What was the Manhattan Project?
The Manhattan Project was a crash program, a no expense spared project, that sought to create the first atomic bomb. This was necessary because Allied intelligence forces had determined that Hitler and the Nazis were well on their way to creating a superweapon, the nuclear bomb. The Americans needed to get the atomic bomb before Hitler. If Hitler was able to get it first, the Nazis would win the war. Most of the work during the Manhattan Project was done at a secret laboratory in New Mexico, known as Los Alamos. The project was led by physicist J. Robert Oppenheimer and was a joint effort between the US, Canada, and the UK. The US spent the most money and contributed the most resources to the program, however.
Where did the name come from?
The ‘Manhattan Project’ is a code name. There are a few reasons for this name. One reason was that a lot of research into uranium fission (the process behind some atomic bombs, like the one used at Hiroshima) took place at Colombia, a university in New York. Also, there were many warehouses and laboratories in Manhattan that were working on the project. Lastly, there was a big headquarters building in Manhattan that handled administrative tasks. So, the Manhattan project was deeply rooted in that borough of New York City.
At the time, the total cost of the Manhattan project was two billion US dollars. In 2020 dollars that is equal to almost twenty-nine billion dollars, or 626,000 bitcoin! The US government basically spent whatever was necessary to beat the Germans and develop an atomic weapon. They did this even though they were not entirely sure at the beginning whether nuclear bombs were scientifically or practically possible.
Dates and times
The Manhattan Project started in 1939. On August 2, 1939, two physicists, Albert Einstein and Leo Szilard called for US President Franklin Roosevelt to start an exploratory program to try to determine if nuclear bombs were possible. They too were afraid that Hitler would get the bomb first.
The Manhattan Project started soon after, with Roosevelt’s approval. It was small at first and confined to a few labs. Scientists mostly studied the properties of uranium, a heavy element that is fissile (it can split). By 1942 the urgency of the project ramped up because the US was now in the war and the fear of Hitler intensified. By 1943 a secret and enormous laboratory/city had been built in New Mexico to be the home of the work on the atomic bomb. This laboratory was called Los Alamos. By 1945 the bomb was ready.
The Manhattan project was ultra top secret. Most people who were working on the project had no idea what they were working on. They did not know that they were creating a bomb. They just did their specialized part and only knew about the one obscure piece of the whole that they had to know about to do their job. Only the top officials and leaders of the project knew what was really going on. All of this secrecy did not prevent the Soviet Union from stealing the designs of the atomic bombs. There were a few Soviet spies in the Manhattan project (Klaus Fuchs for example) that stole enough information for the Soviet Union to later copy the US’ design. Although the Soviet Union was our ally during World War Two, the relationship was tense. The Cold War was about to start.
How does fission work?
Atomic bombs work by splitting atoms (nuclear fission). This releases a lot of energy. Here is a diagram to illustrate the process.
The Urainium Gun Design
The first design that the many physicists at the Manhattan Project came up with was the uranium gun bomb design. In this type of device, a larger mass of uranium with a hole in the center is fired down a gun barrel and meets a smaller uranium slug. This target slug fits in the projectile’s hole. The larger piece of uranium is the projectile because of the neutron reflectors surrounding the target and problems with pre-detonation and unwanted criticality. This was not declassified until recently. But, combined, the two pieces of Uranium make a supercritical mass. The term critical mass just means that there is enough nuclear material to sustain a chain reaction. And supercritical means that this chain reaction grows, explosively. Nuclear fission takes place uncontrollably and the uranium gun bomb explodes.
The Plutonium Implosion Design
The second design was a plutonium implosion type bomb. There were two designs. This was because the leaders of the project wanted to make sure that if one type was impossible, the other could still be made. In the plutonium implosion design, precisely shaped explosives called explosive lenses surround a central plutonium core. The explosives are all detonated at once. The shock wave converges on the core, an implosion. This causes the core to become smaller and denser. When plutonium, or any other fissile material, becomes denser, it forms a critical mass. Neutrons are released by an initiator and the chain reaction starts. Boom. Explosion. The process and design are a little more complicated though.
Problems and impracticalities
Making the atomic bomb was difficult. Here are a few of the problems that the scientists ran into:
- Uranium 238 (an isotope) is very common. Ninety-nine percent of all uranium on Earth is 238. But uranium 238 does not split easily. No amount of it will be able to sustain a chain reaction. Uranium 235 can sustain a chain reaction pretty easily. But ,it is very rare (less than 1 percent of natural uranium). This is due to its half life being shorter than the age of Earth (700 million years). A bomb needed almost pure U235. But U235 and U238 are chemically the same. So the separation had to be done based on the small difference in mass. Big separation plants had to be made (centrifuges and gaseous diffusion).
- Plutonium does not exist in nature. So it had to be manufactured in nuclear reactors at Hanford Washington. This was expensive and took a long time.
- Explosive lenses had to be invented.
By July of 1945, the first atomic bomb had been made. Both designs, plutonium, and uranium had been figured out and were being manufactured. The scientists were so sure that the uranium gun would work that they did not even need to test it. But the plutonium bomb was more complicated, and no one knew for sure if it would work. Hanford Site had produced two bomb cores worth of plutonium, so they decided to use one to test the bomb. They assembled a plutonium implosion device, called The Gadget, and set it off in the New Mexico Desert. This test was called Trinity, and it took place on July 16, 1945. The Gadget exploded with the force of 22,000 tons of TNT (22 Kilotons).
Germany had already surrendered, so they were not a threat anymore by the time that the bombs were ready. But the war in the Pacific with Japan was dragging on. It looked like the US was going to have to conduct a terrible and deadly invasion of Japan. Officials, like president Harry Truman, did not want an invasion to take place. So, Truman authorized the use of the new atomic bombs against Japan.
At 2:45 AM, on August 6, 1945, a B-29 bomber plane called the Enola Gay took off from an island in the Pacific, Tinian, with an atomic bomb on board. A few hours later uranium gun style bomb, named Little Boy, was dropped on Hiroshima, a big city with a military presence and factories. It exploded at 1,900 feet at 9:15 AM on August 6, 1945. Hiroshima had been chosen in part because it was relatively untouched by the war. The US wanted to show how Hiroshima had been completely destroyed in one fell swoop by America’s powerful new weapon. Around 80,000 people died instantly due to the thermal pulse and blast effects. Around 70,000 more died in the coming months due to radiation. It was very bad.
Hiroshima did not cause the Japanese generals to surrender. So, three days later, on August 9, 1945, the US dropped a second atomic bomb on Nagasaki. The target was another industrial city in Japan. The original target was Kokura, but the weather was bad so the bombing was called off. This bomb was of the plutonium implosion type. It was more powerful, around 21 kilotons, and was named Fat Man. But, Nagasaki was more spread out than Hiroshima so fewer people died. Around 35,000 people died instantly and 35,000 more died in the coming days from radiation poisoning.
The Japanese high command decided that they could not let more cities be destroyed completely. Also, the Soviet Union had just declared war on the Japanese, on August 8. Japan knew that it could not win against atomic weapons and the Red Army.
So, they agreed to unconditionally surrender. This was lucky for the US because the material for a third bomb core had not been created yet. And Truman was very reluctant to bomb so many civilians again. The war was over. The bombs dropped on Hiroshima and Nagasaki remain the only two nuclear weapons to ever be used in combat. Let us hope that it stays that way.
Postwar: The Superbomb (Hydrogen Bomb)
For people like Edward Teller, a nuclear physicist who worked on the Manhattan Project, atomic bombs (nuclear fission) were not powerful enough. This was partly because Russia got the atomic bomb in 1949 and the US did not have an advantage anymore. So, the hydrogen bomb was conceived. The hydrogen bomb, also known as the thermonuclear bomb, fuses atoms instead of splitting them. A fission bomb sets off the much more powerful fusion chain reaction in a heavy isotope of hydrogen. The first hydrogen bomb to be tested was called Ivy Mike. It was tested in 1952. Mike was seven hundred times the power of the Hiroshima bomb with a yield of ten megatons. Almost all nuclear weapons in the US’s arsenal today are hydrogen bombs.
Rhodes, Richard. The Making of the Atomic Bomb. New York: Simon & Schuster, 1986. Print.
Rhodes, Richard. Dark sun : the making of the hydrogen bomb / Richard Rhodes Simon & Schuster New York 1995
History.com Editors. Manhattan Project. 26 July 2017, www.history.com/topics/world-war-ii/the-manhattan-project.
“Calculate the Value of $2.00 in 1945.” Calculate the Value of $2.00 in 1945. How Much Is It Worth Today?, H Brothers Inc, www.dollartimes.com/inflation/inflation.php?amount=2&year=1945.
“Manhattan Project.” Manhattan Project: CTBTO Preparatory Commission, www.ctbto.org/nuclear-testing/history-of-nuclear-testing/manhattan-project/#:~:text=The%20scientific%20research%20was%20directed,23%20billion%20in%202007%20dollars).
“Atomic Bombings of Hiroshima and Nagasaki.” Wikipedia, Wikimedia Foundation, 22 Feb. 2021, en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_and_Nagasaki.
Broad, William J. “Why They Called It the Manhattan Project.” The New York Times, The New York Times, 30 Oct. 2007, www.nytimes.com/2007/10/30/science/30manh.html.