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.