American bombers participated in Operation Gomorrah and the subsequent RAF attack on Dresden, where perhaps twenty thousand civilians died. But the United States Army Air Forces (USAAF) opposed the British policy of targeting residential areas, known as “de-housing.” Instead of the RAF’s nighttime “area” bombing, the strategic doctrine of the USAAF called for daytime “precision” bombing. Relying on the Norden bombsight — a device that combined a telescope, a mechanical computer, and an autopilot — the USAAF tried to destroy German factories, ports, military bases, and lines of communication. Precision bombing was rarely precise, and the vast majority of bombs still missed their targets. Nevertheless, American aircrews risked their lives conducting raids in broad daylight to avoid killing German civilians.
In the Pacific War a different set of rules applied. The Japanese were considered racially inferior, often depicted as monkeys or vermin in American propaganda. The Japanese had attacked the United States without warning. They had treated Allied prisoners of war with brutality, employed slave labor, and launched suicide attacks instead of surrendering. They had forced as many as two hundred thousand Korean women to serve as prostitutes in military brothels. They had killed almost one million Chinese civilians with chemical and biological weapons. They had killed millions of other civilians in China, Burma, Korea, Singapore, Malaysia, Cambodia, Vietnam, and the Philippines, war crimes driven by the Japanese belief in their own racial superiority.
At first, the United States conducted only precision bombing raids on Japan. But heavy cloud cover and high-altitude winds made it difficult to hit industrial targets. On the night of March 9, 1945, the Army Air Forces tried a new approach. American planes struck Tokyo with two thousand tons of bombs containing napalm and jellied gasoline. Although a major industrial area was destroyed, the real targets were block after block of Japanese buildings made of wood, paper, and bamboo. Within hours the firestorm consumed one quarter of the city. It killed about one hundred thousand civilians, and left about a million homeless. This was truly, in the words of historian John W. Dower, “war without mercy.”
The firebombing of Tokyo wasn’t condemned by President Roosevelt. On the contrary, it was soon followed by the firebombing of Nagoya, Osaka, Kobe, Kawasaki, and Yokohama. By the middle of June, the United States had laid waste to Japan’s six leading industrial cities. Then American planes launched incendiary attacks on dozens of smaller cities. The level of destruction varied considerably. About one quarter of Osaka was destroyed by fire, one third of Kawasaki, more than half of Kobe. Toyama, a city on the Sea of Japan with chemical plants and a population of about 125,000, was hit the hardest. After a nighttime raid by B-29 bombers, the proportion of Toyama still standing was an estimated 0.5 percent.
As Japanese cities vanished in flames, Leó Szilárd began to have doubts about the atomic bomb. He had been the first to push hard for its development in the United States, but he now opposed its use against Japanese civilians. In June 1945, Szilárd and a group of scientists at the University of Chicago sent a report to the leadership of the Manhattan Project, asking that the power of nuclear weapons be demonstrated to the world at “an appropriately selected uninhabited area.” A nuclear attack upon Japan, they contended, would harm the reputation of the United States, make it difficult to secure international control of “this new means of indiscriminate destruction,” and start a dangerous arms race. But the die had been cast. A committee of presidential advisers had already decided that a public demonstration of an atomic bomb was too risky, because the weapon might not work; that Japan should not be given any warning of a nuclear attack, for much the same reason; that the bomb should be aimed at a war plant surrounded by workers’ housing; and that the goal of the bombing would be “to make a profound psychological impression” on as many workers as possible.