The Manhattan Project

John Belanger
March 21, 2013

Submitted as coursework for PH241, Stanford University, Winter 2013


Fig. 1: Nagasaki after "Fat Man" bombing. (Source: Wikimedia Commons)

By 1950, an estimated 340,000 people had died from the effects of the atomic bombs dropped on Hiroshima and Nagasaki. [1] I begin with that fact because while this paper treats the Manhattan Project in an academic manner, I do not forget the tragic human cost. My purpose here, though, is to present details of the project itself from my reading of Jeff Hughes' book, The Manhattan Project, aided by some supplemental sources, most significantly an Atomic Heritage Foundation publication which brings together a collection of contemporaneous facts and observations from those directly involved in the undertaking. [1,2] I here aim to concisely answer the basic "reporter" questions: the who, what, when, where, and why of the endeavor that brought nuclear weapons into being.

Scientific Developments

Before World War II, and even before World War I, physicists were making great headway in understanding the inner workings of the atom's nucleus. It is telling that in 1914, science fiction was already covering nuclear weapons and energy. [2] Supposedly, Hungarian physicist Leo Szilard was fascinated by that idea from a book by H.G. Wells and later came to the conclusion that chain reactions releasing massive amounts of energy from the atom's nucleus might actually be possible. On December 21, 1938, a major discovery catapulted the nuclear field and brought that possibility of catastrophic weapons much farther from fiction to feasible reality. [2] In Germany, Otto Hahn and Fritz Strassmann had found a surprising result: uranium, when struck by neutrons, could form barium, an element of half its mass. [1] The team wrote to their colleague, Lise Meitner, who being Jewish, had earlier fled to Sweden. [1] While on a walk, she and her nephew, Otto Frisch, speculated on the results and struck upon the idea of nuclear fission. [2] Almost by accident, a discovery was made that changed the course of history.

Political Developments

The rise of the Nazis in Germany in 1933 sent many scientists like Lise Meitner abroad. [2] The fascists in Italy too came to power, and when Enrico Fermi left to collect the 1938 Nobel Prize for Physics, he never returned. [1] Fermi became instrumental in nuclear physics research conducted in the United States. When Germany occupied Czechoslovakia and halted uranium exports, it raised the eyebrows of scientists like Szilard who thought the Nazis might make use of research like Fermi's. [2] Along with Eugene Wigner, Szilard convinced Albert Einstein to alert the U.S. government and drafted Einstein's famous letter warning President Roosevelt in 1939 about the possibility of Germany developing powerful, new weapons. [2] With World War II looming in Europe, Roosevelt took the warning seriously, even though America was still at peace. The president assembled a team including members of the Army and Navy to consider Einstein's "suggestion regarding the element of uranium." [2]

Birth of the Manhattan Project

Roosevelt formally approved the creation of an advisory board on matters nuclear in October 1939. [2] By the spring of 1940, Vannevar Bush, Vice President of the Massachusetts Institute of Technology, was head of a revamped effort called the National Research Defense Council. [1] Researchers like Fermi at Columbia University and others scattered across the country were consolidated at the University of Chicago in the Metallurgical Laboratory or "Met Lab," a cover term for the nuclear research facility. [1] The Army Corps of Engineers created a special division that would handle the construction projects needed to produce atomic bomb materials and the actual bomb itself. The division was headquartered in Manhattan, New York and was thus given the suitable code name of Manhattan Engineering District (MED), or more commonly, the Manhattan Project. [1] On September 17, 1942, General Leslie Groves took command of MED and brought his dynamic drive and experience constructing the Pentagon to bear. [1] The Manhattan Project had begun.


Nuclear work was so radically new, that proper safety measures were not certain and site locations were chosen based on this. [2] DuPont, the chemical company, was contracted to produce plutonium. Out of the company's liability concerns, the military's secrecy concerns, and the practical need for electricity and railroads, a site at Hanford, Washington was chosen. [3] This is where the plutonium produced for the bomb over Nagasaki was produced. [2] The location was remote to reduce the potential risks from hazardous gases created during processing and risks posed by "unknown and unanticipated factors" that might be discovered by DuPont when the processes became less nascent. [3]

For uranium, the production facility would have access to large amounts of power from the Tennessee Valley Authority at a site called Oak Ridge. This plant in Tennessee is where the uranium for testing was produced during the Manhattan Project and where the uranium came from for the "Little Boy" bomb over Hiroshima. [1]

Another location was needed where research on bomb design could be centralized, away from any possible enemy airstrikes and somewhere that secrecy could be maintained. [1] Robert Oppenheimer, a physics professor at the University of California, Berkeley and in charge of coordinating bomb design, suggested a place in the mountains of New Mexico where he had gone as a child. [1] Construction began, and the Los Alamos laboratory opened in April 1943. [1]

Fig. 2: The Trinity test, July 16, 1945. (Source: Wikimedia Commons)


General Groves later remarked that while haste often makes waste, haste was required in the Manhattan Project as it was a race against the Germans to produce a weapon that could change the course of the war. [3] While scientists worked frantically, the subject was complex and took time.

Groves and Oppenheimer organized work in a unique way. Scientists would eventually come to work in teams with labels such as "G division," which focused on the bomb "gadget" and "X Division," which worked on explosives. [1] While the work was much more organized than it had been previously, research still proceeded most rapidly using a trial and error manner. [1] When one pathway seemed most promising effort was shifted to focus on developing that area further. The field was so new however, that setbacks were common. In the very beginning, it was not certain that a fission bomb was even possible in a realistic time frame. That changed when the first milestone of producing the bomb was achieved: a chain reaction. In December 1942, Fermi, working at the Met Lab, produced the world's first sustained nuclear chain reaction using a large pile of uranium and graphite stacked at a sports arena in Chicago. [1] The bomb was possible.

The original concept for the nuclear devices was using a gun to shoot a bullet of uranium into a subcritical mass of uranium to rapidly reach criticality and unleash a vast nuclear force. Plutonium was of interest because it requires a much lower mass to reach criticality, at the time estimated at 5 kilograms versus 15 for uranium. [1] The higher fissile character of plutonium meant that a high velocity bullet would be required. The uranium bomb could use a slower bullet and shorter gun that would fit into a design called "Little Boy." [1] To create a higher velocity bullet for the plutonium bomb, a 17-foot long gun was needed in a design called "Thin Man." [1]

Requiring the smallest amount of fissile material possible was important because a major hurdle was producing enough uranium and plutonium at Oak Ridge and Hanford to be able to conduct research and eventually produce actual weapons. Enriching these materials was a new field and one major challenge was the inability to produce plutonium of the purity that the bomb designers at Los Alamos required. [1] The plutonium from Hanford included an isotope that was far more fissile than the design had calculated for. [1] The design of "Thin Man" would not work.

Researchers sought another alternative for plutonium. Designing a different type of gun or finding ways to purify the plutonium to include only the less fissile isotope were both seen as options that would require too much time. [1] Instead, the design changed to using explosives to rapidly force the subcritical components together in an implosion. This design was called "Fat Man." [1]

Finally, in early May 1945 the uranium bomb design, "Little Boy," was complete and only awaiting sufficient uranium from Oak Ridge to be assembled. [1] By July, it was ready for combat use. [1] The plutonium implosion device, "Fat Man," was hurriedly tested on July 16, 1945 ahead of President Truman's meeting with Churchill and Stalin at Potsdam. [1] It was called the Trinity test, and it the world's first nuclear explosion. [1] The bombs which would be used on Hiroshima and Nagasaki in less than a month had been created.


At its height, the Manhattan Project was at the scale of the entire US automobile industry and cost a total of $2.2 billion. [1] While it received the highest priority, it should also be noted that other military projects were substantial. [1] The US spent even more, $3 billion, developing radar technology. [1] Clearly the results of the Manhattan Project and the profound change it made in the balance of world power made it the most notorious program, however. After the bombing of Japan brought about the decisive end to World War II, physicists were "the aristocracy of post-war science." [1] As for the Manhattan Engineer District itself, in 1947, it became the Atomic Energy Commission (AEC), which continued to manage the national laboratories that had been established. [1] Finally, the AEC was re-branded in the 1980s to become the Department of Energy. [1]

© John Belanger. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] J. Hughes, The Manhattan Project: Big Science and the Atom Bomb (Icon Books, 2002).

[2] C. C. Kelly and R. Rhodes, The Manhattan Project: The Birth of the Atomic Bomb in the Words of Its Creators, Eyewitnesses, and Historians (Black Dog & Leventhal, 2009).

[3] M. S. Gerber, On the Home Front: The Cold War Legacy of the Hanford Nuclear Site, 3rd Ed. (Bison Books, 2007).