Since 1945, when the first atomic bombs were dropped on the Japanese cities of Hiroshima and Nagasaki, nations across the world have feared the widespread destruction capabilities of nuclear weapons. The long-term effects of radiation and atmospheric pollution caused by nuclear explosions can last decades, centuries, or even millennia, making nuclear and radiological weapons one of the most critical risks for civilization on earth. Each day, DTRA is working to predict, understand, and address the effects of nuclear and radiological weapons. Using innovative science and technology, DTRA works with federal agencies and foreign governments to improve global preparedness and response capabilities.