Many different explanations have been
offered as to why the atomic bomb was dropped on
Hiroshima. The Hiroshima
Peace Memorial Museum presents the following
explanation:
In the US, with
the atomic bomb development still
underway, it was decided in September
1944 to use the bomb against Japan. The
United States wanted to force Japan's
surrender as quickly as possible to
minimize American casualties. In
addition, the United States needed to use
the atomic bomb against Japan before the
Soviet Union entered the war to establish
US dominance after the war. Further, the
Americans wanted to use the world's first
atomic bomb for an actual attack and
observe its effect. For these reasons,
those in charge were in a hurry. Shortly
after successfully testing history's
first atomic explosion on July 16, 1945, the order to drop the atomic
bomb was issued on July 25.
Based on this order, a field
operation order dated August 2 called for
the attack to take place on August 6,
with Hiroshima to be the primary target.
It is thought that Hiroshima was selected
for the following reasons:
The size
and topography of the city made
it suitable for testing the
destructive capabilities of the
atomic bomb, and for confirming
the destructive effects later.
There
was a concentration of military
troops, installations, and
factories in Hiroshima that had
been spared previous bombing.
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The order to drop the first atomic bomb
named the cities of Hiroshima, Kokura, Niigata,
and Nagasaki as targets, and specified that
"Additional bombs will be delivered on the
above targets as soon as made ready by the
project staff. Further instructions will be
issued concerning targets other than those listed
above" (Instruction to General Carl Spaatz,
Commanding General, United States Army Strategic
Air Forces from General Thos. T. Handy, Acting
Chief of Staff.)
The
Hiroshima
Peace Memorial Museum website narrates that:
... it is
believed that the atomic bomb exploded
approximately 580 meters in the air over
the Shima Hospital in Saiku-machi (now
Otemachi 1 chome), about 300 meters
southeast of the Aioi Bridge. At the
instant of detonation, the temperature of
the air at the point of explosion
exceeded a million degrees Celsius (the
maximum temperature of conventional bombs
is approximately 5,000 °C). A white-hot
fireball appeared millionths of a second
after detonation. After 1 second, the
fireball reached a diameter of
approximately 280 meters. For the
following three seconds, it emitted
powerful heat rays, and continued to
shine visibly for approximately 10
seconds.
At the instant of explosion,
intense heat rays and radiation were
released in all directions. The pressure
on the surrounding air created a blast of
unimaginable force. The cloud generated
by the explosion rose on powerful
updrafts. As the pillar of radiation-laden
soot and smoke reached the bottom of the
stratosphere, it spread horizontally to a
diameter of several kilometers, forming a
giant mushroom cap. Of the energy
released, about 35% was in the form of
heat, 50% was blast, and about 15% was
radiation...
Because the A-bomb exploded
close to the center of the city, and
because 85% of the buildings were within
3 km of the hypocenter, destruction to
the city was nearly complete, with 90% of
buildings collapsed or burned. (August
1946 Survey by the Hiroshima City
Government)
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Approximately 140,000 people out of
Hiroshima's estimated population of 350,000 had
died by the end of December 1945.
The
Nagasaki
Atomic Bomb Museum explains that:
An atomic bomb
exploded over Nagasaki on August 9, 1945,
three days after the explosion of the
first atomic bomb over Hiroshima. The
bomb was assembled at Tinian Island on
August 6. On August 8, Field Order No.17
issued from the 20th Air Force
Headquarters on Guam called for its use
the following day on either Kokura, the
primary target, or Nagasaki, the
secondary target. That same day, the
Soviet Union declared war on Japan. The B-29
bomber "Bockscar" reached the
sky over Kokura on the morning of August
9 but abandoned the primary target
because of smoke cover and changed course
for Nagasaki, the secondary target, where
it dropped the atomic bomb at 11:02 a.m.
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