The Second World War, with its emphasis on innovative weapons and defence technology, brought about massive changes in the role of scientists in Canada, the United States, and Great Britain. Canadian scientists, working through the auspices of the National Research Council and the Department of National Defence, made important contributions to the development of alliance warfare. Before 1939, Canada had only a minute military establishment and a limited industrial and academic capacity for research and development. With the outbreak of war, all this changed dramatically. This book explains how and why Canada was able to play in the big leagues of military technology, including the development of radar, RDX explosives, proximity fuses, chemical and biological warfare, and the atomic bomb. It also investigates the evolution of the Canadian national security state, which attempted to protect defence secrets both from the Axis powers and from Canada's wartime ally, the Soviet Union. The Science of War provides both a cross-disciplinary overview of the scientific and military activity of this period in several countries and a fascinating analysis of what the author calls 'Big Science' in Canada.