Potential US responses to the Russian use of non-strategic nuclear weapons in Ukraine

When the rhetoric from the Russian political and military leadership turns to the possibility of a war pitting the United States and its NATO allies against Russia, the mention of nuclear weapons is usually close behind. Russian Foreign Minister Sergei Lavrov recently raised the nuclear specter over the Ukraine war, insisting that NATO is engaging in a proxy war with Russia. While insisting that Russia seeks to avoid nuclear war at all costs, he warned that the “danger is serious, real, and we must not underestimate it.”

This is double talk typical of Lavrov; through it, he attempts to paint Russia as a responsible actor, even though Russia is the only actor in this war that would consider using nuclear weapons. The Russian leadership has also used nuclear threats to signal its displeasure with the expansion of NATO, suggesting it will deploy nuclear-capable missiles near Finland and Sweden if they join the alliance.

Many of these nuclear threats are signals, meant to politically coerce. But what if Russian President Vladimir Putin decided to use a nuclear weapon in Ukraine to change the apparent negative direction of the Russian invasion there? Four response options seem at least plausible: the West could use a nuclear weapon or weapons against Russian forces, in or outside Ukraine; it could conduct a conventional military attack on Russian forces, in or outside Ukraine; it could continue its current policy of supplying Ukraine with weapons while avoiding direct conflict with the Russian military; or it could press Ukraine to settle the conflict, on terms that give Russia a face-saving out.

Responding in-kind to a Russian nuclear attack and caving to nuclear coercion are clearly unwise, but the other options have risks and uncertainties that make one thing obvious: Russian use of a nuclear weapon or weapons in Ukraine would greatly increase the likelihood of direct NATO-Russia conflict.

Russian nuclear doctrine and the war in Ukraine. So far, the Russian leadership pronouncements about potential nuclear weapons use seem to correspond to well-known Russian nuclear declaratory policy. This policy allows for the use of nuclear weapons should Russia detect ballistic missiles inbound to Russia or its allies, in response to the use of nuclear weapons or weapons of mass destruction against Russia or attacks against Russian nuclear command and control, and to halt aggression through conventional means that could threaten the “very existence of the state.” Of course, declaratory policy does not, in and of itself, necessarily limit the Russian leadership from using nuclear weapons in other circumstances. Other triggers could include a certain level of economic destruction, the loss of military capability, and the inability to sustain military operations—all of which possibly fall under threats to the very existence of the state, especially if that existence is defined as regime survival.

But one can argue that Russian declaratory policy is really meant to describe conditions for the use of strategic nuclear weapons. If Russia did use nuclear weapons in Ukraine, they would almost certainly be non-strategic nuclear weapons. There are multiple ways to define and understand what constitutes a non-strategic weapon, but the label is often a general reference to shorter-range, lower-yield nuclear weapons—sometimes referred to as tactical nuclear weapons—intended to be employed against theater targets. Russia’s threshold for the use of non-strategic nuclear weapons may be below that of its escalatory policy, given its deep reserve of thousands of non-strategic nuclear weapons and the dual conventional-nuclear capabilities of all its production-line missiles. These realities and Russian military writings suggest a war-fighting role for non-strategic nuclear weapons.

Russian use of non-strategic nuclear weapons in Ukraine could take several forms. They could be used for demonstration purposes—not targeting anything and not creating casualties—to coerce Ukraine and/or the West to agree to a settlement acceptable to Putin. Tactical nukes could be used to target military units to change the operational situation on the ground, although to do so significantly would likely require multiple non-strategic nuclear weapons strikes. Given the level of Russian barbarity and willingness to decimate urban areas, it is also conceivable that they could be used against a city as a form of ultimate coercion.

Regardless of reason, let us assume Russia has used a nuclear weapon in Ukraine. How do the West and the United States in particular react? The emotional noise following the use of a nuclear weapon in Ukraine would be deafening, both in terms of calls for restraint and of demands for retaliation. In many ways, the policy community is divided between those wanting an aggressive approach to the war that seeks to force a strategic defeat on Russia and those who want a more constrained approach to avoid a possible escalation of the conflict and the nuclear implications that go with it. Despite this divide, we can attempt to broadly break down the potential policy areas that cover the gamut of positions open to the United States and NATO, their implications, and their possible consequences.

Responding in kind. In any escalatory move, the first impulse may be to respond in kind. If your adversary moves along the escalation spectrum a notch, then perhaps you should as well, lest you lose the fight for escalation dominance.

The United States and NATO could respond in kind to a Russian use of a non-strategic nuclear weapon or weapons, perhaps via dual-capable aircraft, i.e. those that can carry conventional and nuclear weapons. In such a response, perhaps the most difficult problem involves choosing the target. That choice, of course, will be partly contingent on just what Russia has done.

In the scenario we are exploring, Russia has used a non-strategic nuclear weapon in Ukraine. To truly be “in-kind” in this scenario, the US and NATO would need to strike Russian targets in Ukraine—or otherwise significantly change the nature of the conflict by striking a target in Russia. There may be Russian military targets in Ukraine for which a low-yield nuclear strike would produce limited casualties. But to have a significant military impact, NATO would likely have to use multiple strikes. However,the potential for lasting impacts and the optic of two nuclear powers carrying out nuclear exchanges on the territory of a non-nuclear state would be politically infeasible. So, it’s probably safe to exclude a Western response in kind, in Ukraine, using tactical nuclear weapons.

Striking a target in Russia with a nuclear weapon, regardless of yield, fundamentally changes the conflict. In this scenario, Russia has not used a nuclear weapon against the United States, NATO, or any country with which the United States has extended nuclear deterrence guarantees. Using a nuclear weapon against Russia immediately turns the conflict into a Russia versus the United States and NATO war that has skipped all the conventional options for escalation management. Given the potential global consequences of a nuclear war between Russia and the United States and NATO, striking targets inside Russia with nuclear weapons is unlikely to be viewed by the US president as a viable option. So the option of a Western response in kind to a Russian use of non-strategic nuclear weapons in Ukraine can probably be set aside, given the targeting and extreme escalation ramifications of a Western use of nuclear weapons in Ukraine or in Russia.

And there is an additional, not insignificant reason to avoid a response in kind: Reinforcement of the norm against using nuclear weapons. By refusing to use nuclear weapons in response to a Russian nuclear attack in Ukraine, the United States and its NATO allies would draw a stark contrast between those who are and are not willing to use nuclear weapons, especially against non-nuclear states.

Conventional response and escalation. Despite the dangers of escalating the Ukraine conflict to a war between NATO and Russia, policy makers have non-nuclear options to respond to Russian use of one or more non-strategic nuclear weapons.

There are several employment options to consider. The first would be conventional strikes against Russian military targets in Ukraine. These could go after Russian units themselves, logistic hubs, or any number of platforms Russia is using to persecute the war. If the Russian use of nuclear weapons targeted Ukraine’s ability to fight, one targeting criteria to consider would be those targets that negate any Russian advantage gained by its use of nuclear weapons. A second option would be to target the platform used by Russia to carry out the strike—a platform that would almost certainly be based inside Russia itself.

It is fair to say that either of these options leads to an expansion of the conflict to one between Russia and the United States and its NATO allies. The fundamental change here is the deliberate targeting of the Russian military by US and NATO platforms. While Ukraine is using US and NATO weapons to kill Russian troops, there is an escalation salient between this and NATO and US forces directly attacking the Russian military. The argument can certainly be made that crossing the conventional-nuclear threshold by Russia against Ukraine warrants the entry of NATO and the United States into the conflict. This would reinforce the view that the use of nuclear weapons in such scenarios, and especially for coercive reasons, is unacceptable. Of course, this would lead to a Russian response against NATO. Despite most of its ground forces being caught in the war in Ukraine, Russia could attempt to strike US and NATO infrastructure both in Europe and the United States, the latter being through land-strike missions from submarines in the Atlantic.

A conventional response against Russian use of nuclear weapons in Ukraine carries with it clear escalatory risks, although lower than those associated with a symmetrical response. However, the impetus for some response would be intense and arguably justified. A conventional response is a viable policy option that seeks to maintain some control over escalation while acknowledging the need to respond.

Staying the Course. In a third type of response, the United States and NATO could stay the course and continue to provide military aid to the Ukrainians without escalating the war with attacks against Russia or Russian military forces. The core of this response is the realization that the current trajectory in the Russia-Ukraine conflict favors Ukraine and that Russia’s use of nuclear weapons is an act of desperation. Russia is losing and the use of nuclear weapons in Ukraine, whether to stop Ukraine’s military or to coerce Ukraine and the West, seems to be the next only available option for Putin. This policy option attempts to keep the conflict as much confined to Ukraine-Russia as possible while also weakening Russia by continuing to support and enable Ukrainian successes.

A concern in this scenario would be the potential fate of Ukrainian resistance given casualties it would sustain from nuclear strikes.  The United States and NATO could face the possibility that the current level of aid would be insufficient to maintain the Ukrainian Army as a viable fighting force after it has sustained casualties from nuclear strikes. Another concern would be the takeaway Russia and other countries would take from a lack of symmetrical response—namely that nuclear employment works and carries with it less costs than originally thought.

There are two distinct pathways, among others, that stand out and follow from this scenario. We will call the first “Putin’s Corner.” If the US, NATO, and Ukraine can keep Ukraine in the fight after the use of non-strategic nuclear weapons, and the Russian military trajectory continues to be negative, Putin may feel his options are limited even further. Given the commonly held analytic line that Putin believes he cannot afford to lose in Ukraine, one of his last options would be to escalate the Ukraine war into a war with NATO.

At first glance, a decision by Russia to escalate to a Russia-NATO war seems reckless given the current weakened state of Russia’s forces, especially its ground forces. To be clear, the intent would not be to invade a NATO country or carry out an extended war with NATO. Putin’s intent in escalating the war would be to call the bluff of the United States and NATO. Rightfully believing that NATO does not want a war with Russia, Putin would be clearly and openly signaling that a NATO-Russia war is exactly what is about to happen—with all its potential nuclear implications—if NATO, the United States, and Ukraine do not change course. The demands would clearly be a cessation of military aid to Ukraine, Ukraine comes to the negotiating table with neutrality in hand, and the West reduces the economic punishment against the Russian economy.

The second pathway, call it “Putin Emboldened,” sees Putin assessing that the use of tactical nuclear weapons in Ukraine carries with it less cost and risk than previously believed and that their use is a viable way to militarily end the conflict. Without an escalatory response, Putin may believe that NATO and the United States are deterred from entering the conflict and that a window is open to use additional non-strategic nuclear weapons, with the goal of destroying Ukraine’s ability to defend itself. Putin essentially comes away from the lack of a symmetrical response believing that NATO’s willingness to use nuclear weapons is less robust than its military posture or doctrine might have otherwise suggested. In thinking about the US and NATO response to “Putin Emboldened,” it is hard to imagine both standing by as Russia repeatedly uses nuclear weapons in Ukraine, and so it is difficult to see this scenario not also leading to a NATO-Russia conflict.

Staying the course entails less confidence in predicting the response by Putin. Whether pushed into a corner or believing nuclear use is less costly, the conflict likely will likely escalate beyond Ukraine. This may be unavoidable to policymakers, given the need to continue assistance to Ukraine and undermine the belief that the use of nuclear weapons, in a scenario like the Ukraine war, is acceptable with little to no costs.

Push for settlement. Given the consequences of a nuclear war between the United States, NATO, and Russia and the risk of escalation beyond Ukraine should the conflict continue, this option argues for ending the conflict in some way that gives the Russian leadership an “out” from the conflict. While seemingly reasonable given the level of destruction and costs of escalation, this option has significant challenges and implications for the international security environment.

The central challenge to this option is the lack of overlapping interests and positions in a negotiated settlement between the Russians and Ukrainians. From the Russian perspective, a negotiated settlement would entail ceasing security cooperation between Ukraine and the United States and NATO, neutrality of Ukraine, and the acceptance of Russian possession of Crimea and the Donbass, along with a host of other security assurances favorable to the Russian government. Given the Ukrainian success in defending their country thus far, this does not seem politically feasible or desirable from the perspective of the Ukrainian leadership.

For the United States and NATO to push the Ukrainian government to negotiate for a position that Ukraine believes is contrary to its core interests, the United States and NATO would need to force the Ukrainian government to the negotiating table by threatening to abandon support for Ukraine. This does not seem politically feasible given the current support and solidarity in the West. But more important, it would signal that nuclear blackmail is effective. Coercion by the United States and NATO against Ukraine to force a negotiated settlement would be tantamount to a 180-degree shift in policy because of Russia’s use of nuclear weapons in Ukraine. This would set an extremely dangerous precedent going forward, not only for Russia but for other world actors, especially in the Asian-Pacific, that could see a low cost of using nuclear weapons as an argument for them playing a greater role in pursuing their own geopolitical goals.

If Putin decides to use nuclear weapons in Ukraine, it will represent an unparalleled level of barbarity and an eschewing of international norms. It will also present NATO and the United States with complicated policy options, all of which have potential global consequences. I have attempted to lay out a broad framework for potential policy responses. I argue that the two extremes, responding in kind and pushing for a settlement, are unwise given the escalatory risks or potential for establishing destructive and unstable patterns of behavior. The two other options—escalating conventionally against Russia or staying the course—each have their own risks and levels of uncertainty. Except for bending to nuclear coercion, it is difficult to see how Russia’s use of nuclear weapons in Ukraine does not significantly raise the possibility of a conflict between Russia and NATO.