What happened in that interval? The United States dropped a new weapon, the atomic bomb, on Hiroshima and then Nagasaki. Days later, the Pacific War was over, and America was victorious.
Tuesday, President Barack Obama announced he would visit Hiroshima, which no sitting president has done. His decision is bound to reopen the debate over President Harry Truman's use of nuclear weapons, the first and last time they were ever detonated in war.
That Navy ensign was my father, T.J. Chapman, who outlived the war and everything since, celebrating his 90th birthday last year. Had the bomb not been built and used, his life might have ended then, and I would never have been born. So I may be biased. But it has occurred to me that there could have been Japanese just my age who, because of those cataclysmic explosions, were never born.
The case that Truman erred is familiar. Critics say Japan would have surrendered soon anyway, that the entry of the Soviet Union into the war was the real reason for its capitulation, and that Truman was acting as much to block Josef Stalin from a postwar role in East Asia.
In "Bombing to Win: Air Power and Coercion in War," University of Chicago scholar Robert Pape concluded that the U.S. sea blockade and the Soviet invasion of Manchuria had convinced Japan's military leaders that the war was hopeless. The new weapon, in his view, didn't even hasten the day of surrender.
Other experts differ. The bombs "convinced the Japanese military that its strategy for defending the home islands was doomed," George Washington University political scientist Alexander Downes, author of "Targeting Civilians in War," told me. "Hiroshima and Nagasaki meant that the United States could simply sit offshore and vaporize the defenders rather than having to invade."
What is clear is that no president would have declined to use these weapons. After four years of unimaginably savage and costly fighting in the Pacific, any military option that offered hope of finally achieving victory had to be seized.
It wasn't certain that atomic bombs would work, but it was more than plausible. The potential benefit was enormous. Each day the war continued meant hundreds more Americans killed: Three U.S. Navy ships were lost just between the bombing of Nagasaki and the surrender.
Nor was there any special moral issue in using the new weapon. For years, Allied bombers had been slaughtering enemy civilians on a mass scale in Germany and Japan. More people died in the March firebombing of Tokyo than in Hiroshima.
An invasion of the island nation would have been apocalyptic. Estimates of the Japanese civilian casualties ranged into the millions, and the U.S. military anticipated as many as 1 million Americans would be killed or wounded.
In the effort to win the war, there were no humane formulas or foolproof answers. In electing to drop the bomb, Truman acted in good faith to advance an impeccable and humane purpose - successfully ending a catastrophic conflict that had been forced on us. There is no good reason for a U.S. apology.
That doesn't mean Obama is mistaken to visit Hiroshima. The need to use nuclear weapons there is debatable, but the urgency of preventing another use is not.
His call for a nuclear-free world is less important in that effort than his effort to make sure our nuclear arsenal is safe and reliable, to deter other nuclear powers. The Iran deal is another step in the right direction.
Having a wise, restrained leader in the Oval Office is also critically important. Donald Trump, who raised the possibility of nuclear retaliation against the Islamic State, doesn't qualify. The prospect of his finger on the trigger should give us -- and the rest of humanity -- nightmares.
Obama's visit to Hiroshima should not cause Americans to feel deep guilt about how our government used nuclear weapons in the past. But it should stimulate intense anxiety about how they might be used in the future.