If I recall, Nagasaki was added as a potential target for an atomic bomb after they removed Kyoto due to it's cultural significance to the Japanese people. That tends to lend support to the idea that they were not looking to create damage above and beyond what was strictly necessary to get Japan to surrender.
It's my understanding that Nagasaki was not the primary target, but switched to at the last minute due to conditions (weather?). They had a hierarchy of targets and some method by which to rank them, and I've not seen anywhere that that ranking was anything like "maximum population". Nagasaki was not an optimal terrain to kill civilians, it was picked because of its waterways which were somehow important for naval activity.
"The Target Committee appointed by President Harry Truman to decide which Japanese cities would receive the Little Boy and Fat Man atomic bombings did not place Nagasaki among their top two choices. Instead they identified Kokura as the second target after Hiroshima. In Kokura, a city of 130,000 people on the island of Kyushu, the Japanese operated one of their biggest ordnance factories, manufacturing among other things chemical weapons. The Americans knew all this, but strangely had not targeted the city yet in their conventional bombing campaign. That was one of the reasons the Target Committee thought it would be a good option after Hiroshima.
The third choice, Nagasaki was a port city located about 100 miles from Kokura. It was larger, with an approximate population of 263,000 people, and some major military facilities, including two Mitsubishi military factories. Nagasaki also was an important port city. Like Kokura and Hiroshima, it had not suffered much thus far from American conventional bombing."
"Over Kokura, clouds and smoke from nearby bombing raids obscured visibility. The Americans could see parts of the city, but they could not site directly on the city arsenal that was their target. Sweeney flew overhead until Japanese antiaircraft fire and fighters made things “a little hairy,” and it was obvious that sighting would be impossible. He then headed for his secondary target: Nagasaki. In Kokura, meanwhile, civilians who had taken shelter after the air raid signal heard the all-clear, emerged, and breathed sighs of relief. None of them knew then, of course, how close they had come to dying."
The bombing of the Japanese city of Nagasaki with the Fat Man plutonium bomb device on August 9, 1945, caused terrible human devastation and helped end World War II.
www.nationalww2museum.org
Looks like Nagasaki was switched to because the military target couldn't be identified positively.
www.newsweek.com
