Canada and the Manhattan Project | The Canadian Encyclopedia


Canada and the Manhattan Project

Canada helped develop the world’s first nuclear reactors and nuclear arms. During the Second World War, Canada participated in British research to create an atomic weapon. In 1943, the British nuclear weapons program merged with its American equivalent, the Manhattan Project. Canada’s main contribution was the Montreal Laboratory, which later became the Chalk River Laboratory. (See Nuclear Research Establishments). This Allied war effort produced the atomic bombs dropped on the Japanese cities of Hiroshima and Nagasaki in 1945. It also led to the development of Canada’s nuclear energy industry.

Click here for definitions of key terms used in this article.


The field of nuclear physics emerged at the turn of the 20th century. In 1896, Henri Becquerel discovered radioactivity. The following year, J.J. Thompson discovered the electron. In 1898, Marie and Pierre Curie discovered radium and extensively documented the phenomenon of radiation. Another breakthrough came in 1905. That year, Albert Einstein introduced his theory of special relativity and the mass-energy equivalence, better known as E=MC2.

At around the same time at McGill University in Montreal, Harriet Brooks discovered that elements could decay into other elements, releasing radiation. Brooks was Canada’s first female nuclear physicist. Ernest Rutherford discovered the idea of a radioactive half-life and the radioactive element radon. Rutherford also distinguished between types of radiation. For this work, he received the Nobel Prize in Chemistry in 1908.

Photo of Harriet Brooks
Harriet Brooks, Montreal, QC, 1898

Scientific theories about splitting atoms to unleash their energy date back to before the First World War. The idea of using this technique in warfare appears as early as 1914 in the fiction of English writer H.G. Wells. Theory became reality in late 1938 when German chemist Otto Hahn discovered nuclear fission with Lise Meitner. Hahn had worked with Rutherford at McGill University in 1905–06.

The discovery of nuclear fission opened the door to the prospect of atomic bombs. This occurred less than a year before Germany invaded Poland in 1939 and set off the Second World War.

Canadian Nuclear Research

Canadian nuclear physicist George Laurence experimented with uranium fission as early as 1939–40. His goal was to develop a uranium-graphite reactor. Laurence carried out his experiments in Ottawa for the National Research Council. The uranium he used came from the Eldorado Mine in Port Radium, Northwest Territories. Laurence did not succeed in building a reactor. However, his experiments from 1940 to 1942 meant that the first human-made nuclear chain-reaction came close to being achieved in Canada.

Photograph of the Eldorado Mine

A miner hauling a car of silver radium ore, 340 feet below the surface, Eldorado Mine of Great Bear Lake (NWT), c. 1930.

Tube Alloys

The British government began to plan a nuclear weapons research project in 1940. Codenamed “Tube Alloys” when it launched the next year, it was the world’s first nuclear weapons research program. At first, Tube Alloys was based at the Cavendish Laboratory at the University of Cambridge. But the British were low on resources and wary of the threat posed by German bombers after the Battle of Britain. They therefore sought a partner nation for the project. Canada accepted a British request to relocate the research project in 1942. The cabinet minister for wartime production, C.D. Howe, authorized the development of the Montreal Laboratory. This was a joint Canadian-British research effort based at McGill University and the Université de Montréal.

Quebec Conference

At the Quebec Conference of 1943, Britain and the United States merged their nuclear weapons research into a single effort. Britain had been leading in nuclear research in the late 1930s and the early years of the war. But the conflict was draining resources and Britain had fallen behind. The joint effort agreed to in Quebec would later assume the codename of the US effort: the Manhattan Project.

Quebec Conference, 1943
US president Franklin D. Roosevelt, Canadian prime minister William Lyon Mackenzie King and British prime minister Winston Churchill at Quebec, August 1943.

Canada made three main contributions to the Manhattan Project. First, Canada supplied and processed uranium. The Americans used this uranium to research and develop atomic bombs. (Canada would continue to supply the US with uranium for military uses for about two decades after the war.) Second, Canada played an important role in researching the extraction and production of plutonium. Plutonium is also used in nuclear weapons. Third, Canada provided many researchers and scientists, as well as key facilities for research and production.

Chalk River and ZEEP

Research at the Montreal Laboratory moved to new facilities in Chalk River, Ontario in 1944. (See Nuclear Research Establishments). Chalk River had two experimental reactors. The first was known as ZEEP (Zero Energy Experimental Pile). On 5 September 1945, ZEEP achieved a sustained and controlled nuclear reaction using uranium and heavy water. It was the first nuclear reactor built and operated outside the United States. It could also generate plutonium from uranium.

The other experimental reactor was known as NRX (National Research Experimental). It would not go critical (i.e., sustain a nuclear chain reaction) until 1947. Together, the ZEEP and NRX experimental reactors would lay the foundation for the development of the CANDU nuclear reactor. The CANDU reactor is used in Canada and around the world.

Photo of a plant worker at the Chalk River Laboratory

A plant worker puts on shoes to protect against radioactivity.

The Montreal Laboratory closed in 1946 with its research programs consolidating at Chalk River. In 1952, Atomic Energy of Canada Ltd., a crown corporation, took over research at Chalk River. The corporation’s mandate from the federal government was to develop peaceful uses of nuclear energy, such as power generation.

The Dene of Déline

During the Manhattan Project, the Eldorado Mine in Port Radium, Northwest Territories, employed Dene people from the community of Déline to carry uranium. Some Dene believe that uranium from this mine became the fissile material in the bomb dropped on Hiroshima on 6 August 1945. This point is disputed by some historians, including Robert Bothwell, who wrote a history of the Eldorado Mining company in 1984. Bothwell suggests that the uranium the Dene carried was not pure enough to be used in the bomb. Whether or not it formed part of the weapon, at least some of this uranium was used in experiments that led to the development of nuclear arms and Canada’s nuclear industry.

Key Terms: Canada and the Manhattan Project


The emission of energy in the form of waves or particles moving through space or matter.


The spontaneous emission of energetic particles from some elements and isotopes as their atomic nuclei disintegrate.

Nuclear fission

The splitting of an atom’s nucleus, which causes the release of large amounts of energy.

Nuclear reactor

A structure that can sustain a controlled nuclear reaction in order to release energy.

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