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Mushroom cloud over Hiroshima, August 6, 1945THE ATOMIC BOMBING OF HIROSHIMA
(Hiroshima, Japan, August 6, 1945)
Events > Dawn of the Atomic Era, 1945

In the early morning hours of August 6, 1945, a B-29 bomber named Enola Gay took off from the island of Tinian and headed north by northwest toward Japan.  The bomber's primary target was the city of Hiroshima, located on the deltas of southwestern Honshu Island facing the Inland Sea.  Hiroshima had a civilian population of almost 300,000 and was an important military center, containing about 43,000 soldiers.

Little Boy at Tinian Island, August 1945The bomber, piloted by the commander of the 509th Composite Group, Colonel Paul Tibbets, flew at low altitude on automatic pilot before climbing to 31,000 feet as it neared the target area.  At approximately 8:15 a.m. Hiroshima time the Enola Gay released "Little Boy," its 9,700-pound uranium gun-type bomb, over the city.  Tibbets immediately dove away to avoid the anticipated shock wave.  Forty-three seconds later, a huge explosion lit the morning sky as Little Boy detonated 1,900 feet above the city, directly over a parade field where soldiers of the Japanese Second Army were doing calisthenics.  Though already eleven and a half miles away, the Enola Gay was rocked by the blast.  At first, Tibbets thought he was taking flak.  After a secondEnola Gay returning from Hiroshima mission, Tinian Field, August 6, 1945 shock wave (reflected from the ground) hit the plane, the crew looked back at Hiroshima.  "The city was hidden by that awful cloud . . . boiling up, mushrooming, terrible and incredibly tall," Tibbets recalled.  The yield of the explosion was later estimated at 15 kilotons (the equivalent of 15,000 tons of TNT).

On the ground moments before the blast it was a calm and sunny Monday morning.  An air raid alert from earlier that morning had been called off after only a solitary aircraft was seen (the weather plane), and by 8:15 the city was alive with activity -- soldiers doing their morning calisthenics, commuters on foot or on bicycles, groups of women and children workingVictim of atomic attack with the pattern of her clothing burned into her back. outside to clear firebreaks.  Those closest to the explosion died instantly, their bodies turned to black char.  Nearby birds burst into flames in mid-air, and dry, combustible materials such as paper instantly ignited as far away as 6,400 feet from ground zero.  The white light acted as a giant flashbulb, burning the dark patterns of clothing onto skin (right) and the shadows of bodies onto walls.  Survivors outdoors close to the blast generally describe a literally blinding light combined with a sudden and overwhelming wave of heat. (The effects of radiation are usually not immediately apparent.)  The blast wave followed almost instantly for those close-in, often knocking them from their feet.  Those that were indoors were usually spared the flash burns, but flying glass from broken windows filled most rooms, and all but the very strongest structures collapsed.  One boy was blown through the windows of his house and across the street as the house collapsed behind him.  Within minutes 9 out of 10 people half a mile or less from ground zero were dead.

Before and After aerial photographs of HiroshimaPeople farther from the point of detonation experienced first the flash and heat, followed seconds later by a deafening boom and the blast wave.  Nearly every structure within one mile of ground zero was destroyed, and almost every building within three miles was damaged.  Less than 10 percent of the buildings in the city survived without any damage, and the blast wave shattered glass in suburbs twelve miles away.  The most common firstHiroshima mushroom cloud (picture taken from the ground) reaction of those that were indoors even miles from ground zero was that their building had just suffered a direct hit by a bomb.  Small ad hoc rescue parties soon began to operate, but roughly half of the city's population was dead or injured.  In those areas most seriously affected virtually no one escaped serious injury.  The numerous small fires that erupted simultaneously all around the city soon merged into one large firestorm, creating extremely strong winds that blew towards the center of the fire.  The firestorm eventually engulfed 4.4 square miles of the city, killing anyone who had not escaped in the first minutes after the attack.  One postwar study of the victims of Hiroshima found that less than 4.5 percent of survivors suffered leg fractures.  Such injuries were not uncommon; it was just that most who could not walk were engulfed by the firestorm.

"A-bomb Dome" amidst ruins of Hiroshima (the dome is now a World Heritage Site).Even after the flames had subsided, relief from the outside was slow in coming.  For hours after the attack the Japanese government did not even know for sure what had happened.  Radio and telegraph communications with Hiroshima had suddenly ended at 8:16 a.m., and vague reports of some sort of large explosion had begun to filter in, but the Japanese high command knew that no large-scale air raid had taken place over the city and that there were no large stores of explosives there.  Eventually a Japanese staff officer was dispatched by plane to survey the city from overhead, and while he was still nearly 100 miles away from the city he began to report on a huge cloud of smoke that hung over it.  The first confirmation of exactly what had happened came only sixteen hours later with the announcement of the bombing by theCasualties in a makeshift hospital, Hiroshima United States.  Relief workers from outside the city eventually began to arrive and the situation stabilized somewhat.  Power in undamaged areas of the city was even restored on August 7th, with limited rail service resuming the following day.  Several days after the blast, however, medical staff began to recognize the first symptoms of radiation sickness among the survivors.  Soon the death rate actually began to climb again as patients who had appeared to be recovering began suffering from this strange new illness.  Deaths from radiation sickness did not peak until three to four weeks after the attacks and did not taper off until seven to eight weeks after the attack.  Long-range health dangers associated with radiation exposure, such as an increased danger of cancer, would linger for the rest of the victims' lives, as would the psychological effects of the attack.

Devastation at HiroshimaNo one will ever know for certain how many died as a result of the attack on Hiroshima.  Some 70,000 people probably died as a result of initial blast, heat, and radiation effects.  This included about twenty American airmen being held as prisoners in the city.  By the end of 1945, because of the lingering effects of radioactive fallout and other after effects, the Hiroshima death toll was probably over 100,000.  The five-year death total may have reached or even exceeded 200,000, as cancer and other long-term effects took hold.

At 11:00 a.m., August 6 (Washington D.C. time), radio stations began playing a prepared statement from President Truman informing the American public that the United States had dropped an entirely new type of bomb on the Japanese city of Hiroshima -- an "atomic bomb." Truman warned that if Japan still refused to surrender unconditionally, as demanded by the Potsdam Declaration of July 26, the United States would attack additional targets with equally devastating results.  Two days later, on August 8, the Soviet Union declared war on Japan and attacked Japanese forces in Manchuria, ending American hopes that the war would end before Russian entry into the Pacific Fat Man at Tinian Island, August 1945theater.  By August 9th, American aircraft were showering leaflets all over Japan informing its people that "We are in possession of the most destructive explosive ever devised by man.  A single one of our newly developed atomic bombs is actually the equivalent in explosive power to what 2,000 of our giant B-29s can carry on a single mission.  This awful fact is one for you to ponder and we solemnly assure you it is grimly accurate.  We have just begun to use this weapon against your homeland.  If you still have any doubt, make inquiry as to what happened to Hiroshima when just one atomic bomb fell on that city."  Meanwhile, Tibbets's bomber group was simply waiting for the weather to clear in order to drop its next bomb, the plutonium implosion weapon nicknamed "Fat Man" (left) that was destined for the city of Nagasaki.

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Sources and notes for this page.

Portions of the text for this page were adapted from, and portions were taken directly from the Office of History and Heritage Resources publication: F. G. Gosling, The Manhattan Project: Making the Atomic Bomb (DOE/MA-0001; Washington: History Division, Department of Energy, January 1999), 51-53.  Also used was the report on "The Atomic Bombings of Hiroshima and Nagasaki" in the official Manhattan District History, produced by the War Department in 1947 at the direction of Leslie Groves, especially pages 1-19; the "Atomic Bombings" document is available in the University Publications of America microfilm collection, Manhattan Project: Official History and Documents (Washington: 1977), reel #1/12; the report itself is a government document.  Tibbets's description is from Paul W. Tibbets, "How to Drop an Atom Bomb," Saturday Evening Post 218 (June 8, 1946), 136.  The estimate of Little Boy's yield is from United States Nuclear Tests, July 1945 through September 1992 (DOE/NV-209-REV 15; Las Vegas, NV: Nevada Operations Office, Department of Energy, December 2000), vii.  Summaries of Hiroshima and Nagasaki casualty rates and damage estimates appear in Leslie R. Groves, Now It Can Be Told (New York: Harper & Row, 1962), 319, 329-330, 346, and Vincent C. Jones, Manhattan: The Army and the Atomic Bomb, United States Army in World War II (Washington: Center of Military History, United States Army, 1988), 545-548.  A translation of the leaflets dropped on Japan in between Hiroshima and Nagasaki can be found in Dennis Merrill, ed., Documentary History of the Truman Volume 1, The Decision to Drop the Atomic Bomb on Japan (Bethesda, MD: University Publications of America, 1995), 194-195.  The photograph of the mushroom cloud is courtesy the United States Air Force (USAF) (via the National Archives (NARA)).  The photographs of Little Boy and Fat Man are courtesy the U.S. Army Corps of Engineers (via NARA).  The photograph of the Enola Gay landing at Tinian Island is courtesy the USAF.  The photograph of the woman with burns on her back is courtesy the U.S. Army Corps of Engineers (via NARA).  The photographs of the mushroom cloud taken from the ground and of the debris (including the Hiroshima Peace Memorial (Genbaku "A-bomb" Dome) are courtesy the Federation of American Scientists.  The photographs of the hospital and of the lone soldier walking through an almost-completely leveled portion of the city are courtesy the Department of the Navy (via NARA); the former was taken by Wayne Miller.

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