Chapter IV

A. The Danger

The Survey's investigators, as they proceeded about their study, sound an insistent question framing itself in their minds: "What if the target for the bomb had been an American City?" True, the primary mission of the Survey was to ascertain the facts just summarized. But conclusions as to the meaning of those facts, for citizens of the United States, forced themselves almost inescapable on the men who examined thoughtfully the remains of Hiroshima and Nagasaki. These conclusions have a different sort of validity from the measurable and ponderable facts of preceding sections, and therefore they are presented separately. They are not the least important part of this report, however, and they are stated with no less conviction.

No two cities, whether in Japan or the United States, are exactly alike. But the differences in terrain, layout and zoning, density, and type of construction can be allowed for one by one; when that is done, comparisons become possible. The most striking difference between American and Japanese cities is in residential districts: what happened to typical Japanese homes is not directly applicable to American residential districts. But in Japanese cities were many brick and wood frame buildings of Western or similar design and of good workmanship. It was the opinion of the Survey's engineers, with their professional familiarity with American buildings, that these Japanese buildings reacted to the bomb much as typical American buildings would have. And these buildings were exceedingly vulnerable: multi-story brick buildings with load-bearing walls were destroyed or seriously damaged over an area of 3.6 square miles at Hiroshima, while similar one-story brick buildings were destroyed or seriously damaged within an area of 6 square miles. Wood frame buildings built as industrial or commercial shops suffered similar damage in an area of over 8 miles, while Japanese residences were destroyed or seriously damaged within an area of 6 square miles. This was at Hiroshima, where the less powerful bomb was used!

These figures indicate what would happen to typical wood, brick, and stucco structures in American cities. Modern reinforced concrete and steel frame buildings would fare better here--as they did in Japan. But the following table shows how American cities are built, and how few buildings are of blast-resistant construction.

City Types of structures by exterior material (United States cities)
Wood Brick Stucco Other
New York 591,319 236,879 299,482 41,661 13,297
Washington 156,359 48,971 95,939 5,764 5,685
Chicago 382,628 131,148 238,959 5,797 6,724
Detroit 267,677 165,488 94,333 1,923 5,933
San Francisco 105,180 61,172 2,334 40,902 722

The overwhelming bulk of the buildings in American cities could not stand up against an atomic bomb bursting a mile or a mile and a half from them.

And the people? We must not too readily discount the casualty rate because of the teeming populations of congested Japanese cities. American cities, too, have their crowded slums, and in addition tend to build vertically so that the density of the population is high in a given area even though each apartment dweller may have more living space than his Japanese equivalent.

Most of the population densities in this table are merely averages for people within a city limits. Most meaningful, therefore, are the figures for the central areas of Hiroshima and Nagasaki, and for the boroughs of New York. The casualty rates at Hiroshima and Nagasaki, applied to the massed inhabitants of Manhattan, Brooklyn, and the Bronx, yield a grim conclusion. These casualty rates, it must never be forgotten, result from the first atomic bombs to be used and from bombs burst


DAMAGE TO MACHINE TOOLS was usually indirect. At the Mitsubishi Steel and Arms Works, 4,200 feet from ground zero at Nagasaki, many closely packed machines escaped serious damage from collapsing roof trusses, but were exposed to the weather. Other machines were torn from their foundations by collapsing steel members.


a considerable distances above the ground. Improved bombs, perhaps detonated more effectively, may well prove still more deadly.

B. What Can We Do About It

The danger is real--of that, the Survey's findings leave no doubt. Scattered through those findings, at the same time, are the clues to the measures that can be taken to cut down potential losses of lives and property. These measures must be taken or initiated now, if their cost is not to be prohibitive. But if a policy is laid down, well in advance of any crisis, it will enable timely decentralization of industrial and medical facilities, construction or blueprinting of shelters, and preparation for life-saving evacuation programs. The almost unprotected, completely surprised cities of Japan suffered maximum losses from atomic bomb attack. If we recognize in advance the possible danger and act to forestall it, we shall at worst suffer minimum casualties and disruption.

Since modern science can be marshalled for the defense as well as the attack, there is reason to hope that protective weapons and techniques will be improved. Even protective devices and vigilance, however, cannot be perfect guards against surprise or initial attack, or against the unlimited choices of targets offered an enemy through the range and speed of modern weapons. In our planning for the future, if we are realistic, we will prepare to minimize the destructiveness of such attacks, and so organize the economic and administrative life of the Nation that no single or small group of successful attacks can paralyze the national organism. The foregoing description of the effectiveness of the atomic bomb has shown clearly that, despite its awesome power, it has limits of which wise planning will take prompt advantage.

1. Shelters.--

The most instructive fact at Nagasaki was the survival, even when near ground zero, of the few hundred people who were properly placed in the tunnel shelters. Carefully built shelters, though unoccupied, stood up well in both cities. Without question, shelters can protect those who get to them against anything but a direct hit. Adequate warning will assure that a maximum number get to shelters.

Analysis of the protection of survivors within a few hundred feet of ground zero shows that shielding is possible even against gamma rays. At Hiroshima, for example, persons in a concrete building 3,600 feet from ground zero showed no clinical effects from gamma radiation, but those protected only by wooden buildings at a similar distance suffered from radiation disease. The necessary thickness varies with the substance and with the distance from the point of detonation. Adequate shelters can be built which will reduce substantially the casualties from radiation.

Men arriving at Hiroshima and Nagasaki have been constantly impressed by the shells of reinforced concrete buildings still rising above the rubble of brick and stone or the ashes of wooden buildings. In most cases gutted by fire or stripped or partitions and interior trim, these buildings have a double lesson for us. They show, first, that it is possible without excessive expense to erect buildings which will satisfactorily protect their contents at distances of about 2,000 feet or more from a bomb of the types so far employed. Construction of such buildings would be similar to earthquake resistant construction, which California experience indicates would cost about 10 percent to 15 percent more than conventional construction. Even against more powerful bombs or against near misses, such construction would diminish damage. Second, the internal damage illustrates the danger from interior details and construction which result in fore or flying debris in otherwise sound buildings. The elimination of combustible interiors and the provision of full-masonry partition


HEAVY ELECTRICAL EQUIPMENT such as this turbogenerator at Minami Sendamachi substation 7,700 feet from ground zero at Hiroshima, often survived the explosion.

NAGASAKI. Steel-framed building about 4,000 feet south of ground zero in Mitsubishi Steel and Arms Works distorted to grotesque shape by blast of bomb.


NAGASAKI SHELTERS. Tunnel shelters in the hillside, such as the ones pictured (very close to ground zero), protected the few occupants from blast, heat, and radiation.

HIROSHIMA EARTH-AND-POLE AIR-RAID SHELTER. This simple shelter is undamaged by fire and blast 5,000 feet northeast of ground zero, though surrounding buildings have been destroyed (Japanese photo, 10 August 1945).


walls, fire-resistive stair and elevator enclosures, and fire division walls would localize fires. Avoidance of glass, tile, or lath and plaster on wood stud would cut down damage from flying debris. The studies of the Physical Damage Division of the Survey support such recommendations and include many others.

The survival of sheltered sections of Nagasaki suggests forcefully the use that can be made of irregular terrain. Uneven ground reduces the spread and uniformity of blast effect. Terrain features such as rivers and parks afford natural firebreaks and avenues of escape.

2. Decentralization.--

Hiroshima and Nagasaki were chosen as targets because of their concentration of activities and population. The population density of 45,000 or more per square mile of built-up area explains in part the high casualty rate. Significant therefore is the fact that deaths at Nagasaki, despite the greater population density, were only one-half those at Hiroshima : the difference can be assigned in the main to the separation of the dispersed built-up pockets at Nagasaki, in contrast to the uniform concentration of the inhabitants in the heart of Hiroshima. The Nagasaki bomb thus dissipated much of its energy against hills, water, or unoccupied areas, while the Hiroshima bomb achieved almost optimum effect.

The fate of industries in both cities again illustrates the value of decentralization. All major factories in Hiroshima were on the Periphery of the city--and escaped serious damage; at Nagasaki, plants and dockyards at the southern end of the city were left intact, but those in the valley where the bomb exploded were seriously damaged. So spread out were the industries in both cities that no single bomb could have been significantly more effective than the two actually dropped.

Medical facilities, crowded into the heart of the city rather than evenly spread through it, were crippled or wiped out by the explosion. Only the previous removal of some stocks of medical supplies from Hiroshima to outlying communities, and the bringing in of aid, enabled the limited medical attention of the first few days.

These results underline those in conventional area raids in Germany, where frequently the heart of a city was devastated while peripheral industries continued to produce and where (particularly in Hamburg) destruction of medical facilities just at the time of greatest need hampered care of wounded.

The similar peril of American cities and the extent to which wise zoning has diminished it differ from city to city. Though a reshaping and partial dispersal of the national centers of activity are drastic and difficult measures, they represent a social and military ideal toward which very practical steps can be taken once the policy has been laid down. In the location of plants, administrative headquarters, and hospitals particularly, the value of decentralization is obvious, and can be obtained cheaply if the need is foreseen. For example, by wise selection of dispersed sites, the present hospital building program of the Veterans' Administration could be made to lessen our congestion without additional cost.

Reserve stocks of critical materials and of such products as medical supplies should be kept on hand. This principle of maintaining reserves applies also to the capital equipment of the country. Key producing areas must not come from processing plants of barely adequate capacity. Production of essential manufactured goods--civilian and military--must not be confined to a few or to geographically centralized plants. And the various regions of the country should be encouraged to approach balanced economic development as closely as is naturally possible. An enemy viewing our national economy must not find bottlenecks which use of the atomic bomb could choke off to throttle our productive capacity.

3. Civilian Defense

Because the scale of disaster would be certain to overwhelm the locality in which it occurs, mutual assistance organized on a national level is essential. Such national organization is by no means inconsistent with decentralization; indeed, it will be aided by the existence of the maximum number of nearly self-sustaining regions whose joint support it can coordinate. In addition, highly trained mobile units skilled in and equipped for fire fighting, rescue work, and clearance and repair should be trained for an emergency which disrupts local organization and exceeds its capability for control.

Most important, a national civilian defense organization can prepare now the plans for necessary steps in case of crisis. Two complementary programs which should be worked out in advance are those for evacuation of unnecessary inhabitants


THIS STEEL FRAME BUILDING, 2,000 feet from ground zero at Hiroshima, had its first-story columns buckle away from the blast, dropping the second story to the ground. Combustibles were destroyed by fire.

COLLAPSE OF REINFORCED CONCRETE BUILDING. Chugoku Coal Distrubtion Control Co., 700 feet from ground zero at Hiroshima.


from threatened urban areas, and for rapid erection of adequate shelters for people who must remain.

4. Active Defense.--

Protective measures can substantially reduce the degree of devastation from an atomic bomb and the rate of casualties. Yet if the possibility of atomic attack on us is accepted, we must accept also the fact that no defensive measures alone can long protect us. At best they can minimize our losses and preserve the functioning of the national community through initial or continuing partial attack. Against full and sustained attacks they would be ineffectual palliatives.

As defensive weapons, atomic bombs are useful primarily as warnings, as threats of retaliation which will restrain a potential aggressor from their use as from the use of poison gas or biological warfare. The mission of active defense, as of passive defense, is thus to prevent the surprise use of the atomic bomb from being decisive. A wise military establishment will make sure--by dispersal, concealment, protection, and constant readiness of its forces--that no single blow or series of blows from an enemy can cripple its ability to strike back in the same way or to repel accompanying attacks from other air, ground, or sea forces. The measures to enable this unrelaxing state of readiness are not new; only their urgency is increased. Particularly is this true of the intelligence activities on which informed decisions and timely actions depend.

The need for research is not limited to atomic energy itself, but is equally important in propellants, detection devices, and other techniques of countering and of delivering atomic weapons. Also imperative is the testing of the weapon's potentialities under varying conditions. The coming Operation Crossroads, for example, will give valuable data for defining more precisely what is already known about the atomic bomb's effectiveness when air-burst; more valuable, however, will be tests under new conditions, to provide sure information about detonations at water level or under water, as well as underground. While prediction of effects under differing conditions of detonation may have a high degree of probability, verified knowledge is a much better basis for military planning.

5. Conclusion.--

One further measure of safety must accompany the others. To avoid destruction, the surest way is to avoid war. This was the Survey's recommendation after viewing the rubble of German cities, and it holds equally true whether one remembers the ashes of Hiroshima or considers the vulnerability of American cities.

Our national policy has consistently had as one of its basic principles the maintenance of peace. Based on our ideals of justice and of peaceful development of our resources, this disinterested policy has been reinforced by our clear lack of anything to gain from war--even in victory. No more forceful arguments for peace and for the international machinery of peace than the sight of the devastation of Hiroshima and Nagasaki have ever been devised. As the developer and exploiter of this ominous weapon, our nation has a responsibility, which no American should shirk, to lead in establishing and implementing the international guarantees and controls which will prevent its future use.


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