The biggest immediate impact of a Japanese nuclear weapon would have been raw panic in Beijing. Nuclear weapons gave China a deterrent against three powers: the United States, the USSR and Japan. As it happened, Japan’s conventional weakness and pacifist political approach made the latter unnecessary. However, the development of Japanese nukes would have forced China to worry greatly about the political independence of Tokyo from Washington. As long as Japan relied on the United States for its nuclear deterrent, Washington held the reins; Japanese nukes might open the door for a return to the pursuit of regional military hegemony. This, consequently, might have driven the Chinese back into the arms of the Russians, or at least accelerated the development of their own nuclear deterrent force.

During the Cold War, the United States supported selective nuclear proliferation as a means of deterring a Soviet invasion of Europe. The Russians might not believe that the United States would trade Berlin for New York, but they might find a British or French threat more credible.

Washington did not pursue the same strategy in Asia. Although Japan could easily match Britain or France in economic power and technological sophistication, the United States didn’t see fit to support Japanese nuclearization. Instead, the United States quashed Japanese nuclear ambitions whenever they appeared.

This decision was well considered, given the effect that Japanese nukes might have had on the course of global nuclear proliferation. But had the balance of power in East Asia shifted in a different direction, arming Japan with nukes might have made more sense. Such a development would have had huge implications for the spread of nuclear weapons across the world.

The Legacy of World War II: 

Japan briefly pursued atomic weapons during World War II, although its efforts came nowhere near matching those of Germany, much less the United States. However, the United States destroyed the project’s infrastructure early in the occupation, making clear that Japan would not soon rejoin the community of nations, at least in terms of self-defense. The precedent of Pearl Harbor rested heavily on American minds, and the idea that Japan might acquire weapons that would enable it to undertake a far more devastating sneak attack was deeply unpopular. While the United States supported British and tolerated French nuclear efforts, Japan was different; Britain and France were part of the victorious Allied coalition in World War II, while Japan was a defeated aggressor state.

As the only victim of a nuclear attack, Japan’s domestic politics made a nuclear turn difficult. However, during the 1960s, the Japanese government actively considered the development of a nuclear weapons program. Japanese Prime Minister Eisaku Sato argued that Japan needed nuclear weapons to match those of China; however, the United States demurred. Instead, the Johnson administration pressed for Japanese accession to the Nuclear Non-Proliferation Treaty, ending, for then, Japan’s nuclear ambitions.

Nuclear Decisions in Washington and Tokyo: 

What could have changed Washington’s mind, and consequently Tokyo’s calculations? The Sino-Soviet split undoubtedly played a role in U.S. wariness. A Japanese nuclear weapon might have quickly driven China back into the arms of the USSR, solidifying the Communist front in East Asia. But if the two socialist giants had not fallen out with one another, a Japanese nuclear deterrent might have looked much more appealing.

Japan’s constitution prohibits the acquisition of offensive weapons, leading to an endless series of linguistic obfuscation about the defensive nature of particular systems. Aircraft carriers, for example, become “helicopter destroyers.” There is little question that Japanese and American legal authorities would have found ways around the constitutional prohibition. Indeed, nuclear weapons intended primarily for deterrent purpose (rather tactical or strategic) arguably have an intrinsic “defensive” nature. And given the advanced nature of Japan’s economy, the Japanese Self-Defense Forces could have deployed nuclear weapons very soon after any decision to begin development.

In terms of delivery systems, Japan would likely have developed (or purchased from the United States) intermediate-range ballistic missiles, capable of striking the Asian mainland but not the United States. Eventually, the United States could have shared Polaris and Trident SLBM technology; nuclear submarine propulsion would have proven no obstacle after the development of nukes themselves. Long-range bombers might have been a stretch, but tactical aircraft (such as the F-4, and eventually the F-15) would have taken on a tactical nuclear role.

Impact: 

The biggest immediate impact of a Japanese nuclear weapon would have been raw panic in Beijing. Nuclear weapons gave China a deterrent against three powers: the United States, the USSR and Japan. As it happened, Japan’s conventional weakness and pacifist political approach made the latter unnecessary. However, the development of Japanese nukes would have forced China to worry greatly about the political independence of Tokyo from Washington. As long as Japan relied on the United States for its nuclear deterrent, Washington held the reins; Japanese nukes might open the door for a return to the pursuit of regional military hegemony. This, consequently, might have driven the Chinese back into the arms of the Russians, or at least accelerated the development of their own nuclear deterrent force.

Japanese nukes would have created similar alarm across the region. While Seoul, deeply dependent on the United States for security guarantees, would likely have adopted a “grin and bear it” attitude in the short run, it likely would have pursued its own program over the long term. Similarly, Japanese proliferation would have made it far more difficult for the United States to restrain Taiwan’s nuclear ambitions. Not wanting to be left behind, India would have pursued its own program with greater vigor and less political reticence.

More broadly, a nuclear Japan could not have managed the key role that Tokyo played in the development of the global nonproliferation regime. As history’s only victim of a nuclear attack, Japan’s diplomacy and money carried heavy weight in worldwide antinuclear efforts. These efforts would have suffered with a lack of Japanese participation, possibly with dire effects for the spread of nuclear weapons around the world.

In the long view, the decision on Washington’s part to curtail Japanese nuclear ambitions played out well. China moved farther and farther from Russia, Japan remained dependent on the United States, and both the regional and global nonproliferation regimes made critically important achievements. However, had the United States misread Sino-Soviet relations, or had certain segments of the Japanese government pressed harder, a much different reality might have ensued—one in which not just Japan, but many states across the region and the world, held nuclear weapons.

Robert Farley, a frequent contributor to the National Interest, is author of The Battleship Book. He serves as a Senior Lecturer at the Patterson School of Diplomacy and International Commerce at the University of Kentucky. His work includes military doctrine, national security, and maritime affairs. He blogs at Lawyers, Guns and Money and Information Dissemination and the Diplomat.

This was published last year and is being reposted due to reader interest.