Updated at 11:30 a.m. ET on June 21, 2022
The 12th Main Directorate of the Russian Ministry of Defense operates a dozen central storage facilities for nuclear weapons. Known as “Object S” sites and scattered across the Russian Federation, they contain thousands of nuclear warheads and hydrogen bombs with a wide variety of explosive yields. For the past three months, President Vladimir Putin and other Russian officials have been ominously threatening to use nuclear weapons in the war against Ukraine. According to Pavel Podvig, the director of the Russian Nuclear Forces Project and a former research fellow at the Moscow Institute of Physics and Technology, now based in Geneva, the long-range ballistic missiles deployed on land and on submarines are Russia’s only nuclear weapons available for immediate use. If Putin decides to attack Ukraine with shorter-range, “tactical” nuclear weapons, they will have to be removed from an Object S site—such as Belgorod-22, just 25 miles from the Ukrainian border—and transported to military bases. It will take hours for the weapons to be made combat-ready, for warheads to be mated with cruise missiles or ballistic missiles, for hydrogen bombs to be loaded on planes. The United States will most likely observe the movement of these weapons in real time: by means of satellite surveillance, cameras hidden beside the road, local agents with binoculars. And that will raise a question of existential importance: What should the United States do?
President Joe Biden has made clear that any use of nuclear weapons in Ukraine would be “completely unacceptable” and “entail severe consequences.” But his administration has remained publicly ambiguous about what those consequences would be. That ambiguity is the correct policy. Nevertheless, there must also be open discussion and debate outside the administration about what is really at stake. During the past month, I’ve spoken with many national-security experts and former government officials about the likelihood of Russia using nuclear weapons against Ukraine, the probable targets, and the proper American response. Although they disagreed on some issues, I heard the same point again and again: The risk of nuclear war is greater today than at any other time since the Cuban missile crisis. And the decisions that would have to be made after a Russian nuclear strike on Ukraine are unprecedented. In 1945, when the United States destroyed two Japanese cities with atomic bombs, it was the world’s sole nuclear power. Nine countries now possess nuclear weapons, others may soon obtain them, and the potential for things going terribly wrong has vastly increased.
Several scenarios for how Russia might soon use a nuclear weapon seem possible: (1) a detonation over the Black Sea, causing no casualties but demonstrating a resolve to cross the nuclear threshold and signaling that worse may come, (2) a decapitation strike against the Ukrainian leadership, attempting to kill President Volodymyr Zelensky and his advisers in their underground bunkers, (3) a nuclear assault on a Ukrainian military target, perhaps an air base or a supply depot, that is not intended to harm civilians, and (4) the destruction of a Ukrainian city, causing mass civilian casualties and creating terror to precipitate a swift surrender—the same aims that motivated the nuclear attacks on Hiroshima and Nagasaki.
Any response by the Biden administration would be based not only on how Russia uses a nuclear weapon against Ukraine but also, more important, on how Russia’s future behavior might be affected by the American response. Would it encourage Putin to back down—or to double down? Cold War debates about nuclear strategy focused on ways to anticipate and manage the escalation of a conflict. During the early 1960s, Herman Kahn, a prominent strategist at the Rand Corporation and the Hudson Institute, came up with a visual metaphor for the problem: “the escalation ladder.” Kahn was one of the primary inspirations for the character Dr. Strangelove in Stanley Kubrick’s classic 1964 film, and yet the escalation ladder remains a central concept in thinking about how to fight a nuclear war. Kahn’s version of the ladder had 44 steps. At the bottom was an absence of hostilities; at the top was nuclear annihilation. A president might choose to escalate from step No. 26, “Demonstration Attack on Zone of Interior,” to step No. 39, “Slow-Motion Countercity War.” The goal of each new step upward might vary. It might simply be to send a message. Or it could be to coerce, control, or devastate an adversary. You climbed the ladder to reach the bottom again someday.
The “escalation vortex” is a more recent and more complex visualization of a potential conflict between nuclear states. It was developed by Christopher Yeaw, who served as chief scientist at the U.S. Air Force Global Strike Command from 2010 to 2015. In addition to the vertical aspects of the escalation ladder, the vortex incorporates horizontal movement among various domains of modern warfare—space, cyber, conventional, nuclear. An escalation vortex looks like a tornado. An illustration of one, featured in a Global Strike Command slideshow, places the worst outcome at the widest part of the funnel: “the absolute highest levels of permanent societal destruction.”
In October 1962, Sam Nunn was a 24-year-old recent graduate from Emory University School of Law who’d just gotten a security clearance and a job as a staff member for the House Armed Services Committee. When a colleague backed out of an overseas tour of NATO bases, Nunn took his place, left the United States for the first time—and wound up at Ramstein Air Base, in Germany, at the height of the Cuban missile crisis. Nunn remembers seeing NATO fighters parked near runways, each loaded with a single hydrogen bomb, ready to fly toward the Soviet Union. Pilots sat in chairs beside their planes, day and night, trying to get some sleep while awaiting the order to take off. They had only enough fuel for a one-way mission and planned to bail out somewhere, somehow, after dropping their bombs. The commander of the U.S. Air Force in Europe told Nunn that if a war began, his pilots would have to get their planes off the ground within a few minutes; Ramstein Air Base would be one of the first NATO targets destroyed by a Soviet nuclear attack. The commander kept a walkie-talkie with him at all times to give the takeoff order.
The Cuban missile crisis left a strong impression on Nunn. During his 24 years as a United States senator, he worked tirelessly to reduce the risk of nuclear war and nuclear terrorism. As the head of the Senate Armed Services Committee, he championed close cooperation with Moscow on nuclear matters. To continue those efforts, he later co-founded a nonprofit, the Nuclear Threat Initiative, with which I have collaborated on a number of projects. All of that work is now at risk of being undone by Russia’s invasion of Ukraine and the strident nuclear rhetoric accompanying it.
Before the attack on Ukraine, the five nations allowed to have nuclear weapons by the Non-Proliferation Treaty (NPT)—the United States, the United Kingdom, Russia, China, and France—had reached agreement that the use of such weapons could be justified only as a purely defensive measure in response to a nuclear or large-scale conventional attack. In January 2022, those five countries issued a joint statement affirming Ronald Reagan’s dictum that “a nuclear war must never be fought and can never be won.” A month later, Russia violated norms that had prevailed under the NPT for more than half a century. It invaded a country that had given up nuclear weapons; threatened nuclear attacks against anyone who tried to help that country; and committed acts of nuclear terrorism by shelling the reactor complexes at Chernobyl and Zaporizhzhya.
Nunn supports the Biden administration’s strategy of “deliberate ambiguity” about how it would respond to Russia’s use of a nuclear weapon. But he hopes that some form of back-channel diplomacy is secretly being conducted, with a widely respected figure like former CIA Director Robert Gates telling the Russians, bluntly, how harshly the United States might retaliate if they cross the nuclear threshold. During the Cuban missile crisis, President John F. Kennedy and First Secretary Nikita Khrushchev both wanted to avoid an all-out nuclear war—and still almost got one, because of misunderstandings, miscommunications, and mistakes. Back-channel diplomacy played a crucial role in ending that crisis safely.
Nunn describes Russia’s violations of long-standing norms as “Putin’s nuclear folly” and stresses that three fundamental things are essential for avoiding a nuclear catastrophe: rational leaders, accurate information, and no major blunders. “And all three are now in some degree of doubt,” he says.
If Russia uses a nuclear weapon in Ukraine, Nunn thinks that an American nuclear retaliation should be the last resort. He favors some sort of horizontal escalation instead, doing everything possible to avoid a nuclear exchange between Russia and the United States. For example, if Russia hits Ukraine with a nuclear cruise missile launched from a ship, Nunn would advocate immediately sinking that ship. The number of Ukrainian casualties should determine the severity of the American response—and any escalation should be conducted solely with conventional weapons. Russia’s Black Sea fleet might be sunk in retaliation, and a no-fly zone could be imposed over Ukraine, even if it meant destroying anti-aircraft units on Russian soil.
Since the beginning of the invasion, Russia’s nuclear threats have been aimed at discouraging the United States and its NATO allies from providing military supplies to Ukraine. And the threats are backed by Russia’s capabilities. Last year, during a training exercise involving about 200,000 troops, the Russian army practiced launching a nuclear assault on NATO forces in Poland. “The pressure on Russia to attack the supply lines from NATO countries to Ukraine will increase, the longer this war continues,” Nunn says. It will also increase the risk of serious blunders and mistakes. An intentional or inadvertent Russian attack on a NATO country could be the beginning of World War III.
During the summer of 2016, members of President Barack Obama’s national-security team secretly staged a war game in which Russia invades a NATO country in the Baltics and then uses a low-yield tactical nuclear weapon against NATO forces to end the conflict on favorable terms. As described by Fred Kaplan in The Bomb (2020), two groups of Obama officials reached widely divergent conclusions about what the United States should do. The National Security Council’s so-called Principals Committee—including Cabinet officers and members of the Joint Chiefs of Staff—decided that the United States had no choice but to retaliate with nuclear weapons. Any other type of response, the committee argued, would show a lack of resolve, damage American credibility, and weaken the NATO alliance. Choosing a suitable nuclear target proved difficult, however. Hitting Russia’s invading force would kill innocent civilians in a NATO country. Striking targets inside Russia might escalate the conflict to an all-out nuclear war. In the end, the NSC Principals Committee recommended a nuclear attack on Belarus—a nation that had played no role whatsoever in the invasion of the NATO ally but had the misfortune of being a Russian ally.
Deputy staff members at the NSC played the same war game and came up with a different response. Colin Kahl, who at the time was an adviser to Vice President Biden, argued that retaliating with a nuclear weapon would be a huge mistake, sacrificing the moral high ground. Kahl thought it would be far more effective to respond with a conventional attack and turn world opinion against Russia for violating the nuclear taboo. The others agreed, and Avril Haines, a deputy national security adviser, suggested making T-shirts with the slogan Deputies should run the world. Haines is now President Biden’s Director of National Intelligence, and Kahl is the Under Secretary of Defense for Policy.
In 2019, the Defense Threat Reduction Agency (DTRA) ran extensive war games on how the United States should respond if Russia invades Ukraine and then uses a nuclear weapon there. DTRA is the only Pentagon agency tasked exclusively with countering and deterring weapons of mass destruction. Although the results of those DTRA war games are classified, one of the participants told me, “There were no happy outcomes.” The scenarios for nuclear use were uncannily similar to the ones being considered today. When it comes to nuclear warfare, the participant said, the central message of the 1983 film WarGames still applies: “The only winning move is not to play.”
None of the national-security experts I interviewed thought the United States should use a nuclear weapon in response to a Russian nuclear attack on Ukraine. Rose Gottemoeller—who served as the chief American negotiator of the New START arms-control treaty with Russia and later as the deputy secretary general of NATO—believes that any nuclear attack on Ukraine would inspire global condemnation, especially from countries in Africa and South America, continents that are nuclear-weapon-free zones. She thinks that China, despite its tacit support for the invasion of Ukraine, would strongly oppose Putin’s use of a nuclear weapon and would back sanctions against Russia at the United Nations Security Council. China has long supported “negative nuclear assurances” and promised in 2016 “unconditionally not [to] use or threaten to use nuclear weapons against non-nuclear-weapon states or in nuclear-weapon-free zones.”
If the United States detects tactical weapons being removed from Russian storage sites, Gottemoeller thinks the Biden administration should send a tough warning to Moscow through back channels—and then publicize the movement of those weapons, using the same tactic of openly sharing intelligence that seemed to thwart Russian false-flag operations involving chemical and biological weapons in Ukraine. Over the years, she’s gotten to know many of the top commanders who oversee Russia’s nuclear arsenal and developed great respect for their professionalism. Gottemoeller says they might resist an order to use nuclear weapons against Ukraine. And if they obey that order, her preferred option would be “a muscular diplomatic response” to the nuclear strike, not a nuclear or conventional military response, combined with some form of hybrid warfare. The United States could launch a crippling cyberattack on the Russian command-and-control systems tied to the nuclear assault and leave open the possibility of subsequent military attacks.
Scott Sagan, a co-director of the Center for International Security and Cooperation, at Stanford University, believes that the risk of Russia using a nuclear weapon has declined in the past month, as the fighting has shifted to southern Ukraine. Putin is unlikely to contaminate territory he’s hoping to seize with radioactive fallout. And a warning shot, such as the detonation of a nuclear weapon harmlessly over the Black Sea, would serve little purpose, Sagan says. It would signal irresolution, not resolve—a conclusion that the United States reached half a century ago about the potential utility of a NATO demonstration strike to deter the Red Army. Sagan concedes that if Russia were to lose major battles in the Donbas, or if a Ukrainian counteroffensive seemed on the verge of a great victory, Putin might well order the use of a nuclear weapon to obtain a surrender or a cease-fire. In response, depending on the amount of damage caused by the nuclear explosion, Sagan would advocate American conventional attacks on Russian forces in Ukraine, Russian ships in the Black Sea, or even military targets inside Russia, such as the base from which the nuclear strike was launched.
Sagan takes issue with how the back-and-forth of military conflict is commonly depicted. As an image, an escalation ladder seems too static. It suggests the freedom to decide whether you should go up or down. Sagan thinks nuclear escalation would be more like an escalator: Once it starts moving, it has a momentum of its own, and it’s really hard to get off. He would be deeply concerned by any sign that Putin is taking even the initial steps toward nuclear use. “We should not underestimate the risk of an accidental nuclear detonation if tactical weapons are removed from their storage igloos and dispersed widely among Russian military forces,” Sagan warns.
I recently had lunch with former Secretary of Defense William J. Perry at his home in Palo Alto, California. Perry is 94 years old, one of the last prominent military strategists active today who witnessed firsthand the devastation of the Second World War. He served in the U.S. Army of Occupation of Japan, and nothing that he had read about the firebombing of Tokyo prepared him for what he saw there—a great city burned to the ground, the survivors living amid fused rubble, dependent on military rations. In Naha, the capital of Okinawa, the destruction seemed even worse. In his memoir, Perry writes that not a building was left standing, and includes a famous description: “The lush tropical landscape was turned into a vast field of mud, lead, decay, and maggots.” What Perry saw in Japan left him profoundly unsettled by the nuclear threat. Naha and Tokyo had been devastated by tens of thousands of bombs dropped in hundreds of air raids; Hiroshima and Nagasaki, by a single atomic bomb each.
Perry later earned advanced degrees in mathematics and became an early Silicon Valley pioneer, specializing in satellite surveillance and the use of digital technology for electronic warfare. During the Cuban missile crisis, he traveled to Washington, D.C., at the request of the CIA, and scrutinized satellite photographs of Cuba for evidence of Soviet nuclear weapons. He helped prepare the morning intelligence reports for President Kennedy and wondered every night whether the next day would be his last. As an undersecretary of defense during the Carter administration, Perry played a crucial role in developing stealth technology, and as secretary of defense during the Clinton administration, he led the effort to lock up nuclear weapons and fissile material at locations throughout the former Soviet Union. After leaving the Pentagon, he earned a dovish reputation, joining Sam Nunn, Henry Kissinger, and George Shultz in 2008 in a plea for the abolition of nuclear weapons; opposing American plans for new ground-based, long-range ballistic missiles; and calling upon the United States to make a formal declaration that it would never be the first to launch a nuclear attack. But Perry’s views on the Russian invasion of Ukraine are anything but warm and fuzzy.
We ate sandwiches that Perry had prepared, with bread he’d baked, sitting on a large terrace where the planters overflowed with flowers and hummingbirds hovered at feeders, beneath a brilliant blue sky. The setting could not have been more bucolic, the idea of nuclear war more remote. A few days earlier, Perry had given a speech at Stanford, outlining what was at stake in Ukraine. The peace that had reigned in Europe for almost eight decades had been shattered on February 24, he said, and “if Russia’s invasion is successful, we should expect to see other invasions.” Putin was now engaging in blackmail, threatening to use nuclear weapons for offensive, not defensive, purposes, trying to deter the United States from providing the conventional weapons that Ukraine badly needs. “I fear that if we give in to this outrageous threat,” Perry said, “we will face it again.”
Perry’s manner is thoughtful, calm, and gentle, not the least bit alarmist or overemotional. I’ve known him for more than a decade, and though his voice has grown softer, his mind is remarkably undimmed, and beneath his warmth and kindness lies steel. Perry has met Putin on a number of occasions, dating back to when he was the deputy mayor of St. Petersburg—and thinks Putin will use tactical weapons in Ukraine if it seems advantageous to do so. Although the Russian Federation’s declared policy is to use nuclear weapons only when confronted with an existential threat to the state, public declarations from Moscow should always be taken with a grain of salt. The Soviet Union adamantly denied having any missile bases in Cuba as it was building them. It publicly vowed for years never to be the first to use a nuclear weapon, while secretly adopting war plans that began with large-scale nuclear attacks on NATO bases and European cities. The Kremlin denied having any intention to invade Ukraine, right up until it invaded Ukraine. Perry always found Putin to be competent and disciplined, but cold. He believes that Putin is rational at the moment, not deranged, and would use nuclear weapons in Ukraine to achieve victory and thereby ensure the survival of his regime.
During the Cold War, the United States based thousands of low-yield tactical nuclear weapons in NATO countries and planned to use them on the battlefield in the event of a Soviet invasion. In September 1991, President George H. W. Bush unilaterally ordered all of America’s ground-based tactical weapons to be removed from service and destroyed. Bush’s order sent a message that the Cold War was over—and that the United States no longer considered tactical weapons to be useful on the battlefield. The collateral damage they would cause, the unpredictable patterns of lethal radioactive fallout, seemed counterproductive and unnecessary. The United States was developing precision conventional weapons that could destroy any important target without breaking the nuclear taboo. But Russia never got rid of its tactical nuclear weapons. And as the strength of its conventional military forces waned, it developed very low-yield and ultra low-yield nuclear weapons that produce relatively little fallout. In the words of a leading Russian nuclear-weapons designer, they are “environmentally conscious.” The more than 100 “peaceful nuclear explosions” conducted by the Soviet Union—ostensibly to obtain knowledge about using nuclear devices for mundane tasks, like the excavation of reservoirs—facilitated the design of very low-yield tactical weapons.
Two nuclear detonations have already occurred in Ukraine, as part of the Soviet Union’s “Program No. 7—Peaceful Explosions for the National Economy.” In 1972, a nuclear device was detonated supposedly to seal a runaway gas well at a mine in Krasnograd, about 60 miles southwest of Kharkiv. The device had an explosive force about one-quarter as large as that of the atomic bomb that destroyed Hiroshima. In 1979, a nuclear device was detonated for the alleged purpose of eliminating methane gas at a coal mine near the town of Yunokommunarsk, in the Donbas. It had an explosive force about one-45th as large as that of the Hiroshima bomb. Neither the workers at the mine nor the 8,000 residents of Yunokommunarsk were informed about the nuclear blast. The coal miners were given the day off for a “civil-defense drill,” then sent back to work in the mine.
The weakness of Russia’s conventional forces compared with those of the United States, Perry suggests, and Russia’s relative advantage in tactical weapons are factors that might lead Putin to launch a nuclear attack in Ukraine. It would greatly benefit Russia to establish the legitimacy of using tactical nuclear weapons. To do so, Putin must choose the right target. Perry believes that a demonstration strike above the Black Sea would gain Putin little; the destruction of a Ukrainian city, with large civilian casualties, would be a tremendous mistake. But if Russia can destroy a military target without much radioactive fallout, without civilian casualties, and without prompting a strong response from the United States, Perry says, “I don’t think there’s a big downside.” Russia has more nuclear weapons than any other nation in the world. Its national pride is strongly linked to its nuclear weapons. Its propagandists celebrate the possible use of nuclear weapons—against Ukraine, as well as against the United States and its NATO allies—on an almost daily basis, in an attempt to normalize their use. Its military has already destroyed Ukrainian cities, deliberately targeted hospitals, killed thousands of civilians, countenanced looting and rape. The use of an ultra low-yield nuclear weapon against a purely military target might not seem too controversial. “I think there would be an international uproar, but I don’t think it would last long,” Perry says. “It might blow over in a week or two.”
If the United States gets intelligence that Russia is preparing to use a nuclear weapon, Perry believes that the information should be publicized immediately. And if Russia uses one, the United States should call for international condemnation, create as big a ruckus as possible—stressing the word nuclear—and take military action, with or without NATO allies. The reprisal should be strong and focused and conventional, not nuclear. It should be confined to Ukraine, ideally with targets linked to the nuclear attack. “You want to go as little up the escalation ladder as you can get away with doing and still have a profound and relevant effect,” Perry says. But if Putin responds by using another nuclear weapon, “you take off the gloves the second time around” and perhaps destroy Russia’s military forces in Ukraine, which the United States could readily do with conventional weapons. Perry realizes that these escalations would be approaching the kind of Dr. Strangelove scenarios that Herman Kahn wrote about. But if we end up fighting a war with Russia, that would be Putin’s choice, not ours.
Perry has been warning for many years that the nuclear danger is growing. The invasion of Ukraine has unfortunately confirmed his prediction. He believes that the odds of a full-scale nuclear war were much higher during the Cuban missile crisis, but that the odds of a nuclear weapon being used are higher now. Perry doesn’t expect that Russia will destroy a Ukrainian air base with a tactical weapon. But he wouldn’t be surprised. And he hopes the United States will not be self-deterred by nuclear blackmail. That would encourage other countries to get nuclear weapons and threaten their neighbors.
As I listened to the recording of my conversation with Bill Perry, it was filled with the incongruous sounds of wind chimes and birds singing. Vladimir Putin can determine if, when, and where a nuclear attack occurs in Ukraine. But he cannot control what happens after that. The consequences of that choice, the series of events that would soon unfold, are unknowable. According to The New York Times, the Biden administration has formed a Tiger Team of national-security officials to run war games on what to do if Russia uses a nuclear weapon. One thing is clear, after all my discussions with experts in the field: We must be ready for hard decisions, with uncertain outcomes, that nobody should ever have to make.
This article has been modified to reflect a clarification by Sam Nunn regarding his views on America’s possible nuclear response to Russian use of nuclear weapons in Ukraine.