The nukes were a gratuitious showcase of nuclear weapons.
"The Japanese had, in fact, already sued for peace. The atomic bomb played no decisive part, from a purely military point of view, in the defeat of Japan." Fleet Admiral Chester W. Nimitz, Commander in Chief of the U.S. Pacific Fleet.[89]
"The use of [the atomic bombs] at Hiroshima and Nagasaki was of no material assistance in our war against Japan. The Japanese were already defeated and ready to surrender because of the effective sea blockade and the successful bombing with conventional weapons... The lethal possibilities of atomic warfare in the future are frightening. My own feeling was that in being the first to use it, we had adopted an ethical standard common to the barbarians of the Dark Ages. I was not taught to make war in that fashion, and wars cannot be won by destroying women and children." Fleet Admiral William D. Leahy, Chief of Staff to President Truman.[101]
"There is little point in attempting precisely to impute Japan's unconditional surrender to any one of the numerous causes which jointly and cumulatively were responsible for Japan's disaster. The time lapse between military impotence and political acceptance of the inevitable might have been shorter had the political structure of Japan permitted a more rapid and decisive determination of national policies. Nevertheless, it seems clear that, even without the atomic bombing attacks, air supremacy over Japan could have exerted sufficient pressure to bring about unconditional surrender and obviate the need for invasion.
Based on a detailed investigation of all the facts, and supported by the testimony of the surviving Japanese leaders involved, it is the Survey's opinion that certainly prior to 31 December 1945, and in all probability prior to 1 November 1945, Japan would have surrendered even if the atomic bombs had not been dropped, even if Russia had not entered the war, and even if no invasion had been planned or contemplated."[88][89]
In the documentary The Fog of War, former U.S. Secretary of Defense Robert S. McNamara recalls General Curtis LeMay, who relayed the Presidential order to drop nuclear bombs on Japan,[75] said:
"'If we'd lost the war, we'd all have been prosecuted as war criminals.' And I think he's right. He, and I'd say I, were behaving as war criminals. LeMay recognized that what he was doing would be thought immoral if his side had lost. But what makes it immoral if you lose and not immoral if you win?"[76][77]
http://en.m.wikipedia.org/wiki/Debate_over_the_atomic_bombings_of_Hiroshima_and_Nagasaki#section_2