Was the bombing of Hiroshima necessary?
Whether one considers the atomic bombing of Hiroshima necessary is dependent upon whether one agrees that U.S. policy towards Japan should have been one of demanding unconditional surrender of the Japanese. If one believes that that demand was justified, then the atomic bombing of Hiroshima was justified. The reason for this is that the most compelling argument for the use of the bomb code-named "Little Boy," a 15-kiloton (or, roughly 15,000 tons of TNT) weapon, was that its use would convince Japan's Emperor Hirohito and his military commanders of the futility of resisting the overwhelming power the United States could bring to bear against Japan. The alternative to using the atomic bombs was a full-scale invasion of the Japanese mainland, an operation that, it was calculated, would result in as many as one million American casualties. If the use of the bombs against Hiroshima and Nagasaki--and the debate over the use of "Fat Man" to destroy the latter city a few days after the Hiroshima bombing is far more intriguing than the debate over the Hiroshima bombing--would convince the emperor to surrender and accept the U.S. occupation that would entail, then the costs in Japanese lives would be far lower than would be the case if the U.S. did launch an invasion, and the United States would also be spared the enormous losses of life that would have resulted from an invasion. In other words, the use of the atomic bombs saved untold millions of lives, as an invasion would have been much bloodier and far more protracted.
Lost in much of the debate surrounding the justification for the Hiroshima bombing was the toll in lives and property destroyed in conventional and fire-bombings of cities, not all of which may have been militarily necessary, although second-guessing war-time commanders in the midst of the most horrific conflagration in human history is an exercise of dubious morality. For example, the firebombing of the German city of Dresden killed around 135,000 people, while the firebombing of Tokyo killed around 100,000 Japanese with hundreds of thousands of more people wounded. These bombings killed more people than the atomic bombings of Hiroshima and Nagasaki.
Again, though, the central question is whether the U.S. policy of unconditional surrender was justified. The answer to that question--and many Japanese agree--is yes, the policy was justified. Japanese militarism under the leadership of Hideki Tojo, an army general and prime minister of Japan during the war, was extremely well-entrenched in Japanese society. The fanaticism displayed by Japanese troops during the War in the Pacific had convinced American leaders of the necessity of totally destroying Japan's governing institutions. Only through the total defeat of Japan could Japanese society be demilitarized, and in this the late U.S. Army General Douglas MacArthur, who would govern post-war Japan, was absolutely correct. The United States was able to impose a liberal, democratic constitution upon the Japanese that banned offensive military capabilities such as those that had enabled that country's imperialist expansionism during the 1930s and early-1940s. Absent a policy of unconditional surrender, such an accomplishment, still felt today, would have been impossible.
In conclusion, then, the policy of unconditional surrender was correct, and the bombing of Hiroshima, then, was also correct.