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