This week the North Korean dictator Kim Jong-un rattled his saber again, threatening the U.S. with a “thousand-fold” retaliation for the U.N. sanctions leveled against the already economically beleaguered country amounting to a billion dollars in lost export revenue. Although he didn’t mention nuclear weapons, everyone knows that the regime has been ramping up its nuclear capability for years, testing bombs underground and firing missiles eastward toward Japan and, ultimately, America. As this specter looms on our immediate horizon and the U.S. and our allies contemplate what to do with this potential threat to global security, on this, the 72nd anniversary of the only time in history that nuclear weapons have been used in conflict, let us reflect on the morality of that terrible week.

Seventy-two years ago the United States dropped atomic bombs on Hiroshima (Little Boy, August 6) and Nagasaki (Fat Man, August 9), leading to the announcement of the surrender of Imperial Japan (August 15) and the cessation of hostilities between our nations (September 2) and the termination of the Second World War.

Even before the atomic weapons were employed in the theater of war some of the scientists working on the Manhattan Project that built the bombs expressed their reservations once it was evident that the Germans had not completed their own nuclear program, and especially after they witnessed the awesome destructiveness of the Trinity test in New Mexico of the first ever atomic explosion on July 16. A year later, in 1946, the Federal Council of Churches issued a statement declaring, “As American Christians, we are deeply penitent for the irresponsible use already made of the atomic bomb. We are agreed that, whatever be one’s judgment of the war in principle, the surprise bombings of Hiroshima and Nagasaki are morally indefensible.”

Hiroshima after the bomb, with the signature of Paul Tibbets, pilot of the Enola Gay, which dropped the "Little Boy" weapon. Credit: U.S. Navy Wikimedia

In 1967 the MIT linguist and tireless American critic Noam Chomsky went even further, calling the bombings “the most unspeakable crimes in history.” In all of human history? That’s a serious charge. Many others have followed in this ethical vein. In his 2009 book Worse Than War, for example, the historian of genocide Daniel Goldhagen went so far as to accuse President Harry S. Truman of being “a mass murderer” for deciding “to snuff out the lives of approximately 300,000 men, women and children.” Equating mass murder with genocide and painting with a very broad brush, Goldhagen lumped Truman in with Hitler, Stalin, Mao Zedong, and Pol Pot as genocidal “eliminationists”.

This goes too far along the moralizing scale and should serve as a corrective to our evaluation of when it is ever just to use such weapons. Motive matters. In their genocidal actions against targeted people, Hitler, Stalin, Mao, and Pol Pot had as their objective the total elimination of a whole people. The killing would only stop when every last pursued person was exterminated. Truman’s motivation in dropping the bombs was to end the war, not to eliminate the Japanese people. If eliminationism was the goal, then the U.S. would never have implemented the Marshall Plan after the war to rebuild both Japan and Germany.

In point of fact, not only did Little Boy and Fat Man end the war and stop the killing, they very likely saved millions of lives, both Japanese and American. My father was quite possibly one of them. During the Second World War Richard Shermer was an electrician on the USS Wren, a Navy destroyer assigned to escort aircraft carriers and other large capital ships to protect them from Japanese submarines and Kamikaze planes and he was part of the larger fleet that was working its way toward Japan for a planned invasion of the islands. Although this personal connection is not a justificatory argument, my father told me that everyone on board dreaded the invasion option because they had heard of the horrific carnage resulting from the invasion of just two tiny islands held by the Japanese—Iwo Jima and Okinawa. What happened there foretold what would very likely result from a full-scale offensive on the Japanese mainland, but with orders of magnitude higher body counts.

Iwo Jima is a small volcanic rock 700 miles from Japan. In a battle that ground on for 36 days, over 19,000 Americans were wounded and another 6,821 were killed. That’s nothing compared to the Japanese carnage, in which only 216 soldiers survived the invasion from the total of 22,060 at the start, a 99.9 percent death rate. At only 340 miles from the Japanese mainland the conquest of Okinawa resulted in a staggering body count of 240,931 dead, including 14,009 American soldiers, 77,166 Japanese soldiers, plus an additional 149,193 Japanese civilians living on the island who either died fighting or committed suicide rather than let themselves be captured. Imagine, then, what the butchery would have been had the U.S. invaded the Japanese homeland that was bristling with 2.3 million ferocious fighters and 28 million determined civilian militia, all prepared to defend their nation to death.

We don’t need to imagine it. Truman’s advisors calculated that between 250,000 and 1,000,000 American lives would be lost in such an operation. This is a fraction of the estimated Japanese death toll, which General Douglas MacArthur put at a ratio of 22:1—22 dead Japanese for every one dead American—or 5.5 million dead Japanese. Compare these figures to the actual number who died as a result of the atomic bombs: 90,000–166,000 in Hiroshima and 60,000–80,000 for Nagasaki.

What would have happened had we not dropped the bombs? In such a counterfactual thought experiment, General Curtis LeMay and his fleet of B-29 bombers would have continued pummeling Japanese cities into rubble before the invasion. There is little doubt that the casualties, death, and property destruction from conventional bombs would have been just as high as that produced by the two atomic bombs, perhaps higher. Compare the TNT equivalency of Little Boy’s 16,000 tons with the U.S. Strategic Bombing Survey estimate that this was the equivalent of 220 B-29s carrying 1,200 tons of incendiary bombs, 400 tons of high-explosive bombs, and 500 tons of anti-personnel fragmentation bombs, with an equivalent number of casualties. Contrast this with what happened on the night of March 9-10, 1945, when 279 B-29s dropped 1,665 tons of bombs on Tokyo, leveling 15.8 square miles of the city, killing 88,000 people, injuring another 41,000, and leaving another one million homeless.

Such counterfactuals and moral thought experiments are designed to test our ethical intuitions, such as the famous trolley dilemma in which you are standing next to a fork in a railroad line with a switch to divert a trolley car that is about to kill five workers on the track. If you pull the switch and divert the trolley down a side track it will kill one worker instead. Would you throw the switch that would save five people but kill one person? Most people say that they would. In this sense, the use of atomic bombs to bring to an end the worst war in human history was the moral equivalent of pulling the trolley switch. Although we might be reticent to call the utter destruction of these two cities a moral act—and the nuclear option should always be last on the list of strategies, including dealing with North Korea—as moral dilemmas go it seems clear enough that dropping the atomic bombs was the necessary and right decision to make.

That does not mean that we should do the same with North Korea, of course. That’s a different moral calculation altogether.