomb from scratch and launched a bold espionage campaign, while key figures like Oppenheimer refused to betray their country even when approached by trusted colleagues asking them to spy. Young scientists like Ted Hall made the agonizing personal decision to share bomb secrets with the Soviets, convinced that a nuclear monopoly was more dangerous than a standoff between two armed powers. As the Trinity test approached, the moral weight of the weapon pressed down on its creators, and the bombings of Japan forced every participant to confront what they had unleashed. In the years that followed, the unmasking of Soviet spies and the punishment of Oppenheimer himself—the one man who had most loudly warned the world—revealed the bitter contradictions at the heart of the nuclear age.