The Effects of the Atomic Bombs as presented by United States Strategic Bombing Survey
The Attacks and Damage
1. The attacks.—A single atomic bomb, the first weapon of its type ever used against a target, exploded over the city of Hiroshima at 0815 on the morning of 6 August 1945. Most of the industrial workers had already reported to work, but many workers were enroute and nearly all the school children and some industrial employees were at work in the open on the program of building removal to provide firebreaks and disperse valuables to the country. The attack came 45 minutes after the ‘all clear’ had been sounded from a previous alert. Because of the lack of warning and the populace’s indifference to small groups of planes, the explosion came as an almost complete surprise, and the people had not taken shelter. Many were caught in the open, and most of the rest in flimsily constructed homes or commercial establishments.
The bomb exploded slightly northwest of the center of the city. Because of this accuracy and the flat terrain and circular shape of the city, Hiroshima was uniformly and extensively devastated. Practically the entire densely or moderately built-up portion of the city was leveled by blast and swept by fire. A ‘fire-storm,’ a phenomenon which has occurred infrequently in other conflagrations, developed in Hiroshima: fires springing up almost simultaneously over the wide flat area around the center of the city drew in air from all directions. The inrush of air easily overcame the natural ground wind, which had a velocity of only about 5 miles per hour. The ‘fire-wind” attained a maximum velocity of 30 to 40 miles per hour 2 to 3 hours after the explosion. The ‘fire-wind” and the symmetry of the built-up center of the city gave a roughly circular shape to the 4.4 square miles which were almost completely burned out.
The surprise, the collapse of many buildings, and the conflagration contributed to an unprecedented casualty rate. Seventy to eighty thousand people were killed, or missing and presumed dead, and an equal number were injured. The magnitude of casualties is set in relief by a comparison with the Tokyo fire raid of 9–10 March 1945, in which, though nearly 16 square miles were destroyed, the number killed was no larger, and fewer people were injured.
At Nagasaki, 3 days later, the city was scarcely more prepared, though vague references to the Hiroshima disaster had appeared in the newspaper of 8 August. From the Nagasaki Prefectural Report on the bombing, something of the shock of the explosion can be inferred:
The day was clear with not very much wind—an ordinary midsummer’s day. The strain of continuous air attack on the city’s population and the severity of the summer had vitiated enthusiastic air raid precautions.…
The city remained on the warning alert, but when two B-29′s were again sighted coming in the raid signal was not given immediately; the bomb was dropped at 1102 and the raid signal was given a few minutes later, at 1109. Thus only about 400 people were in the city’s tunnel shelters, which were adequate for about 30 percent of the population. When the atomic bomb exploded, an intense flash was observed first, as though a large amount of magnesium had been ignited, and the scene grew hazy with white smoke. At the same time at the center of the explosion, and a short while later in other areas, a tremendous roaring sound was heard and a crushing blast wave and intense heat were felt. The people of Nagasaki, even those who lived on the outer edge of the blast, all felt as though they had sustained a direct hit, and the whole city suffered damage such as would have resulted from direct hits everywhere by ordinary bombs.
The zero area, where the damage was most severe, was almost completely wiped out and for a short while after the explosion no reports came out of that area. People who were in comparatively damaged areas reported their condition under the impression that they had received a direct hit. If such a great amount of damage could be wreaked by a near miss, then the power of the atomic bomb is unbelievably great.
In Nagasaki, no fire storm arose, and the uneven terrain of the city confined the maximum intensity of damage to the valley over which the bomb exploded. The area of nearly complete devastation was thus much smaller; only about 1.8 square miles. Casualties were lower also; between 35,000 and 40,000 were killed, and about the same number injured. People in the tunnel shelters escaped injury, unless exposed in the entrance shaft.
The difference in the totals of destruction to lives and property at the two cities suggests the importance of the special circumstances of layout and construction of the cities, which affect the results of the bombings and must be considered in evaluating the effectiveness of the atomic bombs.…
Hiroshima before the war was the seventh largest city in Japan, with a population of over 340,000, and was the principal administrative and commercial center of the southwestern part of the country. As the headquarters of the Second Army and of the Chugoku Regional Army, it was one of the most important military command stations in Japan, the site of one of the largest military supply depots, and the foremost military shipping point for both troops and supplies. Its shipping activities had virtually ceased by the time of the attack, however, because of sinkings and the mining of the Inland Sea. It had been relatively unimportant industrially before the war, ranking only twelfth, but during the war new plants were built that increased its significance. These factories were not concentrated, but spread over the outskirts of the city; this location, we shall see, accounts for the slight industrial damage.
The impact of the atomic bomb shattered the normal fabric of community life and disrupted the organizations for handling the disaster. In the 30 percent of the population killed and the additional 30 percent seriously injured were included corresponding proportions of the civic authorities and rescue groups. A mass flight from the city took place, as persons sought safety from the conflagration and a place for shelter and food. Within 24 hours, however, people were streaming back by the thousands in search of relatives and friends and to determine the extent of their property loss. Road blocks had to be set up along all routes leading into the city, to keep curious and unauthorized people out. The bulk of the dehoused population found refuge in the surrounding countryside; within the city the food supply was short and shelter virtually nonexistent.…
The status of medical facilities and personnel dramatically illustrates the difficulties facing authorities. Of more than 200 doctors in Hiroshima before the attack, over 90 percent were casualties and only about 30 physicians were able to perform their normal duties a month after the raid. Out of 1,780 nurses, 1,654 were killed or injured. Though some stocks of supplies had been dispersed, many were destroyed. Only three out of 45 civilian hospitals could be used, and two large Army hospitals were rendered unusable. Those within 3,000 feet of ground zero were totally destroyed, and the mortality rate of the occupants was practically 100 percent.…
Fire-fighting and rescue units were equally stripped of men and equipment. Father Siemes reports that 30 hours elapsed before organized rescue parties were observed. In Hiroshima, only 16 pieces of fire-fighting equipment were available for fighting the conflagration, three of them borrowed. However, it is unlikely that any public fire department in the world, even without damage to equipment or casualties to personnel, could have prevented development of a conflagration in Hiroshima, or combatted it with success at more than a few locations along its perimeter. The total fire damage would not have been much different.
All utilities and transportation services were disrupted over varying lengths of time. In most cases, however, the demand fell off even more precipitously than the available supply, and where the service was needed it could be restored at a minimal level.…
By 1 November, the population of Hiroshima was back to 137,000. The city required complete rebuilding. The entire heart, the main administrative and commercial as well as residential section, was gone. In this area only about 50 buildings, all of reinforced concrete, remained standing. All of these suffered blast damage and all save about a dozen were almost completely gutted by fire; only 5 could be used without major repairs.…
…The official Japanese figures summed up the building destruction at 62,000 out of a total of 90,000 buildings in the urban area, or 69 percent. An additional 6,000 or 6.6 percent were severely damaged, and most of the others showed glass breakage or disturbance of roof tile. These figures show the magnitude of the problem facing the survivors.
Despite the absence of sanitation measures, no epidemics are reported to have broken out. In view of the lack of medical facilities, supplies, and personnel, and the disruption of the sanitary system, the escape from epidemics may seem surprising. The experience of other bombed cities in Germany and Japan shows that this is not an isolated case. A possible explanation may lie in the disinfecting action of the extensive fires. In later weeks, disease rates rose, but not sharply.…
At Nagasaki, the scale of destruction was greater than at Hiroshima, though the actual area destroyed was smaller because of the terrain and the point of fall of the bomb. The Nagasaki Prefectural Report describes vividly the impress of the bomb on the city and its inhabitants: Within a radius of 1 kilometer from ground zero, men and animals died almost instantaneously from the tremendous blast pressure and heat; houses and other structures were smashed, crushed and scattered; and fires broke out. The strong complex steel members of the structures of the Mitsubishi Steel Works were bent and twisted like jelly and the roofs of the reinforced concrete National Schools were crumpled and collapsed, indicating a force beyond imagination. Trees of all sizes lost their branches or were uprooted or broken off at the trunk.…
General Effects
1. Casualties.—The most striking result of the atomic bombs was the great number of casualties. The exact number of dead and injured will never be known because of the confusion after the explosions. Persons unaccounted for might have been burned beyond recognition in the falling buildings, disposed of in one of the mass cremations of the first week of recovery, or driven out of the city to die or recover without any record remaining. No sure count of even the preraid populations existed. Because of the decline in activity in the two port cities, the constant threat of incendiary raids, and the formal evacuation programs of the Government, an unknown number of the inhabitants had either drifted away from the cities or been removed according to plan. In this uncertain situation, estimates of casualties have generally ranged between 100,000 and 180,000 for Hiroshima, and between 50,000 and 100,000 for Nagasaki. The Survey believes the dead at Hiroshima to have been between 70,000 and 80,000, with an equal number injured; at Nagasaki over 35,000 dead and somewhat more than that injured seems the most plausible estimate.
Most of the immediate casualties did not differ from those caused by incendiary or high-explosive raids. The outstanding difference was the presence of radiation effects, which became unmistakable about a week after the bombing. At the time of impact, however, the causes of death and injury were flash burns, secondary effects of blast and falling debris, and burns from blazing buildings.…
The seriousness of these radiation effects may be measured by the fact that 95 percent of the traced survivors of the immediate explosion who were within 3,000 feet suffered from radiation disease.…
A plausible estimate of the importance of the various causes of death would range as follows:
Flash burns, 20 to 30 percent. Other injuries, 50 to 60 percent. Radiation sickness, 15 to 20 percent.…
Flash burns.—The flash of the explosion, which was extremely brief, emitted radiant heat travelling at the speed of light. Flash burns thus followed the explosion instantaneously. The fact that relatively few victims suffered burns of the eyeballs should not be interpreted as an indication that the radiant heat followed the flash, or that time was required to build up to maximum heat intensity. The explanation is simply that the structure of the eye is more resistant to heat than is average human skin, and near ground zero the recessed position of the eyeball offered protection from the overhead explosion. Peak temperatures lasted only momentarily.
Survivors in the two cities stated that people who were in the open directly under the explosion of the bomb were so severely burned that the skin was charred dark brown or black and that they died within a few minutes or hours.…
Because of the brief duration of the flash wave and the shielding effects of almost any objects—leaves and clothing as well as buildings—there were many interesting cases of protection. The radiant heat came in a direct line like light, so that the area burned corresponded to this directed exposure. Persons whose sides were toward the explosion often showed definite burns of both sides of the back while the hollow of the back escaped. People in buildings or houses were apparently burned only if directly exposed through the windows. The most striking instance was that of a man writing before a window. His hands were seriously burned but his exposed face and neck suffered only slight burns due to the angle of entry of the radiant heat through the window.
Flash burns were largely confined to exposed areas of the body, but on occasion would occur through varying thicknesses of clothing. Generally speaking, the thicker the clothing the more likely it was to give complete protection against flash burns. One woman was burned over the shoulder except for a T-shaped area about one-fourth inch in breadth; the T-shaped area corresponded to an increased thickness of the clothing from the seam of the garment. Other people were burned through a single thickness of kimono but were unscathed or only slightly affected underneath the lapel. In other instances, skin was burned beneath tightly fitting clothing but was unburned beneath loosely fitting portions. Finally, white or light colors reflected heat and afforded some protection; people wearing black or dark-colored clothing were more likely to be burned.
…Comparatively few instances were reported of arms or legs being torn from the body by flying debris. Another indication of the rarity of over-pressure is the scarcity of ruptured eardrums. Among 106 victims examined by the Japanese in Hiroshima on 11 and 12 August, only three showed ruptured eardrums.…
Injuries produced by falling and flying debris were much more numerous, and naturally increased in number and seriousness nearer the center of the affected area. The collapse of the buildings was sudden, so that thousands of people were pinned beneath the debris. Many were able to extricate themselves or received aid in escaping, but large numbers succumbed either to their injuries or to fire before they could be extricated. The flimsiness of Japanese residential construction should not be allowed to obscure the dangers of collapse; though the walls and partitions were light, the houses had heavy roof timbers and heavy roof tiles. Flying glass from panels also caused a large number of casualties, even up to 15,000 feet from ground zero.
The number of burns from secondary fires was slight among survivors, but it was probable that a large number of the deaths in both cities came from the burning of people caught in buildings. Eyewitness accounts agree that many fatalities occurred in this way, either immediately or as a result of the lack of care for those who did extricate themselves with serious burns. There are no references, however, to people in the streets succumbing either to heat or to carbon monoxide as they did in Tokyo or in Hamburg, Germany. A few burns resulted from clothing set afire by the flash wave, but in most cases people were able to beat out such fires without serious injury to the skin.
Radiation disease.—The radiation effects upon survivors resulted from the gamma rays liberated by the fission process rather than from induced radio-activity or the lingering radio-activity of deposits of primary fission products. Both at Nagasaki and at Hiroshima, pockets of radio-activity have been detected where fission products were directly deposited, but the degree of activity in these areas was insufficient to produce casualties. Similarly, induced radio-activity from the interaction of neutrons with matter caused no authenticated fatalities. But the effects of gamma rays—here used in a general sense to include all penetrating high-frequency radiations and neutrons that caused injury—are well established, even though the Allies had no observers in the affected areas for several weeks after the explosions.
Our understanding of radiation casualties is not complete. In part the deficiency is in our basic knowledge of how radiation affects animal tissue. In the words of Dr. Robert Stone of the Manhattan Project, ‘The fundamental mechanism of the action of radiation on living tissues has not been understood.…”
According to the Japanese, those individuals very near the center of the explosion but not affected by flash burns or secondary injuries became ill within 2 or 3 days. Bloody diarrhea followed, and the victims expired, some within 2 to 3 days after the onset and the majority within a week. Autopsies showed remarkable changes in the blood picture—almost complete absence of white blood cells, and deterioration of bone marrow. Mucous membranes of the throat, lungs, stomach, and the intestines showed acute inflammation.
The majority of the radiation cases, who were at greater distances, did not show severe symptoms until 1 to 4 weeks after the explosion, though many felt weak and listless on the following day. After a day or two of mild nausea and vomiting, the appetite improved and the person felt quite well until symptoms reappeared at a later date.… Within 12 to 48 hours, fever became evident. In many instances it reached only 100° Fahrenheit and remained for only a few days. In other cases, the temperature went as high as 104° or 106° Fahrenheit. The degree of fever apparently had a direct relation to the degree of exposure to radiation. Once developed, the fever was usually well sustained, and in those cases terminating fatally it continued high until the end. If the fever subsided, the patient usually showed a rapid disappearance of other symptoms and soon regained his feeling of good health. The other symptoms commonly seen were shortage of white corpuscles, loss of hair, inflammation and gangrene of the gums, inflammation of the mouth and pharynx, ulceration of the lower gastro-intestinal tract, small livid spots (petechiae) resulting from escape of blood into the tissues of the skin or mucous membrane, and larger hemorrhages of gums, nose and skin.…
A decrease in the number of white blood corpuscles in the circulating blood appears to have been a constant accompaniment of radiation disease, even existing in some milder cases without other radiation effects. The degree of leukopenia was probably the most accurate index of the amount of radiation a person received. The normal white blood count averages 5,000 to 7,000: leukopenia is indicated by a count of 4,000 or less. The white blood count in the more severe cases ranged from 1,500 to 0, with almost entire disappearance of the bone marrow. The moderately severe cases showed evidence of degeneration of bone marrow and total white blood counts of 1,500 to 3,000. The milder cases showed white blood counts of 3,000 to 4,000 with more minor degeneration changes in the bone marrow. The changes in the system for forming red blood corpuscles developed later, but were equally severe.
Radiation clearly affected reproduction, though the extent has not been determined. Sterility has been a common finding throughout Japan, especially under the conditions of the last 2 years, but there are signs of an increase in the Hiroshima and Nagasaki areas to be attributed to the radiation. Sperm counts done in Hiroshima under American supervision revealed low sperm counts or complete aspermia for as long as 3 months afterward in males who were within 5,000 feet of the center of the explosion. Cases dying of radiation disease showed clear effects on spermatogenesis. Study of sections of ovaries from autopsied radiation victims has not yet been completed. The effects of the bomb on pregnant women are marked, however. Of women in various stages of pregnancy who were within 3,000 feet of ground zero, all known cases have had miscarriages. Even up to 6,500 feet they have had miscarriages or premature infants who died shortly after birth. In the group between 6,500 and 10,000 feet, about one-third have given birth to apparently normal children. Two months after the explosion, the city’s total incidence of miscarriages, abortions, and premature births was 27 percent as compared with a normal rate of 6 percent. Since other factors than radiation contributed to this increased rate, a period of years will be required to learn the ultimate effects of mass radiation upon reproduction.…
Unfortunately, no exact definition of the killing power of radiation can yet be given, nor a satisfactory account of the sort and thickness of concrete or earth that will shield people.… In the meanwhile the awesome lethal effects of the atomic bomb and the insidious additional peril of the gamma rays speak for themselves.
There is reason to believe that if the effects of blast and fire had been entirely absent from the bombing, the number of deaths among people within a radius of one-half mile from ground zero would have been almost as great as the actual figures and the deaths among those within 1 mile would have been only slightly less. The principal difference would have been in the time of the deaths. Instead of being killed outright as were most of these victims, they would have survived for a few days or even 3 or 4 weeks, only to die eventually of radiation disease.…
2. Morale.—As might be expected, the primary reaction to the bomb was fear—uncontrolled terror, strengthened by the sheer horror of the destruction and suffering witnessed and experienced by the survivors.…
The behavior of the living immediately after the bombings, as described earlier, clearly shows the state of shock that hindered rescue efforts. A Nagasaki survivor illustrates succinctly the mood of survivors: …I was working at the office. I was talking to a friend at the window. I saw the whole city in a red flame, then I ducked. The pieces of the glass hit my back and face. My dress was torn off by the glass. Then I got up and ran to the mountain where the good shelter was.
The two typical impulses were those: Aimless, even hysterical activity or flight from the city to shelter and food.
The accentuated effect of these bombs came not only from the surprise and their crushing power, but also from the feeling of security among the inhabitants of the two cities before the attacks. Though Nagasaki had undergone five raids in the previous year, they had not been heavy, and Hiroshima had gone almost untouched until the morning of 6 August 1945. In both cities many people felt that they would be spared, and the various rumors in circulation supporting such feeling covered a wide range of wishful thoughts. There were so many Christians there, many Japanese-Americans came from Hiroshima, the city was a famous beauty spot—these and other even more fantastic reasons encouraged hopes. Other people felt vaguely that their city was being saved for “something big,” however.…
3. The Japanese decision to surrender.—The further question of the effects of the bombs on the morale of the Japanese leaders and their decision to abandon the war is tied up with other factors. The atomic bomb had more effect on the thinking of Government leaders than on the morale of the rank and file of civilians outside of the target areas. It cannot be said, however, that the atomic bomb convinced the leaders who effected the peace of the necessity of surrender. The decision to seek ways and means to terminate the war, influenced in part by knowledge of the low state of popular morale, had been taken in May 1945 by the Supreme War Guidance Council.
As early as the spring of 1944, a group of former prime ministers and others close to the Emperor had been making efforts toward bringing the war to an end.…
Thus the problem facing the peace leaders in the Government was to bring about a surrender despite the hesitation of the War Minister and the opposition of the Army and Navy chiefs of staff. This had to be done, moreover, without precipitating counter measures by the Army which would eliminate the entire peace group. This was done ultimately by bringing the Emperor actively into the decision to accept the Potsdam terms. So long as the Emperor openly supported such a policy and could be presented to the country as doing so, the military, which had fostered and lived on the idea of complete obedience to the Emperor, could not effectively rebel.
A preliminary step in this direction had been taken at the Imperial Conference on 26 June. At this meeting, the Emperor, taking an active part despite his custom to the contrary, stated that he desired the development of a plan to end the war as well as one to defend the home islands. This was followed by a renewal of earlier efforts to get the Soviet Union to intercede with the United States, which were effectively answered by the Potsdam Declaration on 26 July and the Russian declaration of war on 9 August.
The atomic bombings considerably speeded up these political maneuverings within the government. This in itself was partly a morale effect, since there is ample evidence that members of the Cabinet were worried by the prospect of further atomic bombings, especially on the remains of Tokyo. The bombs did not convince the military that defense of the home islands was impossible, if their behavior in Government councils is adequate testimony. It did permit the Government to say, however, that no army without the weapon could possibly resist an enemy who had it, thus saving ‘face” for the Army leaders and not reflecting on the competence of Japanese industrialists or the valor of the Japanese soldier. In the Supreme War Guidance Council voting remained divided, with the war minister and the two chiefs of staff unwilling to accept unconditional surrender. There seems little doubt, however, that the bombing of Hiroshima and Nagasaki weakened their inclination to oppose the peace group.
The peace effort culminated in an Imperial conference held on the night of 9 August and continued into the early hours of 10 August, for which the stage was set by the atomic bomb and the Russian war declaration. At this meeting the Emperor, again breaking his customary silence, stated specifically that he wanted acceptance of the Potsdam terms.
A quip was current in high Government circles at this time that the atomic bomb was the real Kamikaze, since it saved Japan from further useless slaughter and destruction. It is apparent that in the atomic bomb the Japanese found the opportunity which they had sought, to break the existing deadlock within the Government over acceptance of the Potsdam terms.
The Effects of the Atomic Bombs as presented by United States Strategic Bombing Survey
Source: Articles from Bibliobase edited by Michael A. Bellesiles. Copyright © 1998 by Houghton Mifflin Company.
