Fear ignited the first atomic bombs.
August 13, 1942: The U.S. Army Corps of Engineers officially created the Manhattan Engineer District in New York City, marking the official beginning of the top-secret Manhattan Project.
In December 1938, German scientists Otto Hahn and Fritz Strassmann split a uranium atom in a Berlin laboratory. Physicists elsewhere understood immediately what they were looking at: a process that could, in theory, be turned into a weapon of a scale nobody had built before.
Many of the scientists who grasped this fastest had already fled Nazi Germany. They knew exactly what kind of government might get there first.
That fear traveled with them. It reached Albert Einstein and Leo Szilard, who wrote to President Roosevelt in 1939 warning him of the possibility. It reached the Army Corps of Engineers, which issued a general order on Aug. 13, 1942, quietly establishing the Manhattan Engineer District out of an office in New York City. And it built, within three years, one of the largest and most expensive industrial undertakings in American history.
The Race
A month later, on Sept. 17, Army engineer Leslie Groves took command of the project and would run it for the next three years, overseeing everything from the Los Alamos laboratory to the final decision to use the bomb on Japan.
The project’s entire justification rested on a single assumption: Germany was working toward the same weapon, and had a head start. That fear shaped everything that followed, the funding, the urgency, nearly two billion dollars poured into a technology that had never been proven to work outside a laboratory. The project moved forward on the strength of that assumption for years before anyone could confirm or deny it.
As Allied forces advanced across Europe, a covert intelligence unit called the Alsos Mission moved with them. Commanded by Lt. Col. Boris Pash, the team’s job was to find out how close Germany actually was, capturing physicists, seizing lab notebooks, and interrogating scientists before their work could disappear or fall into Soviet hands.
No Stopping Now
By late 1944, Alsos had its answer. Germany’s program, led in part by physicist Werner Heisenberg, had never advanced past the experimental stage. There was no German bomb, and there had never been a real race to lose. In the war’s final weeks, Alsos teams captured Heisenberg and nine other senior German scientists and held them in secret at a country house in England, where their private conversations, including their reactions to hearing that Hiroshima had been bombed, were recorded without their knowledge.
None of that changed course in Washington. The Manhattan Project kept building, and it kept its secret with remarkable discipline. At its peak the project employed more than 130,000 people, most of whom had no idea what they were working on. Compartmentalization was the design itself: know only your own piece, and the shape of the whole thing stays invisible, even to the people building it.
For three years, nothing meaningful about the project reached the public.
The Leak
It reached Moscow instead.
Los Alamos, the weapons laboratory J. Robert Oppenheimer directed, was the most closely guarded site in the entire project. Klaus Fuchs was a German-born physicist who had fled the Nazis, become a British citizen, and earned a security clearance at Los Alamos itself.
Starting in 1942 and continuing through the war’s final years, Fuchs passed detailed atomic secrets to Soviet intelligence, including design information on both the uranium and plutonium bombs. He wasn’t caught until 1949, four years after Hiroshima, when American codebreakers cracked the Soviet cables that named him. Some estimates suggest his information let the Soviet Union test its own bomb a year or two earlier than it otherwise would have.
The country had spent three years hiding its greatest secret from its own machinists, its own construction crews, its own soldiers. It never needed to. The man who gave it away already had the keys.
Hiroshima and Nagasaki
“Little Boy” was dropped on Hiroshima on August 6, 1945. “Fat Man” fell on Nagasaki three days later. Hundreds of thousands of people were killed, including civilians, an estimated 3,000 to 11,000 Japanese American citizens caught in Japan when the war began, and 12 American POWs held in a Hiroshima police station.
The bombings arguably ended World War II. They also proved, decisively and publicly, that the United States had won a race nobody had actually been running against.
Following Germany’s defeat, the captured Nazi physicists, including Werner Heisenberg, were still being held at Farm Hall in England. When they heard the radio broadcasts about Hiroshima, Heisenberg refused to believe it at first. “I don’t believe a word of the whole thing,” he said.