When people think about the atomic bomb, they usually just picture Cillian Murphy in a wide-brimmed hat. Or maybe they think of Albert Einstein scrawling equations on a blackboard. But honestly? That’s like saying one guy built the entire internet. The reality of who was involved in the Manhattan Project is way more chaotic, massive, and honestly, a bit terrifying when you look at the scale of it.
It wasn't just a few geniuses in a basement. It was a secret empire.
At its peak, this project employed about 130,000 people. To put that in perspective, that’s more people than live in many mid-sized cities today. And most of them had absolutely no clue what they were actually making. They were just turning dials, shifting chemicals, or typing memos in cities that didn't even exist on maps a year prior. It was the ultimate "need to know" basis, and turns out, almost nobody needed to know.
The Big Names Everyone Knows (And Why They Mattered)
You can't talk about the project without J. Robert Oppenheimer. He was the "father of the atomic bomb," sure, but he was more like a high-stakes project manager who happened to be a theoretical physics prodigy. General Leslie Groves, the guy who oversaw the construction of the Pentagon, was the one who actually ran the show. Groves was a blunt, career military man who basically forced the scientists to work under a rigid structure they hated.
Then you had the "Martians." That’s what they called the Hungarian refugees like Leo Szilard and Eugene Wigner because they were so unnervingly brilliant. Szilard was actually the one who first conceived of the nuclear chain reaction while waiting for a traffic light in London. He was the one who nudged Einstein to write that famous letter to President Roosevelt.
And then there’s Enrico Fermi.
Fermi was a beast. He built the first nuclear reactor, Chicago Pile-1, under a football stadium. Literally. They used a squash court at the University of Chicago. There were no cooling systems. No radiation shielding. Just a bunch of guys stacking graphite bricks and hoping they didn't melt the city. It worked.
The "Calutron Girls" and the Unsung Workforce
This is where the story of who was involved in the Manhattan Project gets really interesting. While the physicists were arguing about isotopes in Los Alamos, thousands of young women in Oak Ridge, Tennessee, were doing the heavy lifting.
They were called the Calutron Girls.
Most of them were fresh out of high school. They sat in front of massive control panels for the calutrons—machines used to enrich uranium. They were told to keep a needle between two marks. If the needle moved, they turned a knob. They didn't know they were separating Uranium-235 from Uranium-238. They didn't know their work would eventually level a city. In fact, they were actually better at the job than the PhDs. The scientists kept trying to figure out why the needles moved, while the girls just reacted and kept the machines steady.
Oak Ridge: The Secret City
Oak Ridge consumed roughly 1/7th of all the electricity generated in the United States at the time. It was a mud-filled, temporary town where people lived in "alphabet houses" (Type A, Type B, etc.). It was segregated, too. Black workers lived in "hutments"—plywood shacks with no plumbing—and performed the most dangerous, back-breaking labor of the entire project. They were essential, yet they were treated as disposable. That’s a part of the history that often gets glossed over in the movies.
The Spies in the Room
You can't have a $2 billion secret project without someone leaking it.
Klaus Fuchs is the big name here. He was a German-born British physicist who worked at Los Alamos. He was brilliant, quiet, and a total Soviet spy. He handed over the blueprints for the "Fat Man" implosion lens design to the USSR. Without him, the Cold War might have looked very different.
But he wasn't alone. Theodore Hall was an 18-year-old Harvard grad at Los Alamos. He also gave secrets to the Soviets because he was afraid a U.S. monopoly on nuclear weapons would be dangerous for the world. He was never prosecuted.
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The Hanford Site: Where Plutonium Was Born
While Oak Ridge dealt with uranium, the Hanford Site in Washington State was basically a plutonium factory. This place was massive. It took over 500 square miles of desert.
The people here were mostly construction workers and engineers. They built the B Reactor, the first full-scale nuclear reactor in history. It used Columbia River water for cooling. The scale of the engineering was unprecedented. Imagine building something that has never existed before, using materials that are literally lethal to touch, and doing it all in about 15 months.
That’s the kind of pressure these people were under.
The DuPont company ran the site. They were a chemical giant, and they brought a corporate efficiency to the project that the academic scientists initially scoffed at. But without DuPont’s industrial muscle, the Trinity test in New Mexico would have never happened.
Why the Diversity of the Group Mattered
The Manhattan Project wasn't just an American effort. It was a "Brain Drain" of Europe’s best minds.
- Niels Bohr: Escaped Nazi-occupied Denmark in the bomb bay of a British plane. He almost died from lack of oxygen because he didn't put his mask on right.
- Edward Teller: The man who would later push for the Hydrogen Bomb. He was brilliant but incredibly divisive.
- Richard Feynman: A young, eccentric genius who spent his free time at Los Alamos picking the locks of top-secret safes just to prove they weren't secure.
- Lilli Hornig: A female chemist who worked on plutonium. When the men tried to move her to a "safer" clerical job, she refused, eventually joining the team that worked on high explosives.
When you ask who was involved in the Manhattan Project, you're asking about a cross-section of humanity. You had Nobel laureates working alongside 19-year-old secretaries and janitors. You had soldiers and pacifists. You had people who thought they were saving the world and people who, after the war, felt they had helped destroy it.
The Ethical Ghost in the Machine
It’s easy to look at the list of names and see heroes or villains. It’s more complicated than that.
After the war, many of the scientists, including Oppenheimer himself, struggled with what they had done. The "Franck Report" was a document signed by several project scientists arguing that the bomb should be demonstrated in an uninhabited area first rather than dropped on a city. Their plea was ignored.
The involvement of these people didn't end in 1945. It sparked the Atomic Age, led to the creation of the AEC (Atomic Energy Commission), and basically set the stage for every geopolitical conflict for the next 80 years.
Real-World Impact and What You Should Do Next
The Manhattan Project is a masterclass in what happens when limitless funding meets absolute desperation. If you want to really understand the legacy of these people, you have to look beyond the weapons.
The project gave us:
- Nuclear Medicine: The isotopes used in PET scans and cancer treatments were a direct result of the research at Oak Ridge.
- Modern Computing: The massive calculations required for the implosion bomb pushed early computing forward.
- Big Science: This was the birth of the "National Laboratory" system we still use today for everything from climate change research to vaccine development.
Practical Steps to Learn More
If you're actually interested in the nitty-gritty of who was involved in the Manhattan Project, don't just watch the movies. Do this:
- Visit the Manhattan Project National Historical Park. It’s spread across three sites: Los Alamos (NM), Oak Ridge (TN), and Hanford (WA). You can actually stand in the spots where history was made.
- Read "The Making of the Atomic Bomb" by Richard Rhodes. It’s the definitive book. It’s thick, but it reads like a thriller.
- Check out the Voices of the Manhattan Project. It’s an oral history archive with hundreds of interviews from the people who were actually there—not just the famous ones, but the technicians and residents too.
- Research the "Downwinders." These were the people living near the Trinity site and the Hanford site who suffered from radiation exposure. It’s a vital, often ignored part of the project's human cost.
Understanding this project isn't about memorizing a list of names. It’s about realizing that 130,000 different lives converged to change the world forever, for better and for worse.