In December, the Defense Science Board—an independent group of experts and former officials that provides advice to the Defense Department—submitted a report advising the Pentagon to invest in low-yield nuclear weapons that could provide “a rapid, tailored nuclear option for limited use.” This recommendation struck a familiar note. In 2003, the board issued a study entitled “Future Strategic Strike Forces” that suggested building small nuclear weapons with “great precision, deep penetration, [and] greatly reduced” yield and radioactivity. The board’s call led to investments in new warhead designs such as the Robust Nuclear Earth Penetrator—a warhead designed to destroy deeply buried or hardened targets including underground military command centers—and the Reliable Replacement Warhead. Both programs were cancelled in 2008, after millions of dollars had been spent.
Despite the board’s renewed interest in smaller nuclear weapons, and in weapons tailored for limited uses or specific effects, any effort to develop these weapons would encounter the same problem that earlier such efforts have encountered: It is impossible to determine if introducing weapons with these characteristics into the US stockpile, and planning for their use in certain scenarios, would strengthen deterrence or make nuclear war by miscalculation more likely. Building “mini” or tailored nuclear weapons might well lower the threshold to nuclear war; risking that outcome would only make sense if it were absolutely clear that introducing these weapons would remedy some dangerous weakness in deterrence.
Fortunately, no such weakness exists. Any nation using nuclear weapons against the United States or its allies risks a devastating response whose negative consequences would far outweigh any gains delivered by crossing the nuclear threshold. The United States has always possessed the means to employ a small number of nuclear weapons with relatively low yields—between, say, half a kiloton and 50 kilotons. In fact, the inventory of such weapons used to be massive; thousands of weapons with yields under 50 kilotons were deployed as artillery shells, land mines, short-range ballistic missiles, torpedoes, depth charges, anti-aircraft missiles, and even nuclear backpack weapons.
The current US tactical nuclear arsenal is comprised of approximately 500 B61 gravity bombs, which have three tactical versions—the B61-3, -4, and -10—with yields as low as .3 kilotons. The US Air Force deploys 150 to 200 B61s at six NATO air bases in five countries. Additional weapons are stored in the United States for possible overseas deployment. Also available is the W-80-1 warhead, deployed on hundreds of US air-launched cruise missiles, with a variable yield that can be set as low as 5 kilotons.
This list of “smaller” nuclear weapons demonstrates that there are no significant “gaps” in US nuclear capabilities that potential adversaries such as Russia, China, and North Korea could exploit.
That is why, today as in 2003, the Pentagon has no military requirement for the board’s cryptically-named “tailored nuclear option for limited use.” The military understands better than anyone the danger and unpredictability of using nuclear weapons. The military also understands how unlikely it is that any use of nuclear weapons against a nuclear-armed nation would remain “limited.” That is why the vast majority of so-called “tactical” nuclear weapons have been retired from service.
The theory that Russia or China might perceive some advantage in escalating to nuclear use during a conventional conflict is just that—a theory. Such notions are gleaned from worst-case analyses of rival nations’ military-strategic literature, force posture, and military exercises. All of this amounts to ambiguous data whose credibility is hardly beyond doubt. For example, Russian military commanders may simply find it unacceptable to admit in their writings that Russia would lose a prolonged conventional war against NATO. To save face (and their careers), these commanders might postulate that limited nuclear strikes against a small number of high-value NATO targets would cause the alliance to negotiate an end to hostilities—rather than retaliating in kind with “limited” nuclear strikes in Russia. Any such assumption by Russia is reckless and almost certainly incorrect. In NATO countries, there would be overwhelming political and emotional pressure to respond to Russia’s “limited” strikes with nuclear counterstrikes. Moreover, NATO’s declared intention is to respond to any nuclear attack with a devastating nuclear counterattack. The resulting destruction on both sides would be anything but “limited.” The Russians may delude themselves strategically, but the United States and its allies aren’t required to do the same.
The alliance did delude itself in the 1960s and 1970s, when it claimed that responding to a Soviet invasion of Western Europe with “limited nuclear options” could achieve acceptable outcomes. We now know from Soviet archives that Moscow had no intention of invading Western Europe—but if war had broken out and NATO had used battlefield nuclear weapons against Soviet tank armies, the Soviets would have launched a nuclear response, possibly including strikes on the US homeland. This dilemma was clear well before the end of the Cold War. That is why, beginning in 1977, NATO began to drastically reduce its inventory of “tactical” nuclear weapons to the minimum number necessary for deterrence.
In any event, the paradox of nuclear deterrence is that controlling the strategic calculus of one’s adversaries is necessary—but doing so reliably is impossible. Nuclear weapons are best maintained as weapons of last resort, not as weapons that might magically alter in one’s favor the terms of a conventional conflict. For Washington, this means that the highest strategic priority, in both Europe and Asia, is to deter conflict by maintaining conventional military forces that can defeat aggression against the territory of US allies and the vital interests of both allies and the United States itself. Such capabilities keep the nuclear threshold as high as possible. If the threshold is crossed nevertheless, the United States and its allies have and always have had credible limited nuclear options that could be employed anywhere on the globe.
Just as in the early 2000s, current proponents of mini-nukes or of vague “limited nuclear options” offer no convincing evidence that new weapons in this category are needed—or more importantly, that they would make nuclear use less likely. Instead, potential nuclear adversaries are likely to see the acquisition of additional weapons in this category as an indication that US opposition to nuclear use has decreased and that Washington may be the first to cross the nuclear threshold. Such an outcome would undermine global stability and increase the risk of nuclear war. Defense resources are better spent on strengthening US conventional forces.