The city of Hiroshima is located on the broad, flat delta of the Ota
River, which has 7 channel outlets dividing the city into six islands
which project into Hiroshima Bay. The city is almost entirely flat and
only slightly above sea level; to the northwest and northeast of the
city some hills rise to 700 feet. A single hill in the eastern part of
the city proper about 1/2 mile long and 221 feet in height interrupted
to some extent the spreading of the blast damage; otherwise the city
was fully exposed to the bomb. Of a city area of over 26 square miles,
only 7 square miles were completely built-up. There was no marked
separation of commercial, industrial, and residential zones. 75% of
the population was concentrated in the densely built-up area in the
center of the city.
Hiroshima was a city of considerable military importance. It contained
the 2nd Army Headquarters, which commanded the defense of all of
southern Japan. The city was a communications center, a storage point,
and an assembly area for troops. To quote a Japanese report, "Probably
more than a thousand times since the beginning of the war did the
Hiroshima citizens see off with cries of 'Banzai' the troops leaving
from the harbor."
The center of the city contained a number of reinforced concrete
buildings as well as lighter structures. Outside the center, the area
was congested by a dense collection of small wooden workshops set among
Japanese houses; a few larger industrial plants lay near the outskirts
of the city. The houses were of wooden construction with tile roofs.
Many of the industrial buildings also were of wood frame construction.
The city as a whole was highly susceptible to fire damage.
Some of the reinforced concrete buildings were of a far stronger
construction than is required by normal standards in America, because
of the earthquake danger in Japan. This exceptionally strong
construction undoubtedly accounted for the fact that the framework of
some of the buildings which were fairly close to the center of damage
in the city did not collapse.
The population of Hiroshima had reached a peak of over 380,000 earlier
in the war but prior to the atomic bombing the population had steadily
decreased because of a systematic evacuation ordered by the Japanese
government. At the time of the attack the population was approximately
255,000. This figure is based on the registered population, used by
the Japanese in computing ration quantities, and the estimates of
additional workers and troops who were brought into the city may not be
highly accurate. Hiroshima thus had approximately the same number of
people as the city of Providence, R.I., or Dallas, Tex.