While the United States used nuclear weapons against Japan in 1945, she did not use them against North Korea in 1950. With vanishingly few geopolitical—or even partisan political—guardrails to keep her from doing so, why did the United States not drop the bomb in the later war?

At 10:15 at night on September 6, 1950, a B-29 Superfortress of the 98th Bombardment Group of the US Far East Air Force dropped a Mark 4 plutonium bomb on Pyongyang, capital of North Korea. As with Hiroshima and Nagasaki, the effect of the air-burst explosion was devastating. A member of the US Postwar Bombing Survey, Captain Michael Thomas, cataloged the human toll: 29,000 dead due to blast and heat, another 35,000 from acute radiation syndrome (ARS), and thousands more of complications in the years and decades to come. But as was the case five years earlier, dropping the bomb had its intended strategic effect. In 1945, America’s “special weapon” had been used to bring the Pacific War to an end before the Soviet Union could strengthen its post-war position in the region. In 1950, a very similar weapon had been used to prevent Soviet- and Communist Chinese-backed North Korean forces from decisively defeating US and allied forces in Korea. In both cases, the humanitarian toll was staggering—as was anticipated. And in both cases, the strategic payoff made that toll seem acceptable, at least to those US decision-makers who had to make the hard strategic decisions.

This is the stuff of counterfactual history, of course. While the US did use nuclear weapons against Japan in 1945, it did not use them against North Korea in 1950.

But it very well might have.

By the end of the summer of 1950, things were looking bleak for the US and its allies. North Korean forces had routed those of the Republic of Korea, the US, and the United Nations, forcing them to retreat to a small pocket in the peninsula’s extreme southeastern corner. Despite support from the air and sea, there was a genuine prospect that the US-backed forces would be driven into the sea—with catastrophic results for the fledgling South Korean republic, the nascent UN collective security system, and America’s standing as leader of the anti-communist Free World. As far as many American decision-makers were concerned, if the use of atomic weapons were needed to forestall a defeat at the North Koreans’ hands, they should be used without hesitation.

Nor were the permissive conditions absent. By 1950, the US had nearly 300 Mark 4 bombs in its arsenal, a bomber capable of delivering these bombs, and a world-wide basing system that allowed these bombers to drop these bombs on almost every major city on the planet. On the other hand, the Soviets had only just conducted their first atomic test explosion in August 1949 and did not manage to weaponize the technology until 1951. The PRC was years away from its even first test explosion. Neither the USSR nor the PRC had the bases or bombers needed to threaten the United States directly. If the US had decided to US nuclear weapons against North Korea, it could do so knowing that no retaliatory strike was conceivable.

And, of course, there was precedent. The US had used these special weapons on two prior occasions and to satisfactory effect. This had short-circuited the emergence of whatever nuclear taboo some might have hoped would develop. Indeed, by early July 1950, the Pentagon and the commander-in-chief of the Pacific fleet presumed that, if South Korea’s situation became any more desperate, Congress and the public would actually demand the use of atomic weapons.

No. If the US had decided to use nuclear weapons against North Korea, there were vanishingly few geopolitical—or even partisan political—guardrails to keep it from doing so.

The real historical puzzle, then, is not why nuclear weapons were used against Japan in 1945. There was no convincing argument not to. The real puzzle is why they were not used against North Korea.

With the benefit of hindsight, of course, we know the answer to that question. The Pusan perimeter held just long enough for General MacArthur to carry out his now-famous amphibious assault at Inchon, about 20 miles west of Seoul. But hindsight is always 20-20. If we put ourselves behind the Resolute Desk in the Oval Office in late summer 1950, the certain success of MacArthur’s bold counter-strike was, well, not all that certain. It was deemed by many of the president’s most trusted advisors to be risky to the point of recklessness. Almost no one, other than MacArthur of course, had any faith that Operation Chromite would succeed—especially to the game-changing degree that it ultimately did. No, viewed from behind the Resolute Desk, through the fog of war, and facing the genuine prospect of a high-stakes defeat that might literally change the course of history, the rational thing to do was to use however many of the available Mark 3s as might be necessary to destroy the enemy’s will or ability to resist.

So why did Truman not use nuclear weapons against North Korea?

Of course, a decision on this scale is the vector sum of many different pressures and forces. Partisan political concerns, interservice rivalries, alliance diplomacy, miscommunication, personal chemistries, standard operating procedures—all of these factors were doubtless at play. But the most crucial factor, I would argue, the factor that ultimately rendered the prospects for nuclear war against North Korea vanishingly small, was the Cold War prism through which US leaders viewed the war on the peninsula. This was the great, eternal iron law that constrained US actions and even the thought processes that motivated and constrained these actions. The US did not view the war in Korea as significant in and of itself. Instead, it viewed the war on the peninsula as one flashpoint in the global existential struggle with the USSR and its vassal states like the newly minted PRC. The entire war and all its associated nuclear diplomacy were viewed through that prism. The question, then, was not, what will befall the RoK? Rather, it was, would the USSR intervene in Korea? Would the PRC take advantage of the distraction and invade Taiwan? And even, would this undermine the US’s special strategic relationship with its key ally the UK?

Viewed in this way—as an episode that could lead to world war or, short of that, weaken the Free World in its titanic struggle with communism—America’s special weapons came to be viewed by senior political leaders not as weapons of war, but as tools of diplomacy. In this sense, and counter to the logic that using these weapons would demonstrate American power and resolve, the belief prevailed that merely moving them around could be used to send those signals. And this growing allergy to actual use among the civilian leadership was reinforced by a developing consensus in the military that the general deterrent value of atomic weapons unused far exceeded the benefits that might flow from their employment with indeterminate results on a remote battlefield. Simply put, the military professionals’ understanding of the psychology of nuclear weapons was evolving in ways that made them increasingly reluctant to weaken deterrence through precipitate and potentially indecisive action against the North Koreans.

And that is why the US did not use nuclear weapons in the Autumn of 1950.

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The featured image is a picture of an atomic bomb explosion, from FEMA (U.S. Federal Emergency Management Agency) publicity poster. All FEMA images are in the public domain in the United States, and this image appears here courtesy of Wikimedia Commons.

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