THE SELECTION OF THE TARGET

THE SELECTION OF THE TARGET
Some of the most frequent queries concerning the atomic
bombs are those dealing with the selection of the targets
and the decision as to when the bombs would be used.
The approximate date for the first use of the bomb was
set in the fall of 1942 after the Army had taken over the
direction of and responsibility for the atomic bomb project.
At that time, under the scientific assumptions which turned
out to be correct, the summer of 1945 was named as the
most likely date when sufficient production would have
been achieved to make it possible actually to construct and
utilize an atomic bomb. It was essential before this time to
develop the technique of constructing and detonating the
bomb and to make an almost infinite number of scientific

and engineering developments and tests. Between the fall
of 1942 and June 1945, the estimated probabilities of success
had risen from about 60% to above 90%; however,
not until July 16, 1945, when the first full-scale test took
place in New Mexico, was it conclusively proven that the
theories, calculations, and engineering were correct and
that the bomb would be successful.
The test in New Mexico was held 6 days after sufficient
material had become available for the first bomb. The
Hiroshima bomb was ready awaiting suitable weather on
July 31st, and the Nagasaki bomb was used as soon after
the Hiroshima bomb as it was practicable to operate the
second mission.
The work on the actual selection of targets for the atomic
bomb was begun in the spring of 1945. This was done in
close cooperation with the Commanding General, Army
Air Forces, and his Headquarters. A number of experts in
various fields assisted in the study. These included mathematicians,
theoretical physicists, experts on the blast effects
of bombs, weather consultants, and various other
specialists. Some of the important considerations were:
A. The range of the aircraft which would carry the bomb.
B. The desirability of visual bombing in order to insure the
most effective use of the bomb.
C. Probable weather conditions in the target areas.
D. Importance of having one primary and two secondary
targets for each mission, so that if weather conditions prohibited
bombing the target there would be at least two alternates.
E. Selection of targets to produce the greatest military effect
on the Japanese people and thereby most effectively
shorten the war.
F. The morale effect upon the enemy.
These led in turn to the following:
A. Since the atomic bomb was expected to produce its
greatest amount of damage by primary blast effect, and
next greatest by fires, the targets should contain a large
percentage of closely-built frame buildings and other construction
that would be most susceptible to damage by blast
and fire.
B. The maximum blast effect of the bomb was calculated
to extend over an area of approximately 1 mile in radius;
therefore the selected targets should contain a densely builtup
area of at least this size.

C. The selected targets should have a high military strategic
value.
D. The first target should be relatively untouched by previous
bombing, in order that the effect of a single atomic
bomb could be determined.
The weather records showed that for five years there
had never been two successive good visual bombing days
over Tokyo, indicating what might be expected over other
targets in the home islands. The worst month of the year
for visual bombing was believed to be June, after which
the weather should improve slightly during July and August
and then become worse again during September. Since
good bombing conditions would occur rarely, the most intense
plans and preparations were necessary in order to
secure accurate weather forecasts and to arrange for full
utilization of whatever good weather might occur. It was
also very desirable to start the raids before September.