Harry S. Truman claimed, for the rest of his life [after ordering that nuclear weapons be used in warfare], to have lost no sleep over his decision, but his behavior suggests otherwise. On the day the bomb was first tested in the New Mexico desert he wrote a note to himself speculating that "machines are ahead of morals by some centuries, and when morals catch up perhaps there'll be no reason for any of it." A year later he placed his concerns in a broader context: "[T]he human animal and his emotions change not much from age to age. He must change now or he faces absolute and complete destruction and maybe the insect age or an atmosphereless planet will succeed him." "It is a terrible thing," he told a group of advisers in 1948, "to order the use of something that ... is so terribly destructive, destructive beyond anything we have ever had.... So we have got to treat this differently from rifles and cannon and ordinary things like that."SOURCE: The Cold War: A New History, by John Lewis Gaddis (Penguin, 2005), pp. 53-55 (multiple reviews here)
The words were prosaic—Truman was a matter-of-fact man—but the implications were revolutionary. Political leaders had almost always in the past left it to their military chiefs to decide the weapons to be used in fighting wars, regardless of how much destruction they might cause. Clausewitz's warnings had done little over the years to alter this tendency. Lincoln gave his generals a free hand to do whatever it took to defeat the Confederacy: well over 600,000 Americans died before their Civil War came to an end. Civilians imposed few constraints on militaries in World War I, with devastating consequences: some 21,000 British troops died in a single day—most of them in a single hour—at the Battle of the Somme. Anglo-American strategic bombing produced civilian casualties running into the tens of thousands on many nights during World War II, without anyone awakening Churchill or Roosevelt each time this happened. And Truman himself had left it to the Army Air Force to determine when and where the first atomic weapons would be dropped: the names "Hiroshima" and "Nagasaki" were no more familiar to him, before the bombs fell, than they were to anyone else.
After that happened, though, Truman demanded a sharp break from past practice. He insisted that a civilian agency, not the military, control access to atomic bombs and their further development. He also proposed, in 1946, turning all such weapons and the means of producing them over to the newly established United Nations—although under the Baruch Plan (named for elder statesman Bernard Baruch, who presented it) the Americans would not relinquish their monopoly until a foolproof system of international inspections was in place. In the meantime, and despite repeated requests from his increasingly frustrated war planners, Truman refused to clarify the circumstances in which they could count on using atomic bombs in any future war. That decision would remain a presidential prerogative: he did not want "some dashing lieutenant colonel decid[ing] when would be the proper time to drop one."
There were elements of illogic in Truman's position. It made integrating nuclear weapons into existing armed forces impossible. It left unclear how the American atomic monopoly might be used to induce greater political cooperation from the Soviet Union. It impeded attempts to make deterrence work: the administration expected its new weapons to keep Stalin from exploiting the Red Army's manpower advantage in Europe, but with the Pentagon excluded from even basic information about the number and capabilities of these devices, it was not at all apparent how this was to happen. It is likely, indeed, that during the first few years of the postwar era, Soviet intelligence knew more about American atomic bombs than the United States Joint Chiefs of Staff did. Moscow's spies—having penetrated the top levels of the British intelligence establishment—were that good, while Truman's determination to maintain civilian supremacy over his own military establishment was that strong.
In the long run, these lapses proved less important than the precedent Truman set. For by denying the military control over atomic weapons, he reasserted civilian authority over how wars were to be fought. Without ever having read Clausewitz—at least as far as we know—the president revived that strategist's great principle that war must be the instrument of politics, rather than the other way around. Little in Truman's background would have predicted this outcome. His military experience was that of a World War I artillery captain. He had been a failed businessman, and a successful but unremarkable politician. He would never have reached the presidency had Roosevelt not plucked him from the Senate to be his vice-presidential running mate in 1944, and then died.
But Truman did have one unique qualification for demanding a return to Clausewitz: after August, 1945, he had the ability, by issuing a single order, to bring about more death and destruction than any other individual in history had ever been able to accomplish. That stark fact caused this ordinary man to do an extraordinary thing. He reversed a pattern in human behavior so ancient that its origins lay shrouded in the mists of time: that when weapons are developed, they will be used.