This report 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 is available on damage to structures, injuries to personnel, morale effect, etc., which can be released at this time without prejudicing the security of the United States. This report has been compiled by the Manhattan Engineer District of the United States Army under the direction of Major General Leslie R. Groves. Foreword Introduction The Manhattan Project Investigating Group Propaganda Summary of Damages and Injuries Main Conclusions The Selection of the Target Description of the Cities Before the Bombings Hiroshima Nagasaki The Attacks Hiroshima Nagasaki General Comparison of Hiroshima and Nagasaki General Description of Damage Caused by the Atomic Explosions Total Casualties The Nature of an Atomic Explosion Characteristics of the Damage Caused by the Atomic Bombs Calculations of the Peak Pressure of the Blast Wave Long Range Blast Damage Ground Shock Shielding, or Screening, from the Blast Flash Burn Characteristics of Injuries to Persons Burns Mechanical Injuries Blast Injuries Radiation Injuries Shielding from Radiation Effects of the Atomic Bombings on the Inhabitants of the Cities Appendix: Father Siemes' eyewitness account