In considering the devastation in the two cities, it should be
remembered that the cities' differences in shape and topography
resulted in great differences in the damages. Hiroshima was all on
low, flat ground, and was roughly circular in shape; Nagasaki was much
cut up by hills and mountain spurs, with no regularity to its shape.
In Hiroshima almost everything up to about one mile from X was
completely destroyed, except for a small number (about 50) of heavily
reinforced concrete buildings, most of which were specially designed to
withstand earthquake shock, which were not collapsed by the blast; most
of these buildings had their interiors completely gutted, and all
windows, doors, sashes, and frames ripped out. In Nagasaki, nearly
everything within 1/2 mile of the explosion was destroyed, including
heavy structures. All Japanese homes were destroyed within 1 1/2 miles
from X.
Underground air raid shelters with earth cover roofs immediately below
the explosion had their roofs caved in; but beyond 1/2 mile from X they
suffered no damage.
In Nagasaki, 1500 feet from X high quality steel frame buildings were
not completely collapsed, but the entire buildings suffered mass
distortion and all panels and roofs were blown in.
In Nagasaki, 2,000 feet from X, reinforced concrete buildings with 10"
walls and 6" floors were collapsed; reinforced concrete buildings with
4" walls and roofs were standing but were badly damaged. At 2,000 feet
some 9" concrete walls were completely destroyed.
In Nagasaki, 3,500 feet from X, church buildings with 18" brick walls
were completely destroyed. 12" brick walls were severely cracked as
far as 5,000 feet.
In Hiroshima, 4,400 feet from X, multi-story brick buildings were
completely demolished. In Nagasaki, similar buildings were destroyed
to 5,300 feet.
In Hiroshima, roof tiles were bubbled (melted) by the flash heat out to
4,000 feet from X; in Nagasaki, the same effect was observed to 6,500
feet.
In Hiroshima, steel frame buildings were destroyed 4,200 feet from X,
and to 4,800 feet in Nagasaki.
In both cities, the mass distortion of large steel buildings was
observed out to 4,500 feet from X.
In Nagasaki, reinforced concrete smoke stacks with 8" walls, specially
designed to withstand earthquake shocks, were overturned up to 4,000
feet from X.
In Hiroshima, steel frame buildings suffered severe structural damage
up to 5,700 feet from X, and in Nagasaki the same damage was sustained
as far as 6,000 feet.
In Nagasaki, 9" brick walls were heavily cracked to 5,000 feet, were
moderately cracked to 6,000 feet, and slightly cracked to 8,000 feet.
In both cities, light concrete buildings collapsed out to 4,700 feet.
In Hiroshima, multi-story brick buildings suffered structural damage up
to 6,600 feet, and in Nagasaki up to 6,500 feet from X.
In both cities overhead electric installations were destroyed up to
5,500 feet; and trolley cars were destroyed up to 5,500 feet, and
damaged to 10,500 feet.
Flash ignition of dry, combustible material was observed as far as
6,400 feet from X in Hiroshima, and in Nagasaki as far as 10,000 feet
from X.
Severe damage to gas holders occured out to 6,500 feet in both cities.
All Japanese homes were seriously damaged up to 6,500 feet in
Hiroshima, and to 8,000 feet in Nagasaki. Most Japanese homes were
damaged up to 8,000 feet in Hiroshima and 10,500 feet in Nagasaki.
The hillsides in Nagasaki were scorched by the flash radiation of heat
as far as 8,000 feet from X; this scorching gave the hillsides the
appearance of premature autumn.
In Nagasaki, very heavy plaster damage was observed in many buildings
up to 9,000 feet; moderate damage was sustained as far as 12,000 feet,
and light damage up to 15,000 feet.
The flash charring of wooden telegraph poles was observed up to 9,500
feet from X in Hiroshima, and to 11,000 feet in Nagasaki; some reports
indicate flash burns as far as 13,000 feet from X in both places.
Severe displacement of roof tiles was observed up to 8,000 feet in
Hiroshima, and to 10,000 feet in Nagasaki.
In Nagasaki, very heavy damage to window frames and doors was observed
up to 8,000 feet, and light damage up to 12,000 feet.
Roofs and wall coverings on steel frame buildings were destroyed out to
11,000 feet.
Although the sources of many fires were difficult to trace accurately,
it is believed that fires were started by primary heat radiation as far
as 15,000 feet from X.
Roof damage extended as far as 16,000 feet from X in Hiroshima and in
Nagasaki.
The actual collapse of buildings was observed at the extreme range of
23,000 feet from X in Nagasaki.
Although complete window damage was observed only up to 12,000 feet
from X, some window damage occurred in Nagasaki up to 40,000 feet, and
actual breakage of glass occured up to 60,000 feet.
Heavy fire damage was sustained in a circular area in Hiroshima with a
mean radius of about 6,000 feet and a maximum radius of about 11,000
feet; similar heavy damage occured in Nagasaki south of X up to 10,000
feet, where it was stopped on a river course.
In Hiroshima over 60,000 of 90,000 buildings were destroyed or severely
damaged by the atomic bomb; this figure represents over 67% of the
city's structures.
In Nagasaki 14,000 or 27% of 52,000 residences were completely
destroyed and 5,400, or 10% were half destroyed. Only 12% remained
undamaged. This destruction was limited by the layout of the city.
The following is a summary of the damage to buildings in Nagasaki as
determined from a ground survey made by the Japanese:
Destruction of Buildings and Houses Number Percentage
(Compiled by Nagasaki Municipality)
Total in Nagasaki (before atomic explosion) 50,000 100.0
Blasted (not burned) 2,652 5.3
Blasted and burned 11,494 23.0
Blasted and/or burned 14,146 28.3
Partially burned or blasted 5,441 10.9
Total buildings and houses destroyed 19,587 39.2
Undamaged 30,413 60.8
In Hiroshima, all utilities and transportation services were disrupted
for varying lengths of time. In general however services were restored
about as rapidly as they could be used by the depleted population.
Through railroad service was in order in Hiroshima on 8 August, and
electric power was available in most of the surviving parts on 7
August, the day after the bombing. The reservoir of the city was not
damaged, being nearly 2 miles from X. However, 70,000 breaks in water
pipes in buildings and dwellings were caused by the blast and fire
effects. Rolling transportation suffered extensive damage. The damage
to railroad tracks, and roads was comparatively small, however. The
electric power transmission and distribution systems were badly
wrecked. The telephone system was approximately 80% damaged, and no
service was restored until 15 August.
Despite the customary Japanese lack of attention to sanitation
measures, no major epidemic broke out in the bombed cities. Although
the conditions following the bombings makes this fact seem surprising,
the experience of other bombed cities in both Germany and Japan show
Hiroshima and Nagasaki not to be isolated cases.
The atomic explosion over Nagasaki affected an over-all area of
approximately 42.9 square miles of which about 8.5 square miles were
water and only about 9.8 square miles were built up, the remainder
being partially settled. Approximately 36% of the built up areas were
seriously damaged. The area most severely damaged had an average
radius of about 1 mile, and covered about 2.9 square miles of which 2.4
were built up.
In Nagasaki, buildings with structural steel frames, principally the
Mitsubishi Plant as far as 6,000 feet from X were severely damaged;
these buildings were typical of wartime mill construction in America
and Great Britain, except that some of the frames were somewhat less
substantial. The damage consisted of windows broken out (100%), steel
sashes ripped out or bent, corrugated metal or corrugated asbestos
roofs and sidings ripped off, roofs bent or destroyed, roof trusses
collapsed, columns bent and cracked and concrete foundations for
columns rotated. Damage to buildings with structural steel frames was
more severe where the buildings received the effect of the blast on
their sides than where the blast hit the ends of buildings, because the
buildings had more stiffness (resistance to negative moment at the top
of columns) in a longitudinal direction. Many of the lightly
constructed steel frame buildings collapsed completely while some of
the heavily constructed (to carry the weight of heavy cranes and loads)
were stripped of roof and siding, but the frames were only partially
injured.
The next most seriously damaged area in Nagasaki lies outside the 2.9
square miles just described, and embraces approximately 4.2 square
miles of which 29% was built up. The damage from blast and fire was
moderate here, but in some sections (portions of main business
districts) many secondary fires started and spread rapidly, resulting
in about as much over-all destruction as in areas much closer to X.
An area of partial damage by blast and fire lies just outside the one
just described and comprises approximately 35.8 square miles. Of this
area, roughly 1/6th was built up and 1/4th was water. The extent of
damage varied from serious (severe damage to roofs and windows in the
main business section of Nagasaki, 2.5 miles from X), to minor (broken
or occasionally broken windows at a distance of 7 miles southeast of X).
As intended, the bomb was exploded at an almost ideal location over
Nagasaki to do the maximum damage to industry, including the Mitsubishi
Steel and Arms Works, the Mitsubishi-Urakami Ordnance Works (Torpedo
Works), and numerous factories, factory training schools, and other
industrial establishments, with a minimum destruction of dwellings and
consequently, a minimum amount of casualties. Had the bomb been
dropped farther south, the Mitsubishi-Urakami Ordnance Works would not
have been so severely damaged, but the main business and residential
districts of Nagasaki would have sustained much greater damage
casualties.
Calculations show that the structural steel and reinforced concrete
frames which survived the blast fairly close to X could not have
withstood the estimated peak pressures developed against the total
areas presented by the sides and roof of the buildings. The survival
of these frames is explained by the fact that they were not actually
required to withstand the peak pressure because the windows were
quickly knocked out and roof and siding stripped off thereby reducing
total area and relieving the pressure. While this saved the building
frame, it permitted severe damage to building interior and contents,
and injuries to the building occupants. Buildings without large panel
openings through which the pressure could dissipate were completely
crushed, even when their frames were as strong as those which survived.
The damage sustained by reinforced concrete buildings depended both on
the proximity to X and the type and strength of the reinforced concrete
construction. Some of the buildings with reinforced concrete frames
also had reinforced concrete walls, ceilings, and partitions, while
others had brick or concrete tile walls covered either with plaster or
ornamental stone, with partitions of metal, glass, and plaster. With
the exception of the Nagasaki Medical School and Hospital group, which
was designed to withstand earthquakes and was therefore of heavier
construction than most American structures, most of the reinforced
concrete structures could be classified only as fair, with concrete of
low strength and density, with many of the columns, beams, and slabs
underdesigned and improperly reinforced. These facts account for some
of the structural failures which occured.
In general, the atomic bomb explosion damaged all windows and ripped
out, bent, or twisted most of the steel window or door sashes, ripped
doors from hinges, damaged all suspended wood, metal, and plaster
ceilings. The blast concussion also caused great damage to equipment
by tumbling and battering. Fires generally of secondary origin
consumed practically all combustible material, caused plaster to crack
off, burned all wooden trim, stair covering, wooden frames of wooden
suspended ceilings, beds, mattresses, and mats, and fused glass, ruined
all equipment not already destroyed by the blast, ruined all electrical
wiring, plumbing, and caused spalling of concrete columns and beams in
many of the rooms.
Almost without exception masonry buildings of either brick or stone
within the effective limits of the blast were severely damaged so that
most of them were flattened or reduced to rubble. The wreckage of a
church, approximately 1,800 feet east of X in Nagasaki, was one of the
few masonry buildings still recognizable and only portions of the walls
of this structure were left standing. These walls were extremely thick
(about 2 feet). The two domes of the church had reinforced concrete
frames and although they were toppled, they held together as units.
Practically every wooden building or building with timber frame within
2.0 miles of X was either completely destroyed or very seriously
damaged, and significant damage in Nagasaki resulted as far as 3 miles
from X. Nearly all such buildings collapsed and a very large number
were consumed by fire.
A reference to the various photographs depicting damage shows that
although most of the buildings within the effective limits of the blast
were totally destroyed or severely damaged, a large number of chimneys
even close to X were left standing, apparently uninjured by the
concussion. One explanation is that concrete chimneys are
approximately cylindrical in shape and consequently offer much less
wind resistance than flat surfaces such as buildings. Another
explanation is that since the cities were subject to typhoons the more
modern chimneys were probably designed to withstand winds of high
velocity. It is also probable that most of the recently constructed
chimneys as well as the more modern buildings were constructed to
withstand the acceleration of rather severe earthquakes. Since the
bombs were exploded high in the air, chimneys relatively close to X
were subjected to more of a downward than a lateral pressure, and
consequently the overturning moment was much less than might have been
anticipated.
Although the blast damaged many bridges to some extent, bridge damage
was on the whole slight in comparison to that suffered by buildings.
The damage varied from only damaged railings to complete destruction of
the superstructure. Some of the bridges were wrecked and the spans
were shoved off their piers and into the river bed below by the force
of the blast. Others, particularly steel plate girder bridges, were
badly buckled by the blast pressure. None of the failures observed
could be attributed to inadequate design or structural weaknesses.
The roads, and railroad and street railway trackage sustained
practically no primary damage as a result of the explosion. Most of
the damage to railroads occurred from secondary causes, such as fires
and damage to bridges or other structures. Rolling stock, as well as
automobiles, trolleys, and buses were destroyed and burned up to a
considerable distance from X. Streets were impassable for awhile
because of the debris, but they were not damaged. The height of the
bomb explosion probably explains the absence of direct damage to
railroads and roads.
A large part of the electric supply was interrupted by the bomb blast
chiefly through damage to electric substations and overhead
transmission systems. Both gas works in Nagasaki were severely damaged
by the bomb. These works would have required 6-7 months to get into
operation. In addition to the damage sustained by the electrical and
gas systems, severe damage to the water supply system was reported by
the Japanese government; the chief damage was a number of breaks in the
large water mains and in almost all of the distributing pipes in the
areas which were affected by the blast. Nagasaki was still suffering
from a water shortage inside the city six weeks after the atomic attack.
The Nagasaki Prefectural report describes vividly the effects of the
bomb on the city and its inhabitants:
"Within a radius of 1 kilometer from X, men and animals died almost
instantaneously and outside a radius of 1 kilometer and within a radius
of 2 kilometers from X, some men and animals died instantly from the
great blast and heat but the great majority were seriously or
superficially injured. Houses and other structures were completely
destroyed while fires broke out everywhere. Trees were uprooted and
withered by the heat.
"Outside a radius of 2 kilometers and within a radius of 4 kilometers
from X, men and animals suffered various degrees of injury from window
glass and other fragments scattered about by the blast and many were
burned by the intense heat. Dwellings and other structures were half
damaged by blast.
"Outside a radius of 4 kilometers and within a radius of 8 kilometers
living creatures were injured by materials blown about by the blast;
the majority were only superficially wounded. Houses were only half or
partially damaged."
The British Mission to Japan interpreted their observations of the
destruction of buildings to apply to similar construction of their own
as follows:
A similar bomb exploding in a similar fashion would produce the
following effects on normal British houses:
Up to 1,000 yards from X it would cause complete collapse.
Up to 1 mile from X it would damage the houses beyond repair.
Up to 1.5 miles from X it would render them uninhabitable without
extensive repair, particularly to roof timbers.
Up to 2.5 miles from X it would render them uninhabitable until
first-aid repairs had been carried out.
The fire damage in both cities was tremendous, but was more complete in
Hiroshima than in Nagasaki. The effect of the fires was to change
profoundly the appearance of the city and to leave the central part
bare, except for some reinforced concrete and steel frames and objects
such as safes, chimney stacks, and pieces of twisted sheet metal. The
fire damage resulted more from the properties of the cities themselves
than from those of the bombs.
The conflagration in Hiroshima caused high winds to spring up as air
was drawn in toward the center of the burning area, creating a "fire
storm". The wind velocity in the city had been less than 5 miles per
hour before the bombing, but the fire-wind attained a velocity of 30-40
miles per hour. These great winds restricted the perimeter of the fire
but greatly added to the damage of the conflagration within the
perimeter and caused the deaths of many persons who might otherwise
have escaped. In Nagasaki, very severe damage was caused by fires, but
no extensive "fire storm" engulfed the city. In both cities, some of
the fires close to X were no doubt started by the ignition of highly
combustible material such as paper, straw, and dry cloth, upon the
instantaneous radiation of heat from the nuclear explosion. The
presence of large amounts of unburnt combustible materials near X,
however, indicated that even though the heat of the blast was very
intense, its duration was insufficient to raise the temperature of many
materials to the kindling point except in cases where conditions were
ideal. The majority of the fires were of secondary origin starting
from the usual electrical short-circuits, broken gas lines, overturned
stoves, open fires, charcoal braziers, lamps, etc., following collapse
or serious damage from the direct blast.
Fire fighting and rescue units were stripped of men and equipment.
Almost 30 hours elapsed before any rescue parties were observable. In
Hiroshima only a handful of fire engines were available for fighting
the ensuing fires, and none of these were of first class type. In any
case, however, it is not likely that any fire fighting equipment or
personnel or organization could have effected any significant reduction
in the amount of damage caused by the tremendous conflagration.
A study of numerous aerial photographs made prior to the atomic
bombings indicates that between 10 June and 9 August 1945 the Japanese
constructed fire breaks in certain areas of the cities in order to
control large scale fires. In general these fire breaks were not
effective because fires were started at so many locations
simultaneously. They appear, however, to have helped prevent fires
from spreading farther east into the main business and residential
section of Nagasaki.