This report, compiled by the Manhattan Engineer District of the United States Army under the direction of Major General Leslie R. Groves, describes the effects of the atomic bombs which were dropped on the Japanese cities of Hiroshima and Nagasaki on August 6 and 9, 1945, respectively. It summarizes all the authentic information that was available on damage to structures, injuries to personnel, morale effect, etc., and which could be released in 1945 without prejudicing the security of the United States.