Nuclear Deterrence Reconsidered: The Emerging Threat of Limited Nuclear Warfare

Introduction

According to Clausewitz, war is ‘the continuation of politics by other means’,[1] and the use of military force is therefore guided by political objectives. A limited war, consequently, can be described as a conflict in which belligerents do not harness all available military resources and in which the utter destruction of the enemy is not the objective; it is confined with regard to the intensity of fighting, geography, and political aims.[2] There can be other things at stake, such as territory and power, and the sacrifices made must be proportional to the value of the political goals.[3] When one side decides that defeat in a limited war is preferable to escalation into total war and its consequences, the war comes to an end.[4]

Regarding limited nuclear war (LNW), a conflict involving the controlled and restricted use of nuclear weapons, there is no universally accepted definition. To some, including American strategist Bernard Brodie, the very notion of a ‘limited’ nuclear war is conceptually implausible. The destructive power and escalation risk of nuclear weapons, it is argued, make true limitation nearly impossible in practice.[5] For the sake of clarity, and in line with the concept of limited war, this paper proposes that an LNW would involve low-yield nuclear weapons (LYNWs), a limited number of warheads, for limited military and political objectives, and confined to a relatively small geographical space.[6] While an empirical answer to the question of LNW’s feasibility cannot be established, this paper argues that the likelihood of states adopting an LNW strategy is increasing. Due to shifting global power dynamics and technological advancements, the use of nuclear weapons could, if specific conditions are met, achieve political objectives without the conflict escalating into all-out nuclear war in a way that Cold War dynamics did not. However, attempting to do so involves treading a fine line, and the risk of escalation remains substantial.

The Dilemma

The main problem with the concept of LNW is that, in the fog of war, it is difficult to convey to the enemy whether a first strike is truly limited or the initial step in an all-out nuclear war. Between the 1960s and 1980s, RAND Corporation and the Pentagon conducted multiple wargames that tested various LNW scenarios as an alternative strategy to Mutually Assured Destruction (MAD), since the latter left little room for gradual escalation control and was therefore seen as a flawed deterrent vis-à-vis the Soviets. However, as most of these scenarios escalated into total nuclear war, the theory of LNW partially receded into the background, despite several U.S. presidents occasionally considering flexible nuclear options.[7] It was followed by an approach to limited war that was fought with conventional weapons.[8]

In recent years, a limited nuclear strategy has been receiving renewed attention. The geopolitical landscape has changed drastically since the end of the bipolar order of the Cold War, which has implications for nuclear strategy as well. In a more complex world that is moving towards multipolarity, with the USA increasingly losing its dominant influence, and with different forms of governance possessing a nuclear arsenal, the international landscape is changing. The old theories of deterrence and escalation might therefore not function as they used to.

Nuclear Strategy and the Modern Nuclear Landscape

The feasibility of LNW rests on several assumptions and criteria that all have to be met:

1. A state can achieve strategic goals with nuclear weapons that it cannot realize with conventional ones, such as the destruction of certain infrastructure or intimidating the enemy.
2. The first user requires a spectrum of nuclear capabilities, ranging from LYNWs to high-yield nuclear weapons (HYNWs). HYNWs need to be held in reserve as a deterrent, so that the employment of LYNWs will not automatically lead to large-scale escalation, such as the destruction of densely populated civilian centers.[9] If the target is a non-nuclear state, such a one-sided nuclear exchange is unlikely to escalate as long as it is not backed by one. If the target is a nuclear state or falls under the nuclear umbrella of one, escalation might ensue. Later sections will discuss the determining factors in this equation.
3. An attack must convince the opponent of its limited scope while simultaneously instilling enough fear to alter its behavior. Fred Kaplan, author on nuclear strategy, calls this paradox the ‘unresolvable dilemma’.[10] This is where historical war games often escalated, such as the Proud Prophet war game of 1983, during which the USA attempted to escalate in order to de-escalate by deploying a LYNW to halt advancing Soviet forces in Europe. This resulted in massive retaliation by the USSR.[11]

The concept of gradual escalation only works if both enemies act according to the same playbook: a limited strike might be carried out perfectly, but the enemy must follow the same logic and escalation patterns as calculated by the first user, or be more risk-averse than the initial user.[12] Whether deterrence works depends on the other party’s strategic culture, mental framework, and acceptance of being deterred.[13] The mere use of a nuclear weapon might already be interpreted as taking off the gloves of limited war, thereby signaling the start of an escalatory spiral, since it is easier to determine whether the nuclear threshold has been crossed than to find out the underlying intentions of a nuclear detonation. ‘It takes two to keep a war limited’,[14] as stated by Lawrence Freedman, and once the nuclear red line has been crossed, it might become harder to signal to an enemy that limited objectives are still in place.[15]

Figure 1: Core criteria for the theoretical feasibility of LNW
Source: Created by and property of the author

Even if there is a slight chance that a limited nuclear attack could degenerate into a nuclear apocalypse, this might be enough to deter most rational actors from using even a LYNW first. Therefore, for LNW to be viable, it must be exercised with restraint and rely on a rational adversary, one who accurately perceives the intent to limit escalation and who is equally, or more, invested in preserving said limitation.

The Future Nuclear Actor

Who, then, might benefit from employing an atomic bomb first? At present, the USA is still the superior conventional military power. It has little to gain by starting a nuclear war itself, since these weapons can negate conventional superiority. Using them would upset the international order, weaken the nuclear taboo, and thereby undermine America’s might. Conversely, nuclear devices are the ‘ultimate instruments of stalemate… the ultimate weapons of the weak’.[16] Few are needed and they are easy to hide: the perfect safety guarantee for modern dictators, for whom staying in power often holds primacy over the security of their countries.[17] Having seen what happened in Libya and Iraq, autocratic leaders know that defeat could mean regime change. Losing must, therefore, be avoided at all costs. Research has indeed shown that leaders who manage a stalemate in war are twice as likely to stay in power and four times less likely to be punished.[18] During a conflict, they might rely on a strategy that involves a first-strike nuclear attack to timely force an enemy to disengage.[19] The more detrimental a defeat would be for their rule, the larger their incentive for such a nuclear escalate to de-escalate strategy. Initiating a nuclear conflict might benefit such actors in several ways:

• If there is a suitable target, an atomic device might produce a breakthrough on the battlefield or on critical infrastructure that conventional weapons could not achieve. It could, for example, destroy an enemy port, air base, or a fortified underground position. This radical improvement in military position could translate into strategic effects and satisfy criterion 1.[20] As per criterion 2, the first user must hold strategic reserves.
• It signals that they are willing to escalate and might thereby scare the enemy into relinquishing their objective. This usage could be worthwhile when facing a conventional military defeat or an enemy with superior conventional capabilities.[21]

The probability that starting an intended LNW leads to an advantage must trump the risk of escalation that is associated with atomic deployment.[22] In the ideal scenario, the shock triggered by crossing the nuclear threshold and the strategic gains that it creates on the battlefield are maximized, while the risk of escalation and retaliation from the other side is minimized.[23] If enemy retaliation neutralizes tactical gains, or if the enemy decides to escalate vertically instead of backing off, the nuclear option becomes less attractive. According to American strategist Herman Kahn, this limited game of chicken is a dangerous strategy.[24] As discussed, during the Cold War, it was concluded that the chance of escalation was too great to seriously consider a limited nuclear strategy. If these odds can be improved and criterion 3 (a nuclear attack must signal restraint while instilling enough fear to compel behavioral change) is met, however, LNW could become a viable strategy.

Managing Escalation

Shifting from the conventional to the nuclear domain is widely seen as vertical escalation in itself. Logically speaking, however, nuclear weapons do not have to be inherently incompatible with limited war. There exists a wide range in their destructive potential, and thereby their escalatory power, and the difference between LYNWs and HYNWs can be significant. In some instances, the difference in yield between LYNWs and HYNWs is greater than that between LYNWs and large conventional explosives.[25] Depending on the cutoff points used, LYNWs have yields between approximately 0.1 and 20 kilotons (kt), while HYNWs range from 100 kt to several megatons (Mt). For comparison, the Massive Ordnance Air Blast (MOAB), the largest conventional explosive, first used in combat on April 13, 2017, in Afghanistan, has a yield of about 0.011 kilotons.[26]

Figure 2: Explosive yield comparison of MOAB, LYNW, and HYNW (log scale)
Source: Created by and property of the author

Apart from the nuclear taboo, it can therefore be argued that the effect of a nuclear explosion in terms of its destruction determines an adversary’s reaction more than the size of the yield itself.[27] By controlling this outcome, a state can signal that an impending nuclear strike is meant to be limited. One method to achieve this is by adhering to the 1996 International Court of Justice’s (ICJ) stipulations on the use of nuclear weapons in the context of International Humanitarian Law (IHL) as much as possible.[28] Such a nuclear strike would:

1. Discriminate between combatants and civilians to the utmost;
2. Make sure the collateral damage is proportional to the advantage gained.
3. Be militarily necessary to achieve the military goal and cannot be attained through a less violent way;
4. Limit unnecessary suffering.[29]

Although not part of the ICJ’s provisions, limiting the duration of the conflict minimizes the chance of escalation as well.[30] All of the aforementioned conditions may be addressed through the use of so-called ‘clean’ nuclear weapons, devices with a higher energy yield from the fusion part of the nuclear reaction. This limits radioactive waste, thereby making the attack more discriminate and proportional, while causing less collateral damage and suffering.[31] Due to technological advancements in intelligence gathering, delivery systems, and nuclear weapons themselves, it is nowadays more manageable to meet the preconditions for a successful limited nuclear first strike than in the past.[32] If a clean bomb is used exclusively on military targets, or detonated in the upper atmosphere to disable the enemy’s electronic infrastructure (a nuclear-powered electromagnetic pulse (EMP) attack, which is nonlethal), for example, the terror effect of a nuclear weapon could be reached without evoking the same condemnation that is associated with the classical view of a Hiroshima-style destruction and without (massive) nuclear retaliation.[33]

Figure 3: Factors reducing nuclear escalation risk
Source: Created by and property of the author

Future Scenarios

In the current nuclear landscape, Russia would theoretically be well-situated to initiate an LNW, namely due to the autocratic nature of its government, the diversity of its nuclear arsenal, and its methods to manage escalation. While agreeing that global nuclear war would lead to MAD, nuclear weapons could have a more limited function in Russian doctrine instead.[34] In 2016, the RAND Corporation estimated that Russia could capture any of the Baltic capitals within 60 hours.[35] In such a typical ‘jab and grab’ scenario, Russia would have several limited nuclear options at its disposal that could indicate a willingness to adhere to the Law of Armed Conflict as much as possible. For instance, it could launch a clean LYNW on a US power-projecting base, such as an airfield, or decide on an EMP attack.[36] Taking these avenues would demonstrate an escalate to de-escalate strategy, and it is not certain that this would trigger a nuclear response.[37] In the case that one’s opponents have no practical options to retaliate in a similar ‘tit for tat’ fashion to a limited nuclear first strike, the initiator will have the advantage.[38] Illustratively, the number of nonstrategic US nuclear weapons, described by the Congressional Research Service as devices with relatively low yields and short ranges, decreased by 90% between 1991 and 2009.[39] This reduction hampers the US’s ability to escalate in a way that does not immediately involve HYNWs.[40] It might vacillate in using them because vertical escalation could be seen as disproportionate to the current situation.[41] Being confronted with a fait accompli, the USA and the rest of NATO might decide against nuclear reprisals, or even against full mobilization, since they do not consider the stakes high enough to risk full nuclear war.[42] Although NATO members are bound by Article 5 of the North Atlantic Treaty, and although the Baltics fall under the nuclear umbrella of the USA, intra-NATO nuclear policies differ substantially.[43] With the USA taking a progressively isolationist stance in the world, thereby indicating that it is increasingly less invested in defending other states, it cannot be assured that the traditional deterrence by punishment strategy would hold. During the Cold War, the USA had but one existential threat. Now, the country has many limited stakes in different regions. According to the Russians, crossing the nuclear threshold at a regional level might not jeopardize the core interests of the United States, and there is evidence to support this conclusion. During the Obama administration, Tony Blinken, then National Security Advisor to Vice President Joe Biden, already articulated to the National Security Council that the USA might not respond with a nuclear weapon of its own if Russia dropped a tactical nuclear weapon (TNW), which is generally a LYNW that is used on the battlefield or for limited military objectives, on NATO troops. Instead, he opted for economic isolation and conventional retaliation.[44] When facing an opponent that is conventionally superior, yet less invested, and more averse to escalation, starting an LNW might be worth the risk.

The example of Russia is but one, and some scenarios would not involve them or the USA. Henry Kissinger already argued that with smaller nuclear powers, deterrence might not function the same as during the Cold War dynamics, since they ‘have less to lose’ and since their ‘negotiating position might even be improved by a threat to commit suicide’.[45] Future nuclear conflicts are therefore thought to largely be regional.[46] Perceptions of rationality, moreover, differ across actors, cultures, and strategic paradigms, and are perpetually shaped by diverse other contextual factors. Different interpretations of the nuclear taboo can create asymmetries in the willingness to use nuclear weapons: modern conflicts can be regional and limited for one side, yet existential for one’s opponents.[47] When losing a conventional war, a state such as North Korea could wield a LYNW to break the nuclear taboo, thereby forcing a status quo ante bellum instead of having to cede territory or change its regime.[48] When a dictator is backed into a corner and has nothing to lose, given the asymmetry in escalation willingness, his opponents would be very careful in formulating a nuclear response themselves.[49] Coercion or deterrence through a limited nuclear strike might thus achieve strategic goals without leading to nuclear escalation.

Conclusion

Since their conception, only two nuclear weapons have been used in combat. Their destructive power is unparalleled, and friend and foe alike agree that MAD must be avoided at all costs. Against this backdrop, it is disputed whether LNW is possible and, if so, under which conditions and following which rules. This paper set out to argue that LNW is at present more likely than during the Cold War, due to technological developments and due to the changing nature of the geopolitical order. There are certain steps a state can follow to indicate that a nuclear strike is supposed to be limited and thereby lower the chance of vertical escalation. However, it should be emphasized that these arguments cannot be empirically verified and are difficult to encapsulate in war games. Following the rules of the Law of Armed Conflict as much as possible helps clarify intentions, but it provides no guarantees. Moreover, pursuing an LNW strategy inherently lowers the threshold for nuclear use, thereby increasing the likelihood of future nuclear escalation, even if the initial instance remains limited. Due to the lack of empirical evidence and the psychological nature of deterrence, the strongest conclusion that can currently be drawn is that LNW could be successfully employed by, for example, autocratic states that lack conventional military strength, or by actors confronting a more risk-averse adversary in terms of nuclear escalation, and that it is more likely now than in the past that this will happen.