On Aug. 6, 1945, the United States dropped a uranium-fueled atomic bomb on Hiroshima, Japan. Three days later, another U.S. Army Air Forces B-29 repeated the attack on Nagasaki, Japan, with an even more powerful plutonium bomb.
Less than a month after the second bombing, Imperial Japan agreed to formally surrender on Sept. 2. That date marked the official end of World War II -- the bloodiest human or natural catastrophe in history, accounting for more than 65 million dead.
Each August, Americans in hindsight ponder the need for, the morality of, and the strategic rationale behind the dropping of the two bombs. Yet President Harry Truman's decision 73 years ago to use the novel, terrifying weapons was not considered particularly controversial, either right before or right after the attacks. Both cities were simply military targets.
Hiroshima was the headquarters of a Japanese army unit, and a key manufacturing center and port. Nagasaki -- a secondary target after clouds and smoke obscured the city of Kokura -- was the site of a huge Mitsubishi munitions plant.
Yet the sheer destructive power of the two bombs -- the 15-kiloton "Little Boy" Hiroshima bomb, and the 21-kiloton "Fat Man" Nagasaki bomb -- ensured catastrophic civilian casualties well beyond soldiers and munitions-plant workers. During the blasts, and long afterward due to radiation showers, perhaps 150,000 Japanese were killed.
Truman wanted to use the bombs to avoid invading the Japanese mainland. The recent battle for Okinawa resulted in an estimated 50,000 American casualties -- the bloodiest of all the American battles of the Pacific War. Truman's military planners warned that invasions of the Japanese mainland to end the war might cost the equivalent of 20 more Okinawa campaigns.
Japan's leaders swore that they would fight to the bitter end, bragging of their planned sacrifice as the "Glorious Death of One Hundred Million." They planned to draw on 10,000 suicide planes and 10 million soldiers, militiamen and irregulars.
Truman also had other worries.
The Soviet Union had done nothing during the war to harm Japan following its cynical 1941 non-aggression pact with the Japanese. But in August 1945, the Soviets were opportunistically preparing to invade a reeling Japanese empire in hopes of stripping Japan of its colonies in China, the Pacific and Korea. After Josef Stalin's recent Russian occupation of Eastern Europe, the idea of a Soviet Russia replacing Imperial Japan seemed not much better to Truman.
Thousands of Allied prisoners, as well as civilians in Japanese-occupied China, Southeast Asia and the Pacific, were dying each day the war dragged on. More than 1 million Japanese soldiers abroad were still brutally killing the innocent.
There were still other less publicized considerations. The incendiary B-29 bombing campaign from the distant Mariana Islands had already killed far more Japanese than would the two atomic bombs.
With new airfields on Okinawa, Gen. Curtis LeMay envisioned a far greater force of four-engine bombers to be sent on daily missions against Japan. LeMay would have had at his disposal nearly 10,000 four-engine bombers, including B-29s, along with transfers of idle B-24s, B-17s and British Lancaster bombers after the surrender of Germany three months earlier.
The ensuing napalm inferno might have precluded the invasion of Japan. But more nonstop firestorms also would have caused far more Japanese deaths than the two atomic bombs -- at a time when Japan was already blockaded by the U.S. Navy and running out of food and supplies.
In other words, the novelty of the two horrific atomic bombs helped to shock the Japanese emperor into a sudden surrender. And the abrupt end of the Pacific War saved millions of lives -- whether Asians under brutal Japanese occupation, Allied soldiers fighting against Japanese expeditionary armies, or Japanese civilians who likely would have been incinerated by an unimaginable second round of the firebombing campaign.
In the security and prosperity of peace, it is now common to fault Truman for his seemingly cruel decision. But in 1945, many Americans were blaming the U.S. government for thousands of American deaths from fighting in the Pacific. Right after the war, they complained that the atomic bombs should have been used even earlier to preclude nightmares such as Okinawa.
We also forget that Imperial Japan of 1945 was not the model democracy of Japan today, but a brutal, genocidal dictatorship. By August 1945, it already had butchered millions of Asians in occupied China, Southeast Asia and the Pacific.
Japan was still convinced that if the war could just continue, and it could kill thousands more American and British soldiers, then the exhausted Allies might finally negotiate a favorable armistice.
It is now hard to imagine any choices worse than dropping an atomic bomb. But in August 1945, there were some that most certainly were.