Manhattan Project

The Manhattan Project was a research and development program during World War II that aimed to create the first nuclear weapons. Led by the United States, with help from the United Kingdom and Canada, it brought together scientists, engineers, and military leaders to achieve this goal. At its peak, the project employed nearly 130,000 people and cost about US$2 billion, which is equivalent to roughly $28 billion today.

The project was directed by Major General Leslie Groves of the U.S. Army Corps of Engineers, with nuclear physicist J. Robert Oppenheimer leading the Los Alamos Laboratory in New Mexico, where the actual bomb designs were developed. The name "Manhattan Project" came from the project's early headquarters in Manhattan, although its official code name was "Development of Substitute Materials."

Two main types of atomic bombs were developed: Little Boy, using enriched uranium, and Fat Man, using plutonium. The first successful test of a nuclear device, known as the Trinity test, took place on July 16, 1945, in New Mexico. Later that year, these bombs were used against Hiroshima and Nagasaki in Japan, leading to the end of World War II. The Manhattan Project also worked to gather intelligence on Germany’s nuclear efforts and faced challenges from Soviet atomic spies.

Origins

For a chronological guide, see Timeline of the Manhattan Project.

The discovery of nuclear fission in 1938 showed that an atomic bomb might be possible. Scientists worried that Germany might build one first. In 1939, a letter signed by Albert Einstein warned President Roosevelt about this danger. Roosevelt started a small committee to study uranium, but some scientists thought the work was too slow.

When World War II began, Britain shared its atomic research with the United States. An Australian scientist named Mark Oliphant visited American labs and convinced more scientists to take the project seriously. By late 1941, President Roosevelt decided to speed up the atomic program. After the attack on Pearl Harbor, the United States entered the war, and the project gained more urgency. Scientists began exploring different ways to separate the right kind of uranium and build reactors. The project grew quickly, with more money and attention as the fear of a German bomb pushed leaders to act.

Organization

Manhattan District

In June 1942, Major General Eugene Reybold chose Colonel James C. Marshall to lead the Army’s role in the Manhattan Project. Marshall set up offices in New York City, working closely with engineers and scientists. The project was initially called “Development of Substitute Materials,” but it was nicknamed the Manhattan District after the city where much of the work happened.

Later, Major General Leslie Groves took over leadership of the project. He brought in J. Robert Oppenheimer to help design the atomic bomb. The United States worked with the United Kingdom and Canada, sharing knowledge and resources. This teamwork was important for building the first nuclear weapons during World War II.

Main article: British contribution to the Manhattan Project

Project sites

!Los Alamos Project Y

Los Alamos Project Y

!Alamogordo Trinity test

Alamogordo Trinity test

!RichlandHanford Engineer Works

Richland
Hanford Engineer Works

!Oak RidgeClinton Engineer Works

Oak Ridge
Clinton Engineer Works

!BerkeleyRadiation Laboratory

Berkeley
Radiation Laboratory

Metallurgical Laboratory

Chicago Metallurgical Laboratory

!Ames Project

Ames Project

!Dayton Project

Dayton Project

!Montreal Laboratory

Montreal Laboratory

!Chalk River Laboratories

Chalk River Laboratories

!Inyokern Project Camel

Inyokern Project Camel

!MonticelloVanadium Corp.

Monticello
Vanadium Corp.

!UravanUS Vanadium Corp.

Uravan
US Vanadium Corp.

!Wendover Project Alberta

Wendover Project Alberta

!TrailCominco

Trail
Cominco

!Wabash River Ordnance Works

Wabash River Ordnance Works

!Morgantown Ordnance Works

Morgantown Ordnance Works

!Alabama Ordnance Works

Alabama Ordnance Works

!ClevelandNational Carbon Company

Cleveland
National Carbon Company

!St LouisMallinckrodt

St Louis
Mallinckrodt

!RochesterMedical Section

Rochester
Medical Section

A selection of US and Canadian sites important to the Manhattan Project. Research and production took place at more than thirty sites across the US, the UK, and Canada. Click on the location for more information.

• Purple: Fissile material production
• Orange: Feed materials production
• Green: Research
• Black: Logistics/other

Oak Ridge

Main article: Clinton Engineer Works

The Manhattan Project needed a big place to make special materials. Oak Ridge in Tennessee was chosen and built quickly. Thousands of people moved there to help with the work. The town grew fast, and by 1945, it had over 75,000 people.

Los Alamos

Main article: Project Y

Los Alamos in New Mexico was chosen as a quiet place to design the first nuclear weapons. It was far away from cities, which made it safer. Scientists and workers lived there in a special community while they did their important work.

Chicago

Main article: Metallurgical Laboratory

Near Chicago, scientists built one of the first nuclear reactors. This was a big step in learning how to control nuclear reactions. The reactor was hidden under a big stadium to keep it safe.

Hanford

Main article: Hanford Engineer Works

Hanford in Washington was chosen to make special materials for the nuclear weapons. It was far from big cities, which made it safer. Thousands of people lived there while they built and worked in the factories.

Canadian sites

Main article: Montreal Laboratory

Canada helped with research and making special materials. Scientists from Canada worked with teams in the United States. Different places in Canada made important parts for the project.

Heavy water sites

Main article: P-9 Project

Some special factories were built in the United States to make heavy water, which was needed for certain types of nuclear reactors. These factories used different methods to produce heavy water.

Uranium

The Manhattan Project needed uranium as its key material. Uranium was used to create fuel for reactors, produce plutonium, and make atomic bombs. Four main uranium deposits were known in 1940: in Colorado, northern Canada, Joachimsthal in Czechoslovakia, and the Belgian Congo. Most of these were under Allied control. In 1942, enough uranium was found to meet the project’s needs.

Uranium ore was processed into different forms for use. One method used nitric acid to create uranyl nitrate, which was then turned into uranium trioxide and uranium dioxide. Different techniques were tried to separate the rare uranium-235 isotope from the more common uranium-238. These included electromagnetic separation, gaseous diffusion, and thermal diffusion, each using unique technology to enrich the uranium for use in bombs.

Plutonium

The Manhattan Project developed two main types of nuclear weapons. One used plutonium, a material that can be made in special reactors. To create plutonium, uranium is bombarded with neutrons in a reactor. This turns it into another element called plutonium-239, which can be separated from the uranium and used in weapons.

Several important facilities were built to make and separate plutonium. The X-10 Graphite Reactor at Oak Ridge was an early test facility. Larger reactors were later built at the Hanford Site. These reactors produced the plutonium that was used in the first atomic bomb called "Fat Man," which used an implosion design to create a powerful explosion.

Personnel

At its peak in June 1944, the Manhattan Project employed about 129,000 workers, including construction workers, plant operators, and military personnel. Many highly skilled workers were needed, and it was challenging to find enough of them because of other wartime needs. The project included a few African-American scientists and technicians and had more women in technical roles than later government projects.

The Army provided some skilled workers through programs like the Army Specialized Training Program and the Special Engineer Detachment. The Women's Army Corps (WAC) also contributed, taking on technical and scientific tasks. The project's Medical Section, led by Stafford L. Warren, focused on health and safety for workers handling dangerous materials and conditions.

Secrecy

The Manhattan Project operated under strict secrecy during World War II. Only a few people knew about the project, and everyone involved followed strict rules to keep it hidden. Workers often did not know the purpose of their jobs, which helped protect the project from enemies.

The project faced challenges in keeping everything secret due to the large number of people involved and concerns about possible spying. Despite these challenges, the project succeeded in remaining mostly hidden until the end of the war.

Foreign intelligence

Main article: Alsos Mission

The Manhattan Project also worked to learn about other countries' efforts to build atomic bombs. They were especially worried that Germany might be close to creating its own weapon. To stop this, they carried out bombings and sabotage against important factories in German-occupied Norway. A special team called the Alsos Mission was formed to investigate scientific developments in enemy countries. This team followed the Allied armies as they moved across Europe, talking to scientists and searching places where work might have been done.

The Alsos Mission learned that Germany’s nuclear program had not advanced beyond small experiments. They also captured important materials and scientists from Germany, taking them to England for further study. This helped the Allies understand the progress of Germany’s atomic research and ensured valuable resources did not fall into the hands of the Soviet Union.

Atomic bombings of Hiroshima and Nagasaki

Main article: Atomic bombings of Hiroshima and Nagasaki

The United States decided to use the first atomic bombs near the end of World War II. Two cities in Japan, Hiroshima and Nagasaki, were chosen as targets because they were important military centers.

On August 6, 1945, an American plane dropped a bomb on Hiroshima. The explosion destroyed much of the city and caused many casualties. Three days later, on August 9, another bomb was dropped on Nagasaki, also causing great destruction. These events led to Japan’s decision to surrender, ending World War II. The use of these bombs remains a topic of discussion and debate among historians today.

After the war

After World War II, the Manhattan Project became famous for its role in developing the first nuclear weapons. The project officially ended on December 31, 1946, but its work continued to influence science and policy. Scientists and leaders received awards for their contributions, and the project helped start new ways to study and control nuclear energy.

The Manhattan Project faced many challenges after the war, including technical issues and changes in its staff. Some facilities were closed, and new methods were developed to improve nuclear technology. The project also played a role in early nuclear tests, showing the power of these new weapons. As the world grappled with the future of nuclear science, many scientists called for international control to prevent a dangerous arms race.

Cost

The Manhattan Project cost about $2 billion by the end of 1945, which is equivalent to around $28 billion today. Most of this money went to building factories to create the materials needed for the atomic bombs. During the war, Congress was not told about the project to keep it secret, and the funds were hidden in other bills.

The project produced three atomic bombs, with the average cost per bomb being about $500 million in 1945 dollars. This made it the second most expensive weapons project for the United States during the war, only behind the Boeing B-29 Superfortress.

Legacy

See also: Nuclear weapons in popular culture

The development of nuclear weapons during the Manhattan Project had major political and cultural effects. Reporting on the first nuclear tests helped people understand the power of these new technologies, which encouraged further development in many countries.

The project also created important research centers, such as the Los Alamos National Laboratory and Oak Ridge National Laboratory. These labs became leaders in big scientific projects and advanced computing. The project’s work helped start new fields like nuclear medicine, where special materials are used to diagnose and treat diseases. However, the rush to build these weapons also left behind difficult environmental problems that are still being cleaned up today.

The Manhattan Project National Historical Park was established on 10 November 2015.