"It's common today to state that the atomic bombing of Japan was obviously justified, on the grounds that the alternative would have been an invasion that had to be much worse. But at the time it was not so clear. The bulk of Japan's army was no threat to American forces: it was sequestered up in China, with American submarines keeping it from crossing to the home islands, and the great weight of Russia's army looming above, able to destroy it once a sufficient buildup had occurred. Japan's industry had largely been burned out. Early in 1945, U.S. strategic bombers had been assigned the task of destroying thirty to sixty large and small cities. By August, they had burned out fifty-eight of them.
Douglas MacArthur, who had run much of the Pacific campaign, didn't expect an invasion would be needed; Admiral Leahy, chairman of the Joint Chiefs of Staff, was later adamant that there had been no need for an atomic bomb; Curtis LeMay, the head of the strategic bombing force, agreed. Even Eisenhower, who'd had no qualms about killing thousands of opponents when it was necessary to safeguard his troops, was strongly hostile to it, as he explained at the time to Henry Stimson, the elderly secretary of war: 'I told him I was against it on two counts. First, the Japanese were ready to surrender and it wasn't necessary to hit them with that awful thing. Second, I hated to see our country be the first to use such a weapon. Well... the old gentleman got furious.'"
-- From David Bodanis book E = MC2: A Biography of the World's Most Famous Equation.