Seventy years after the destruction of Hiroshima and Nagasaki by nuclear weapons, David Kaiser investigates the legacy of 'the physicists' war'. ... The Second World War marked an unprecedented mobilization of scientists and engineers, and a turning point in the relationship between research and the state. By the end of the war, the nuclear weapons project, code-named the Manhattan Engineer District, absorbed thousands of researchers and billions of dollars. It sprawled across 30 facilities throughout the United States and Canada, with British teams working alongside Americans and Canadians. Allied efforts on radar swelled to comparable scale. ... the term had been coined long before August 1945, and originally it had nothing to do with bombs or radar. Rather, the physicists' war had referred to an urgent, ambitious training mission: to teach elementary physics to as many enlisted men as possible. ... Both views of how scientists could serve their nations — the quotidian and the cataclysmic — have shaped scientific research and higher education to this day.