Vladimir Putin has repeatedly threatened to escalate the war in Ukraine by breaking the nuclear taboo. In June, as Russia installed tactical nuclear weapons in Belarus, he raised the spectre of a Third World War. And that was before the Wagner mutiny destabilised his position.
Western officials have been keen to emphasise that such a war may not transpire. Many suggest the risk of nuclear escalation has eased since the disastrous opening months of the invasion. In October, the German Institute for International and Security Affairs judged that Moscow’s use of its nuclear deterrent remained “careful”; others detect the restraining hand of China’s premier, Xi Jinping, in the Kremlin’s actions.
Even before the war, however, the established arms control framework had begun to fall apart. While some analysts conclude Russia would only use a nuclear weapon to deter existential threats to the homeland, there has been speculation that it might take a higher-stakes approach, “escalating to de-escalate”. Foreign Affairs magazine has suggested that this “could mean using a handful of tactical, low-yield nuclear weapons on the battlefield.” Veterans of the British defence establishment, including Peter Ricketts, life peer and the UK’s first national security adviser, suggested that if Ukraine’s counter-offensive were to bring them close to recapturing Crimea—“a humiliation so complete that it would put into question Putin’s own personal survival”—that would be dangerous territory. After a long respite, the fear of nuclear conflict is back.
Following the Cold War, the complex, nuanced theology of deterrence that had been nurtured in London and Washington largely fell away—just as, by 1998, the UK had abandoned the land- and air-based wings of its nuclear deterrent, leaving only Trident submarines. But since Russia annexed Crimea in 2014, the west has begun to revitalise this thinking. To make sense of how the Ukraine conflict might turn nuclear, experts in military and defence strategies on both sides of the Atlantic have returned to the foundational work of the 1950s and 1960s—not least one curious idea.
The “ladder of escalation” was the brainchild of an American strategist called Herman Kahn. In his book On Escalation (1965) Kahn presented a “generalised (or abstract) scenario” made up of 44 “rungs” that the world might climb to pass from crisis to Armageddon. Lawrence Freedman, historian and author of The Evolution of Nuclear Strategy, notes that the ladder offers “almost thirty distinct ways of using nuclear weapons following their first use at rung fifteen”. Kahn’s conceit was to explode the idea that “escalation” would be an unstoppable rush to disaster; rather, the opening stages of a nuclear war might progress incrementally. The ladder, Freedman says, “is a very powerful metaphor”, which remains influential.
This certainly seems so in the United States. Daniel Post is a veteran of US Strategic Command, where he was involved in training and practising for using nuclear weapons; he is now a military professor at the US Naval War College, where military leaders are taught strategy and wartime decision-making. He argues that the literature of escalation dynamics is “not as fully developed as some other areas of international relations”, and that while its ideas are somewhat dated, On Escalation has its uses. Peter Scoblic, author of US and Them: Conservatism in the Age of Nuclear Terror, has found its approach useful, not least in countering panicky online reactions to the invasion of Ukraine.
When I raise Kahn with Admiral James Stavridis, Nato’s supreme allied commander in Europe from 2009 to 2013, he tells me: “I constantly try to consider the dangers of vertical escalation.” He adds that the ideas of Kahn are “central to the plot” of his co-authored novel, 2034: A Novel of the Next World War, which ends with strategic nuclear attacks on cities. In Ukraine, he suggests, “we should be mindful of how easy it would be to have such escalation should Putin choose to use a tactical nuclear weapon.”
So is the ladder of escalation a useful tool? Or, as others fear, does it embody a dangerous delusion? That partly depends on what you make of the man who invented it.
In 1947, two years after the US first used its new atom bombs against Japan, a youthful Herman Kahn landed a job with a new US Air Force-affiliated thinktank, the Rand Corporation. From its base in Santa Monica, California, Rand’s new cadre of civilian scientists and strategists was leading the transformation of “war” into something beyond the comprehension of the public, even the generals.
Kahn began as a physicist, working on weapons design, but as Scoblic puts it, he realised that understanding nuclear conflict required “the embrace of imagination”. He turned to newer, more creative fields of study, such as “systems analysis”. As his biographer Sharon Ghamari-Tabrizi writes in The Worlds of Herman Kahn: The Intuitive Science of Thermonuclear War, his science became “science fiction, an exercise that derived political and military policy… from the vagaries of simulations concocted with good guesses.”
It’s unlikely Kahn would have taken this as a criticism. Science fiction was not only one of his childhood enthusiasms, but integral to how he thought. He is widely said to have been the inspiration for the crazed scientist in Stanley Kubrick’s 1964 movie Dr Strangelove; he happily engaged with the director and his satire. By the end of the 1950s he had risen to infamy, when it appeared that the Soviet Union’s nuclear armament programme was catching up with America’s. In fizzing, jokey lectures and then an incendiary book, On Thermonuclear War (1960), he shocked Americans with the conclusion of his imaginative efforts: that nuclear war was not unthinkable. He had thought about it, and it could be fought, and won. As Ghamari-Tabrizi tells me, he would confront audiences with the enormity of the moral choices involved by asking them how many people’s lives they were willing to risk to guard America against surprise nuclear attack. He was denounced as callous—at one point even compared to Nazi official Adolf Eichmann—but mounted a defence of himself in another book, Thinking About the Unthinkable (1962).
To his critics, “unthinkable” was a euphemism for “intolerable”: how could any decent person coolly discuss the destruction of tens of millions of their fellow human beings? But there was another criticism: Kahn was thinking about the unknowable. He was proposing to use imagination—through war games, models, simulations, scenarios—to be “realistic” about how nuclear war might unfold.
Ghamari-Tabrizi quotes the unimpressed reaction of the ex-chair of America’s Atomic Energy Commission, who thought Kahn and his fellow analysts were absurd to claim “that they can find answers… to what cannot be finally and firmly answered at all: the unimaginable complex and shifting human problems involved in the threat of nuclear warfare”. Kahn’s view was that “it has usually been lack of imagination, rather than excess of it, that caused unfortunate decisions and missed opportunities.”
In On Thermonuclear War (1960), even the ever-optimistic Kahn wrote about escalation as though it would likely be uncontrollable. But by the time he published On Escalation five years later, the world had weathered the Cuban Missile Crisis. This suggested that it was possible, particularly early on, to manage a nuclear confrontation step by step. Hence his imaginary ladder.
Kahn writes of ‘serious nuclear warfare’ as though there were another sort
Mixing his metaphors, Kahn has the ladder progress through a series of thresholds. The first three rungs are categorised as “Subcrisis Manoeuvring”—diplomatic gestures, solemn declarations. Then it escalates, via the “Don’t Rock the Boat Threshold” to a period of “Traditional Crisis”, from “Confrontation of Wills” (rung four) up to “Dramatic Military Confrontations” (rung nine). Clambering further, we cross the “Nuclear War is Unthinkable Threshold”, beyond which some of the rungs numbered 10 to 20—ultimatums, blockades—are reminiscent of what had lately played out between the superpowers over Cuba.
Kahn’s capacity to conceive of non-apocalyptic uses of nuclear weapons is jaw-dropping. This begins with something called “Barely Nuclear War” (rung 15), which he explains would “presumably” be “accepted as an accident or limited episode”. He writes of “serious nuclear warfare” as though there were another sort. He suggests that “if the balance of terror becomes sufficiently stable, and governments are believed to be under intense and graduated mutual deterrents”, even “exemplary attacks on population” might not trigger “an eruption to spasm or other central war”.
By rung 38, there has been an array of “counterforce” attacks—strategists’ jargon for smashing enemy missile silos. Even then, Kahn remains hopeful that so-called “countervalue” attacks—the destruction of cities—could be avoided. Part of the point of choosing a ladder as his metaphor was to suggest that tensions could not just go up, but come down.
If the situation in Ukraine is at rung 12 (“Large Conventional War”), does that tell us anything? Among those I spoke to for this article, I found broad agreement that the ladder should be handled warily. Freedman tells me it is “too neat” and that, detached from Kahn’s nuanced explanations, it can be “dangerously misleading”. Scoblic suggests that, given Kahn’s background at the “hyper-rationalist” Rand Corporation, some people take it too literally. Both point to Kahn’s own caveats: that, like any model, it simplifies and distorts. It is intended, Kahn protested, as a metaphor, a teaching aid, a “scenario generator”.
Kahn also suggested an alternative image, one emphasising the seven thresholds between his rungs: an elevator “in a department store with seven floors, each offering a number of options of varying intensity”. Though this sounds like the setting of a JG Ballard novel, it is perhaps better than the ladder at encapsulating how he thought escalation lurches upwards and where choices open up. Post, the veteran of US Strategic Command, points out that Kahn identified that there was a choice between fighting within the existing terms of battle and crossing a threshold, and notes that this realisation might clarify today’s dangers. “Increasing air sorties”, for example, is “not really escalation”, Post says, but if Russia “all of a sudden targets Nato supply dumps outside of Ukraine”, that would raise the conflict to a new level.
From here, Kahn formulates the concept of “escalation dominance”, which he defines as the “capacity, other things being equal, to enable the side possessing it to enjoy marked advantages in a given region of the escalation ladder”. Freedman notes this puts the onus on the disadvantaged opponent to decide whether to risk escalating. The danger to both sides is that they accept the challenge.
At least at the nuclear level, Kahn’s thinking seems more suited to the US, with its vast nuclear arsenal, than to countries like the UK. Kevin Tebbit, former permanent secretary at the Ministry of Defence, has been engaged in nuclear strategy thinking for decades. During the Cold War, when he was working for the British government’s nuclear guru, Michael Quinlan, they mocked Kahn’s ladder as “99 steps to Armageddon”; it was “completely unrealistic, complete bollocks,” Tebbit says.
All else aside, Tebbit points out that the British and French did not have “the capability to go through those phases”, whereas the US was equipped to do “the Herman Kahn sort of stuff”, first launching counterforce strikes, before deciding whether to target cities. The ladder’s plentiful options also raised a sensitive issue: would America choose to fight a so-called “tactical” nuclear war in Europe, avoiding the risk of escalation reaching the US itself? Unsurprisingly, European strategists have always discouraged this, in favour of equalising risk across Nato.
The principle on which Britain operated in the Cold War was altogether simpler than Kahn’s ladder. Its nuclear capability has been “declared… to the defence of the Alliance” since 1962. On the basis of “graduated flexible response”, Tebbit explains, a conventional attack by members of the Warsaw Pact would have been met in like terms—and if Nato territory were “in danger of being overrun, then we would reserve the right to escalate to the use of nuclear weapons”.
But this escalation was to be done on a fundamentally different basis than Kahn’s: the British rejected the notion that nuclear war was “winnable”. The strategy was to use a “theatre” nuclear weapon not as a means of attack per se, but to signal the readiness to escalate, if necessary, to strategic nuclear attack. This would make it clear to the adversary “that there was no point continuing and they had better desist” and, it was hoped, would de-escalate the situation and restore deterrence.
Any escalation strategy, however, has to be translatable into messy reality. Historian Beatrice Heuser points out that there is a longstanding assumption that when one side makes a move, the other side will correctly interpret the signal they’re being sent. But judging by Cold War precedent, this, she warns, is “very questionable”: a problem Kahn himself accepted. One issue, visible in the Soviet Union in the early 1980s, was that leaders can become convinced that everything the other side does, no matter how well-intended, is really a trick. Gorbachev’s great innovation, Heuser suggests, was to believe his opponents’ claims of peaceful intent; today, “Putin seems to be caught in that conspiracy bubble—everything we do is just a cover for harming Russia.”
And then there is another potentially fatal assumption: that your opponent thinks as you do. Kahn acknowledged this, too, presenting a hypothetical Soviet ladder of escalation, which looks worryingly different from his American version. As Tebbit says, “the flaw in the concept” is that “you had to assume that the other person had, broadly speaking, shared the same rationality you have. If that was not the case, then you were in trouble”. To forestall that, much effort was put into ensuring the other side “understood exactly what we thought their view would be”.
So perhaps Kahn’s approach is both useful and delusional. Or rather, useful, then delusional. Plotting out the first few “rungs” by which a given crisis might develop seems reasonable, but only while it stays this side of the nuclear red line. If that seven-decade taboo were shattered, the notion that escalation would proceed as the ladder lays out seems all but utopian. There would be too many variables; the stakes would be too high; there are no precedents. Drawing in part on his time at US Strategic Command, Post warns that “sometimes decision-makers think they may have more control” than they actually do—they think they can “predict the maximum level of violence that’s going to occur in a conflict”. Likewise, Scoblic warns that “the decision is going to be very little like what we think it’s going to look like”. Regardless of all those decades of strategising, a final crisis may come down to a handful of leaders making decisions under intolerable pressure, within a few minutes.
Yet some deterrence theory regards such uncertainty as a useful tool. In The Strategy of Conflict (1960), Kahn’s former Rand colleague Thomas Schelling argued for deploying what he called the “threat that leaves something to chance”: a way of turning the flaws and risks of leaders’ crisis decision-making—faulty communications, panic, false alarms—to strategic advantage. This involved the “deliberate creation of a recognisable risk of war, a risk that one does not completely control”.
Schelling’s chosen metaphor was not a ladder or a cliff edge, but “a curved slope that one can stand on with some risk of slipping, the slope gets steeper and the risk of slipping greater as one moves towards the chasm”. The point is that no one is sure how great the risk is, or “how much it increases when one takes a few more steps downward”. In this analogy, one is roped to one’s adversary; the trick is to put yourself in a position where you may fall. Rather than risk going down with you, the adversary may just back off.
Given the collapse in 2019 of the intermediate-range nuclear forces treaty, in place since 1987, experts in nuclear policy see gaps in the west’s deterrence that they think need plugging. Some in the US want to restore a programme for submarine-launched cruise missiles that was initiated under Trump in 2018 but cancelled under Biden. Others note that the US’s airborne nuclear deterrent still relies on ageing B52 bombers, produced only until 1962. And should Britain now replace the WE.177 air-dropped nuclear weapons, scrapped in 1998?
General Sir Richard Shirreff, who served as Nato’s deputy supreme allied commander from 2011 to 2014, argues that while conventional forces should also be bolstered, not restoring intermediate-range nuclear weapons means “you’re placing a greater dependence on what I think is not a credible option”: that is, the threat of using strategic nuclear weapons in response to a relatively contained crisis.
Beatrice Heuser is among those who contend that modern conventional missiles are now far more precise than during the Cold War, and could credibly play a greater role in deterrence, especially as using them would not involve violating the nuclear taboo. Critics warn, though, that advanced conventional strikes could be misread as doing just that.
And if Putin does decide to use a tactical nuclear weapon to stop Ukraine retaking Crimea? Scoblic argues the US and its allies would have a horribly difficult balance to strike, punishing the violation of the nuclear taboo without cornering him. As things stand in the war, Admiral Stavridis doubts Putin will use a nuclear weapon, but suggests that “Putin would not hesitate to use nuclear options if his regime or his own survival were threatened”. (In this light the Prigozhin rebellion is, he thinks, “very dangerous”.) Were Putin to use a nuclear weapon, the west would have to steer a path between “very dangerous escalation” and falling victim to “nuclear blackmail”. He suggests Nato would instantly respond, not with nuclear weapons, but against “massive conventional targets” such as the Black Sea Fleet, and:
probably military targets in Crimea and Kaliningrad. A no-fly zone would immediately be put in place over Ukraine. Russian forces in Ukraine would be attrited significantly by Nato air strikes. Hopefully that would deter Putin from further use of nuclear weapons, and cause him (finally) to back down. But he could choose to double down and use more nuclear weapons against a broader target set in Ukraine. It would be easy to see further escalation from both sides in that scenario.
His erstwhile deputy, Richard Shirreff, largely concurs, though he doubts Russia itself would be attacked.
Coming to this field as a non-expert, as a student of the workings of political fear, the thing that strikes me most about Kahn’s ladder is the manner of its creation. By stretching his scenario so far beyond the first use of nuclear weapons, he exposes the ambiguous, head-spinningly slippery but unavoidable role of the imagination in escalatory crises. The Cuban Missile Crisis came close to destroying much of humanity, a prospect seared into the minds of those closely involved. The fact that only one person was killed does not diminish that. In an escalatory crisis, what each side imagines is about to happen—and what it imagines its adversary imagines is about to happen—is central to finding a way to de-escalate. But if that fails and those weapons are used for real, what then happens next might look nothing like anyone’s imaginings. So controlling escalation means using the imagination to keep what both sides imagine imaginary.
Given all this, it’s not surprising that both Stavridis and Shirreff followed their roles commanding Nato forces in Europe by writing novels that sketch out near-future wars. It may be that China is restraining any nuclear use by Russia in Ukraine, but Stavridis’s novel of world war in 2034 presents a quite different escalatory scenario. It begins with a small naval clash between the United States and China. It ends with a mushroom cloud over Shanghai.