A close view of a man smoking a cigarette with a hat.

Oppenheimer: The secrets he protected and the suspicions that followed him

In a race against time and the enemy, J. Robert Oppenheimer helped lead the U.S. effort to build the atomic bomb. But he was almost bounced from the Manhattan Project entirely—why?

J. Robert Oppenheimer, often called the 'father of the atomic bomb,' was almost removed from the Manhattan Project after he fell under suspicion from a military intelligence officer at the Los Alamos Laboratory. 
Photograph By Alfred Eisenstaedt/Pix Inc./Time & Life Pictures

Just by virtue of what they are, secrets are hard to keep. So how do you guard World War II’s topmost secret? That is, the United States’ effort to build the atomic bomb. If word got out, if the Nazis caught on to what was being created, the future of democracy was threatened forever. And if the Nazis beat them to it, they could win World War II.

It all started in 1939, when several prominent scientists, including Albert Einstein, expressed concerns that Nazi Germany might be developing atomic weapons. As a result, the United States government established a highly classified project to pursue their own development of atomic weapons. Initial research was conducted at Columbia University in New York City—giving the mission the code name “Manhattan Project.”

To ensure ultimate secrecy, the Manhattan Project was divided into remote sites across the United States. Eventually, more than 130,000 people were involved in research and development, with three primary locations: Oak Ridge, Tennessee, which focused on uranium enrichment; Hanford, Washington, where plutonium production facilities were constructed; and Los Alamos, New Mexico, where the bulk of the research and weapon design took place. Only a select few knew the full scope and purpose of their work—a key to keeping the project undercover.

One of these leaders was theoretical physicist J. Robert Oppenheimer, Los Alamos’ director. But things weren’t that simple, because the 39-year-old Oppenheimer was under suspicion himself.

(Did the U.S. plan to drop more than two atomic bombs on Japan?)

Suspicious

When Oppenheimer arrived in New Mexico in April 1943 to take charge of the new government lab at Los Alamos, he became critical to the top-secret Manhattan Project. But he did not yet have a security clearance—he was suspected by the FBI and G-2, the Army’s intelligence agency, of being linked to a spy ring run by America’s Soviet allies. A G-2 officer at Los Alamos accused him of “playing a key part in the attempts of the Soviet Union to secure, by espionage, highly secret information which is vital to the security of the United States.”

The accusations stemmed from the fact that several people close to Oppenheimer were past or present members of the Communist Party. Oppenheimer denied joining that party, but while teaching at the University of California, he had supported causes that brought him into contact with Communists or communist sympathizers, including members of the Abraham Lincoln Brigade, who defied U.S. Neutrality Acts by fighting in Spain against Francisco Franco, the dictator backed by Hitler and Mussolini. Oppenheimer did, indeed, share with those fighters a hatred for fascism and helped Jewish relatives and Jewish scientists in Germany flee the Nazi regime.

Moving forward

Oppenheimer’s job was saved by an officer for whom security was of utmost concern—Brig. Gen. Leslie Groves, director of the Manhattan Project. He believed Oppenheimer was uniquely qualified to overcome the challenges of building an atomic bomb by managing other brilliant scientists, whose egos were easily bruised. One of those temperamental scientists, Edward Teller, explained why Oppenheimer was so well suited for the job: “He knew how to organize, cajole, humor, soothe feelings, how to lead powerfully without seeming to do so … Los Alamos’ amazing success grew out of the brilliance, enthusiasm, and charisma with which Oppenheimer led it.”

(Chien-Shiung Wu changed the laws of physics through her work on the Manhattan Project.)

Groves trusted in the judgement of his own security officer at Los Alamos, Capt. John Lansdale, who concluded Oppenheimer was not a communist, which Lansdale defined as someone loyal to the Soviet Union rather than United States.

Utmost secrecy

Reprieved by Groves, Oppenheimer got to work, taking on the monumental task of unleashing atomic energy. The project proved so complex that the U.S. did not have nuclear weapons at its disposal before Germany was defeated in May 1945—which hadn’t had the chance to develop its own nuclear capability thanks to devastating strategic bombing and lack of scientific and industrial capacity.

But Oppenheimer’s scientists at Los Alamos had received enough fuel from Oak Ridge and Hanford by then to produce bombs of two types: one fueled by uranium-235 and the other by plutonium-239. The bombs were secretly tested in July 1945 at a proving ground designated the Trinity Site, in the remote New Mexico desert: A ball of fire shot up into the sky, surrounded by an enormous mushroom cloud some 40,000 across.

The nuclear age had begun—yet still under wraps.

Even though hundreds of scientists and support crew had converged on the New Mexico desert virtually overnight and the blast shook buildings as far away as El Paso, Texas, the War Department did not let the word get out. The state police reported it was an accidental explosion at an Army camp. One man was traveling across New Mexico by train when he saw the sky light up. He informed a Chicago newspaper, saying he thought he had seen a giant meteor, and the reporter filed a brief article. The next day, the FBI visited the publisher’s office and demanded she forget the story, and it never appeared.

End of a secret

President Harry S. Truman was preparing to meet with Soviet leader Joseph Stalin and British Prime Minister Winston Churchill in July 1945 at Potsdam, in Allied-occupied Germany, to discuss postwar peace when he learned about the successful test at the Trinity Site. He then informed the Soviet leader about the big secret. In fact, Stalin already knew about the bomb and had a Soviet nuclear weapons program under way, aided by disclosures from spies at Los Alamos who thus far had eluded detection. 

The stage was set for the war’s shattering conclusion when the Potsdam Declaration was issued on July 26, 1945, calling on Japan to surrender unconditionally or face “prompt and utter destruction,” Unwilling to yield unless Emperor Hirohito was allowed to remain in power, a condition Truman had rejected, Japan dismissed the declaration.

Two binding atomic blasts finally impelled Hirohito to surrender—the first unleashed on August 6, 1945, by a uranium bomb that devastated Hiroshima; and the second triggered three days later by a plutonium bomb that shattered Nagasaki. More than 150,000 people were killed in the attacks, and thousands more were contaminated by radioactive fallout and died later as a result.

The world finally learned about the atomic bomb, and there was no turning back.

Portions of this work have previously appeared in World War II: The Spies and Secret Missions That Won the War by Neil Kagan and Stephen G. Hyslop. Copyright © 2017 National Geographic Partners LLC
To learn more, check out World War II: The Spies and Secret Missions That Won the War. Available wherever books and magazines are sold.

Read This Next

Omega-3s are more critical for your health than we thought
New museum reckons with Charleston’s role in the slave trade
How Barbie’s signature pink took over the world

Go Further

Subscriber Exclusive Content

Why are people so dang obsessed with Mars?

How viruses shape our world

The era of greyhound racing in the U.S. is coming to an end

See how people have imagined life on Mars through history

See how NASA’s new Mars rover will explore the red planet

Why are people so dang obsessed with Mars?

How viruses shape our world

The era of greyhound racing in the U.S. is coming to an end

See how people have imagined life on Mars through history

See how NASA’s new Mars rover will explore the red planet

Why are people so dang obsessed with Mars?

How viruses shape our world

The era of greyhound racing in the U.S. is coming to an end

See how people have imagined life on Mars through history

See how NASA’s new Mars rover will explore the red planet