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Podcast Transcript

During the Second World War, the United States embarked on one of the greatest science and engineering projects the world had ever seen. 

Over 125,000 people took part in the program, the vast majority of which had no clue what it was for, and the total cost of the program was over a billion dollars at a time when a billion dollars was a lot of money. 

The end result was the most devastating weapon ever created, and it fundamentally changed the world.

Learn more about the Manhattan Project and how the atomic bomb was created on this episode of Everything Everywhere Daily.

I’ve done a fair number of episodes dealing with the development and creation of the atomic bomb. I’ve discussed various nuclear tests, the Nazi atomic bomb program, the Trinity test, as well a host of related subjects. 

 However, I haven’t done a full episode on the central subject in the development of the atomic bomb, the Manhattan Project.

The Manhattan Project was one of, if not the most important, scientific and engineering programs ever undertaken, and the legacy of the program can still be felt today. 

The story of the Manhattan Project actually begins in 1938 in Germany, in all places.

It began with the discovery of nuclear fission by German scientists Otto Hahn and Fritz Strassmann in December 1938, followed by theoretical explanations by Lise Meitner and Otto Frisch. 

They found that it was possible to split the nucleus of a Uranium atom and, in the process, release a tremendous amount of energy.

This news shook the world of physics. It didn’t take long for physicists to understand the ramifications of this discovery. A controlled chain reaction of splitting uranium atoms could lead to an incredible amount of energy that could be harnessed by society.

An uncontrolled chain reaction could lead to a tremendous explosion, the likes of which have never been seen in history. 

The fact that the discovery of fission had taken place in Nazi Germany terrified some of the leading physicists of the day. They feared what would happen if Hitler were to get his hands on such a weapon. 

Two of the physicists that were concerned were German-born Albert Einstein and Hungarian-born Leo Szilard. 

On August 2, 1939, just weeks before the German invasion of Poland, they wrote a letter to the American President, Franklin Roosevelt, urging the U.S. to start its own atomic research program. 

Roosevelt appointed Lyman Briggs of the National Bureau of Standards to head the Advisory Committee on Uranium.

The committee reported back to the president in November that uranium “would provide a possible source of bombs with a destructiveness vastly greater than anything now known.”

The United States was still not in the war, so limited funding was given to general research in an attempt to create an atomic reactor, or what at the time was called an atomic pile. 

In June 1940, the Advisory Committee on Uranium was renamed the National Defense Research Committee on Uranium.

The next important date was a year later on June 28, 1941. President Roosevelt signed an executive order that created the Office of Scientific Research and Development (OSRD). Its director was Vannevar Bush, a man who is worthy of his own future episodes. 

The OSRD took in the National Defense Research Committee on Uranium and renamed it the S-1 Committee, a purposely ambiguous name. They were given a budget to research uranium-235, the fissile isotope of uranium, and plutonium, which had been discovered in February of that year. 

Over in the UK, a separate research project was underway. In 1940, they established the MAUD committee to investigate the uses of uranium and, later, plutonium. They made some advancements in determining the critical mass of uranium-235 required for a bomb, as well as developing a plan for how to separate uranium-235 from uranium-238. 

As early as July 1940, the British offered to share what they knew with the United States. Physicist Henry Tizard came to the US to exchange information on RADAR and other technology. What he discovered was that at that time, the US atomic program was much smaller and further behind the British.

The British MAUD Committee eventually became the Tube Alloys Program, which was intended to be more than an investigation and an actual program to create an atomic weapon. However, the British didn’t have the resources to do so during the war. 

The Americans were not interested in sharing information at this time. 

Everything up until this point was mostly just theoretical investigations. What changed everything was the American entry into the war in December 1941. 

Now that the United States was at war with Germany, the need to develop a bomb before Germany became paramount. 

In early 1942. the S-1 Committee began planning for the actual development of a bomb. Ernest Lawrence of the Berkeley Radiation Laboratory proposed creating a nuclear chain reaction by July 1942 and an atomic bomb by January 1945.

His timeline seemed very ambitious. 

In June 1942, the project was transferred to the newly established Army Corps of Engineers Manhattan District. The Corps of Engineers named its districts after regions of major cities where the headquarters was located. When the project was first transferred to the Army, its first offices were located in Manhattan, and it was dubbed the Manhattan Project. 

The name stuck precisely because it wasn’t descriptive and conveyed nothing about the project’s purpose. 

The first order was business was selecting locations for the actual construction of the bomb. While over a dozen sites were used, there were three primary locations. 

The first was in Oak Ridge, Tennessee, just outside Knoxville. It was to be the primary facility for uranium enrichment. 

The second major facility was near the town of Hanford in central Washington state on the banks of the Columbia River. This was to be the processing center for the creation of Plutonium. 

On September 23,  Brigadier General Leslie R. Groves was appointed to lead the Manhattan Project.

On October 19,  Robert Oppenheimer was appointed as the scientific director of the Los Alamos Laboratory.

Los Alamos was to be the third major facility. This location was originally known as Project Y, the primary scientific laboratory where the bombs’ design and testing were conducted. 

It was decided that Project Y should be located in a remote area, and the selected area in New Mexico was one near where Oppenheimer owned a ranch. 

In December 1942, Enrico Fermi and his team at the University of Chicago developed the world’s first human-made self-sustaining nuclear chain reaction. 

Construction began on the facilities in Oak Ridge and Hanford in January 1943, and the Los Alamos Center opened in March. 

In April, Oak Ridge received its first shipment of uranium, and by August, its first nuclear reactor, the X-10 Graphite Reactor, began operation. 

Here, I should note that when the story of the Manhattan Project is often depicted in movies and television, it almost always revolves around Los Alamos. 

This is understandable as this was where all of the celebrity scientists were assembled. For perhaps the only time in history, a collection of some of the world’s greatest scientists all lived and worked in close proximity to each other. 

Although vitally important, the Los Alamos facility was a small part of the overall program. The vast majority of money and staff were employed at Oak Ridge and Hanford. 

While the team at Los Alamos was busy working on the designs of the bomb, no mater what design they used, the raw components of the bomb were going to be some combination of uranium-235 and plutonium-239.

Creating these raw materials was the single most challenging part of the entire Manhattan Project. This was what many physicists thought was going to be the thing that prevented the bomb from being built. 

Uranium comes in two naturally occurring isotopes: U-238, which makes up 99.3% of all natural uranium, and U-235, which makes up 0.7%. 

The problem is that both U-238 and U-235 are the same element and behave exactly the same chemically. There is no chemical process you can use to separate one from the other. 

There were two different methods that were proposed for how to separate the different isotopes of uranium.

The first was electromagnetic separation. This was a highly inefficient method that used the property that a magnetic field would deflect charged particles according to their mass. As the two isotopes had slightly different masses, you could separate one from the other. 

However, this was painfully slow as you had to do it almost atom by atom. I remember a professor who ran the mass spectrography lab when I was in school, explaining how he theoretically could enrich uranium with his mass spectrometer using this technique, but it would take decades to get an amount you could even manipulate. 

This was the first method pursued not because it was the best method but because it was known that it would work. 

Another method was gas diffusion. This method was much more promising but had bigger technical challenges. For starters, you had to make uranium hexafluoride, a highly corrosive gas. You used the property that when gasses passed through a semipermeable membrane, lighter mass gas particles tended to go through before heavier ones. 

You could separate the uranium hexafluoride gas that contained U-238 this way. However, you had to iterate it over and over and over. 

In November 1942, a gas diffusion plant was approved and was given the code name K-25. When the plant was finished in 1944, the K-25 facility was the world’s largest building.  It had over 5,264,000 square feet or 489,000 square meters of floor space and a volume of 97,500,000 cubic feet or 2,760,000 cubic meters. 

Finally, a liquid thermal diffusion plant was built. Thermal diffusion takes advantage of the property of fluids that, over a temperature gradient, lighter molecules move towards the hotter side, with heavier ones on the cold side.

Over in Hanford, they were working on creating plutonium-239, an element that is not found in nature. To do this, they created three nuclear reactors where they bombarded uranium-238 with neutrons. Some of these uranium atoms would then decay after a series of steps into Pu-239. 

As plutonium wasn’t natural, scientists had no idea how plutonium behaved chemically, so they had to figure out how to separate uranium from plutonium, which required plutonium that could be used for experimental research. 

To put the relative sizes of each facility into perspective, the Los Alamos facility had about 8,000 people working there, including families of the scientists. 

Oak Ridge had a total workforce of about 75,000 people, and Hanford had about 50,000. 

This was on top of building some of the biggest industrial facilities in the world. 

One of the big problems they had was keeping operational secrecy with so many people working there. The vast majority of the over 125,000 people who worked in some way on the Manhattan Project had no idea what they were working on. They just knew it was something scientific for the war effort.

About 85,000 people were construction workers, and another 40,000 worked at the plants.

Most people only knew their small role and didn’t know what anyone else was doing. 

The total cost of the Manhattan Project was $1.845 billion by the end of the war. While that was an enormous amount of money for the 1940s, it actually only represented about nine days’ worth of spending during the war. Inflation-adjusted, it would be about $25 billion dollars today.

Despite the large budget, almost no one in Congress was aware of the program. Near the end of the war in Europe in March 1945, there were only seven members of Congress who had been briefed on the Manhattan Project. 

The end result of the work of tens of thousands of people, almost two billion dollars in spending, and some of the largest buildings on the planet was actually shockingly small. 

Oak Ridge managed to create a whopping 50 kilograms or 110 pounds of Uranium-235, which should be noted as a very dense metal. 

Hanford managed to produce six kilograms or 13.2 pounds of Plutonium-239. 

Despite the seemingly small amount, the U-235 was enough to create the Little Boy bomb dropped on Hiroshima on August 6, 1945.

The Plutonium-239 was enough for two bombs. The one used at the Trinty Test explosion and the Fat Man bomb dropped on Nagasaki. 

There actually was a great deal of doubt as to if they should conduct the Trinity test explosion because of the enormous cost of the plutonium involved. 

The Manhattan Progect was also one of the largest single science and engineering programs that the world had ever seen, and the biggest until the Apollo Program. 

It changed the world. Not only did it end the Second World War, but it ushered the world into an era of nuclear weapons.