Save for later Print Download Share LinkedIn Twitter Largely absent since the end of the Cold War three decades ago, fears of a nuclear Armageddon have been rekindled by the war in Ukraine, with Russian President Vladimir Putin putting his nuclear forces on "a special regime of combat duty.” This may be just posturing — a warning to the West to back off. But Russian use of a tactical nuclear weapon on the battlefield in Ukraine can't be ruled out. That need not necessarily escalate to all-out nuclear war, depending on the West's response. However, use of nuclear weapons even on a "limited" scale would greatly increase the potential for miscalculation and a full-blown nuclear conflict. Little more than 30 years ago, a stunning set of events unfolded — the fall of the Berlin Wall, the signing of the first Strategic Arms Reduction Treaty (Start I) between the Soviet Union and the US, and in December 1991, the dissolution of the Soviet Union. The Cold War was over, and generations who had grown up in its shadow breathed a collective sigh of relief. Three years later, in an evolving spirit of openness, then-US Energy Secretary Hazel O'Leary surprised the world again when she invited journalists, including from overseas, to tour Pantex, the sole remaining plant for "final assembly" of America's nuclear weapons, near Amarillo, Texas. I was one of them.Around this vast, mostly underground complex in the treeless expanse of the Texas Panhandle, politically conservative ranchers who lived around Pantex invited me into their homes. They’d been fighting further government encroachment on their land, and environmental and health problems associated with the plant; they wanted people to know about it. Underground at the plant the situation was different: Workers accustomed to decades of secrecy and facing life-threatening dangers in the work they did — which at that point was disassembling weapons built over the preceding decades — weren’t happy about the visitors with notebooks. “The trust the government has in Russia isn’t shared here,” one confided in me. “Most of us think we’ll be back building them [warheads] in a few years.” His forecast proved prescient even if the timeline was off. Nuclear Forces on Combat DutySome 28 years later, on Feb. 27 of this year, Putin declared that Russia’s nuclear forces would begin "a special regime of combat duty” — just three days after he ordered his premeditated assault on Ukraine. This rekindled fears of nuclear devastation at a level unknown to the world since the 1962 Cuban Missile Crisis. It also sparked spirited discussions as to how the West should respond if Putin actually uses nuclear weapons in Ukraine. “I think we have to start from the presumption that he would welcome the opportunity to use nuclear weapons," said Gen. (Ret.) Wesley Clark during an Atlantic Council webinar Mar. 15. "He wants to show his determination. He wants to intimidate the West. He thinks he has a nuclear advantage.”Certainly, Putin's order was a warning for US and Nato forces to back off. Rose Gottemoeller, former undersecretary for arms control in the Obama administration, said that in recent talks Russian experts explained that Putin's order would bring "an extra three to six people" to nuclear command posts normally manned with about six. The locations and numbers of these posts is not publicly known. She added, "The Russians have told us that they have made no changes thus far in the operational status of their missiles per se, and I don't have any reason not to believe that."Hans Kristensen, director of the Nuclear Information Project with the Federation of American Scientists, has closely followed satellite imagery since Putin’s statement, and said that if Russia planned an attack it would be detectable — mobile intercontinental ballistic missiles (ICBMs) would be moved out into forests, strategic bombers would be loaded with warheads and nuclear submarines not already deployed would put out to sea. Warheads for tactical nuclear weapons would have to be transported from bunkers to wherever the launchers were. “None of that has happened,” Kristensen added. Putin’s nuclear order "was a strategic warning to the US and Nato to stay out.”It's worth noting that six US F-35s and a B-52, on orders from US President Joe Biden, arrived on Nato's eastern front Feb. 24, the day the invasion started, and the nuclear-capable B-52 flew over the Black Sea with Polish fighters, in what appeared to be a signaling operation of their own by the US and Nato. Tactical Nuclear WeaponsNo one completely rules out the idea that Putin might lob a tactical nuclear weapon — or even more than one — into Ukraine or into the Black Sea with the aim of terrifying the Ukrainians into capitulating. Some think it entirely possible, given Russia’s superiority in such such lower-yield battlefield nuclear weapons. The prospects might worsen if the war expands beyond Ukraine. "It's really so unpredictable what Vladimir Putin will do and what his decision patterns are here," says Gottemoeller.The US has roughly 5,550 warheads and Russia has 6,255. But the composition of their nuclear forces is different, particularly when it comes to tactical nuclear weapons, of which Russia is believed to have some 1,000-2,000. They vary widely, from surface-to-air missiles to torpedoes, depth charges and short-range army missiles. The US once had thousands of tactical nuclear weapons on surface ships and attack submarines, but they were completely phased out “just like the Army has been completely denuclearized. We used to have nuclear artillery. We don’t have that anymore,” says Kristensen. The end of the Cold War catalyzed new thinking about deterrence. The US military concluded it didn't need nuclear on the battlefield because modern conventional weapons could be even more effective in that context. Should nuclear ever be required in a dire situation, higher-yield, longer-range strategic weapons could do the job in overwhelming fashion, the thinking went. This strategy is reflected in Nato’s nuclear deterrent today — long on strategic, but short on tactical, with only nuclear-capable fighter planes for delivery left in Europe. The US is embarked on a multidecade program — with a current estimated total price tag of some $2 trillion over the next 30 years — to sustain and modernize its strategic nuclear weapons launched from air, sea or land. The disparity between the US and stronger Russian tactical nuclear capability is what makes Clark believe that Putin "thinks he has some nuclear superiority. This is the danger." Clark also believes that Putin thinks Russia "is better prepared to ride out a nuclear exchange than the US." Matthew Kroenig, deputy director of the Atlantic Council's Scowcroft Center of Strategy and Security, agrees that Russia's tactical superiority is "part of the reason that the threat is real and that I think Putin would find this as potentially an attractive option." Conventional ComebacksThis view is not shared universally among the US military or nuclear arms experts; nor is it clear why for Putin this would be an attractive option, given that he could be facing a variety of possibly superior military response options. The "intensity" of Nato's response is key, says Kristensen. “It could either be fighter jets delivering tactical nuclear bombs or more likely a very limited strike from a B-52 with a long-range nuclear cruise missile” — albeit one still classified as tactical. Or the US and its Nato allies could choose to retaliate not with nuclear but with advanced conventional weapons.Historian Christopher Preble, also associated with the Scowcroft Center, voiced skepticism about Putin introducing nuclear weapons. “How confident is Vladimir Putin that the use of a tactical nuclear weapon won't result in the US and Nato waging a war against him?" He added, "I don't know why he would have that confidence. In fact, I think if anything, he would expect a disproportionate response to the use of even a single tactical nuclear weapon.” Complicating the issue of Biden's possible response to any introduction of nuclear weapons is the fact that Ukraine is a non-Nato country. "Biden said he's not going to get involved militarily. Presumably he meant that to apply even if Putin uses nuclear weapons," said Kroenig. "My prediction is that if this happened, the Biden administration would fight through without retaliating with nuclear weapons."If he's wrong and Biden does retaliate, would he go nuclear and risk an all-out conflict? Unlikely, says Clark. "No one in America wants to confront the idea of a nuclear effort," he said, "It would mean immediately Biden would go to zero percent in the polls."Alternatively, if he used conventional weapons, either in Ukraine or, in an escalated conflict, a Nato country, there is a danger that Biden could encourage other states to launch nuclear attacks without fear of a US nuclear reprisal. But avoiding a tit-for-tat nuclear response could also gain him the moral high ground and — especially if the response proved successful — demonstrate that nuclear isn't the only way to go even in a situation involving nuclear weapons. Either way, if Putin introduces nuclear weapons on a “limited” basis he raises the risk factor, already very high, and increases the potential for miscalculation and a full-blown nuclear war. “It’s a dangerous illusion that nuclear weapons can be used on the battlefield and the conflict can be kept limited,” says Daryl Kimball, head of the Washington-based Arms Control Association, who points out that Russia is under no military threat from Nato or Ukraine.And when it’s all over, the risks will remain. Of the eight or so arms control treaties signed since the Strategic Arms Limitation Talks (Salt) began in 1969, only one remains — New Start, which limits the number of deployed strategic warheads on each side to 1,550. That treaty provides an “important node of transparency,” says Kristensen, who counts 328 on-site inspections and 23,100 notifications by both sides since the agreement entered into force in 2018. The treaty expires on Feb. 4, 2026, which is little more than a long weekend away in the timescales of fraught arms control negotiations.Stephanie Cooke is editor of Nuclear Intelligence Weekly and author of In Mortal Hands: A Cautionary History of the Nuclear Age.