Hiroshima was already on the list when the Targetting Committee requested details on the construction of Japanese building at the proposed bombing locations (Nagasaki was not on the list at this point). At the next meeting of the Targetting Committee, there was no discussion of preferred sites except that to note that “efficient targets” had already been destroyed and that a blast wave of 3 PSI was probably sufficient to destroy most buildings.

They had a handful of reinforced concrete buildings, but nothing in comparison to the last 70 years of construction

The center of the city [Hiroshima] 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.

In contrast to many modern aspects of Nagasaki, the residences almost without exception were of flimsy, typical Japanese construction, consisting of wood or wood-frame buildings, with wood walls with or without plaster, and tile roofs. Many of the smaller industries and business establishments were also housed in wooden buildings or flimsily built masonry buildings. Nagasaki had been permitted to grow for many years without conforming to any definite city zoning plan and therefore residences were constructed adjacent to factory buildings and to each other almost as close as it was possible to build them throughout the entire industrial valley.

The tallest building in the entity of Japan until the 60s was only about 60 metres tall.