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Joint Air & Space Power Conference 2017

Deterrence in the 21st Century

By Dr Jeremy Stocker, Directing Staff of the Joint Services Command and Staff College (JSCSC), Shrivenham

Memorandum – Associate Fellow Royal United Services Institute

The Nature of Deterrence

SI VIS PACEM, PARA BELLUM – If you want peace, prepare for war. This ancient adage expresses an idea at the heart of the concept of deterrence. It is also a prime example of what the strategic writer Edward Luttwak calls the paradoxical nature of strategy, namely that much of strategic thought, theory and practice is counter-intuitive. Put simply, only arms can fight a war. Yet arms are also required to prevent war. This is because of deterrence.

Deterrence is especially ‘paradoxical’ which is why it is so often misunderstood or dismissed. It also, as Lawrence Freedman has observed, often performs better in practice than in theory despite, or perhaps because of, the complexity of much deterrence theory, a good deal of which is derived from the nuclear era. And if that was not complicated enough, it is also the case that deterrence can rarely be ‘proved’, in that when it is successful nothing happens. Why it didn’t happen often lies in the realm of counter-factual speculation and can rarely be quantified. What is clear, however, is when deterrence fails for then the unwanted outcome does occur.

Deterrence seeks to dissuade one party from undertaking actions that another party deems unacceptable. By removing a cause for war deterrence is therefore a powerful tool of conflict prevention, as well as a means of limiting the scope and nature of existing conflict. It can also serve to reinforce existing norms of behaviour, for example against the use of chemical weapons, by holding out the prospect of baleful consequences if such norms are broken. Deterrence, fundamentally, is about containment – containing potential adversaries and containing security problems.

Since the advent of nuclear weapons, deterrence has most commonly been associated with threats of retaliation – deterrence by punishment in the jargon. This is because of the impossibly high standards required of a worthwhile defence in the face of threats that are nuclear, numerous and sophisticated. During the Cold War nuclear stand-off even a 95 % effective defence, if such could be devised, was of little point as 5 % of a lot was still a lot. But a promise of retaliation is not the only deterrence mechanism. Deterrence by denial offers the prospect of successful resistance to unwanted acts, to defeat them on their own terms and therefore remove the incentive to undertake them in the first place. Both forms of deterrence pre-date the nuclear age, are not mutually exclusive and have continuing relevance. A comprehensive deterrence posture will combine both, promising both to defeat aggression and to offer the prospect of subsequent consequences. Those consequences need not necessarily be military.

The Functioning of Deterrence

Deterrence is a relationship between the deterrer and the deteree. Like all relationships, it is critically reliant on effective communication. The deterrer must make clear what it is that is to be avoided and the likely consequences if it is not. The deteree has to understand and act upon that message. Communication may include, but need not comprise, direct conversation. Signalling and perceptions are as important as first-hand communication. As such, deterrence is a deeply human, subjective activity subject to the psychology of perceptions, values, determination, assumptions, motivations and decision-making. As Keith Payne puts it, deterrence is an ‘uncertain art, not a precise science’.

A deterrence posture can be both general and specific. General deterrence is an expression of a state’s reputation and capability. A former MoD Chief Scientific Advisor, Sir Hermann Bondi, once observed that a nuclear-armed state is one that no one can afford to make desperate. That is general deterrence. The strategic maxim ‘don’t invade Russia’ pre-dates the nuclear age and is another expression of general deterrence, as Russia (with or without nuclear weapons) is a state not to be messed with.

Specific or immediate deterrence is scenario-dependent. It relates to a particular actor and a particular act that one wishes to deter – for example, Syrian use of chemical weapons or an Argentine invasion of the Falkland Islands. The promised response, whether of the punishment and/or denial variety, needs to be tailored to the specific circumstances and communicated accordingly. This can suggest ‘red lines’ not to be crossed, but explicit and precise red lines can be counter-productive. They can suggest a range of undesirable actions which, because they stop short of the line, could be perceived as tolerable. And if the red line is crossed a response is required if deterrent threats are not to become incredible even if, under the circumstances, the deteree might not wish, or might not be able, to respond as previously promised. The recent crisis over the use of chemical weapons in Syria is a case in point. ‘Studied ambiguity’, a hallmark of the UK’s nuclear deterrence posture, has much to commend it. Equally, however, the deteree must understand the threat proffered and the action to be avoided. This is a delicate and ever-shifting balance.

Deterrence is critically about credibility. The threats and promises on which deterrence is based must be believable and believed. This is a function of capability, will and communication, as understood by the deteree, for it is the other party who decides whether or not to be deterred. Proportionality is key as disproportionate threats may be not just illegal but also unbelievable. And it is important not to over-threaten as doing so will generate the very hostility that deterrence is meant to counter.

A critical problem is self-deterrence. Why would you want to deter yourself? You don’t, but that can be the effect of a myriad of factors not least issues of proportionality, respective values, legal constraints and the extent of vital interests at stake. In the 1990s the Serbian leader Slobodan Milošević is reputed to have said ‘I am prepared to walk on bodies, but the West is not. That is why I shall win.’ He was wrong about winning, but right to speculate that the Western powers could be self-deterred, in that they had less at stake and were not prepared to undertake certain actions – indeed, arguably they showed a greater concern for Serbia’s civilian population than did the Serbian leader himself. The same observation could be made about Saddam Hussein or Muammar Gaddafi.

Much of the problem of self-deterrence arises because of asymmetries of interest. Where one state has vital interests at stake, perhaps regime survival, but the other does not there will also be an asymmetry of will and purpose. Deterring actions that are objectionable but stop short of threatening national survival needs to be more nuanced than when the stakes are higher. And a perception that you will be self-deterred, whether accurate or not, will itself undermine deterrence and the deteree be tempted to call your bluff. International crises are made of these sorts of misperceptions and miscalculations.

Deterrence is often, though not always, a two-way relationship. Others may seek to deter us as we seek to deter them. The Cold War nuclear rivalry was an obvious and relatively simple example of this mutuality. More often, while two parties do seek to deter each other, they try to deter different things, for different reasons and in different ways. For example, The United States wants to deter Iran from developing nuclear weapons, attacking Israel or threatening its Gulf Arab allies. Iran wants to deter the US from intervening in the region. Each seeks to limit the other’s freedom of action whilst preserving its own.

Because being deterred limits one’s freedom of action no state will willing acquiesce in its own deterrence, except perhaps in the important instance of mutual nuclear deterrence between ‘peer competitors’. So ‘counter-deterrence’ is an important requirement for both strategy formulation and force planning. For example, Western powers have little option but to be deterred by the Russian nuclear arsenal when vital interests collide. They will not want to be similarly deterred by the embryonic nuclear capabilities of North Korea or Iran. So a mix of non-proliferation measures and active defences is used to prevent or retard these capabilities and to negate them if they are nonetheless acquired.

The prevention of conflict and the deterrence of threats to national interests are the essential tasks of military forces. In the UK of late, however, this has tended to be obscured by the country being strategically ‘fixed’ by operations in Iraq, Afghanistan and elsewhere such as the Persian Gulf, the Horn of Africa and the South Atlantic. National strategy and force planning have been focussed on the ‘here and now’ commitments leaving little capacity for contingency and wider deterrence. And deterrence requires the demonstration of available and responsive capability. Armed intervention does just that, but once intervention becomes semi-permanent the opposite holds true as enduring commitments reduce responsiveness and flexibility. The UK’s post-Afghanistan ‘return to contingency’ restores a degree of responsiveness that is the necessary underpinning of deterrence and conflict prevention. Their forward but non-territorial presence makes maritime forces of especial utility in this regard.

Nuclear Deterrence

Deterrence is about a good deal more than just nuclear deterrence, but the latter retains a central place in the theory and practice of deterrence. It might be noted in passing that nuclear deterrence can be the deterrence of nuclear threats or the use of nuclear weapons for deterrent effect. Intimately linked though they are, they are not synonymous. Nuclear use can, conceptually, be deterred by other means rather than, or in conjunction with, threats of nuclear retaliation. And nuclear threats can deter more than just other nuclear weapons. The presence of nuclear weapons certainly exercises a cautionary effect all round and their general war-prevention role has long been a central pillar of NATO’s nuclear doctrine. It is, critically, nuclear weapons that have made major war between the Great Powers virtually unthinkable. Nuclear abolition, were it ever to be possible, might not be an unmitigated good.

It is sometimes asserted that nuclear weapons are purely ‘political’ and that they could never be used. This is a substantial fallacy in two senses. First, as the late Sir Michael Quinlan pointed out, ‘Weapons deter by the possibility of their use, and by no other route.’ An ‘unusable’ weapon, nuclear or not, will deter no one. That is why, however remote the possibility of their use, it is necessary for nuclear states to have doctrines and plans for their employment. To rely solely on the existential awfulness of nuclear weapons is insufficient as the party most likely to be thus deterred is oneself. Second, nuclear weapons are actually ‘used’ everyday in performing their core deterrent function.

Two observations about Continuous-at-Sea Deterrence (CASD) may be appropriate here. First, because deterrence is all about signalling and credibility abandonment of CASD would send a powerful signal that while the UK is not ready to abandon nuclear weapons it is not really serious about threatening their use – remembering that it is others’ perceptions, not ours, that ultimately matter. And second, maintenance of CASD provides an assured retaliatory capability in times of crisis, which is when its possession becomes important. In the absence of CASD in order to establish a credible deterrence posture it is necessary to receive and correctly interpret indicators and warnings of a deteriorating situation, and then to take the necessary political decision to deploy in time (assuming that time is available). This necessarily sends an escalatory signal at just the time when the government of the day might be seeking to do the opposite and de-escalate the situation. The relatively modest financial savings to be had from abandoning CASD make the serious compromise of the UK’s deterrent posture and capability a very poor bargain.

Non-Deterrable Actors

A frequent criticism of deterrence is that some threats are non-deterrable. An irrational actor, it is asserted, cannot be deterred. However, instances of genuinely irrational (‘mad’) actors are thankfully rare. It is rather that not all rationalities are the same. It all depends on an individual’s, a group’s or a state’s underlying assumptions, perceptions, beliefs and values. A deterrence posture directed at a potential adversary must reflect these. It is essential to understand others’ values and motivations and not simply assume mirror-images of our own. The concept of ‘tailored deterrence’ is emerging in the United States to take account of these differences. And even this only applies to retaliatory deterrence. An ability to counter potential threats (defeat them) is just as important a deterrence tool. It establishes a degree of physical control lacking when one relies solely on a threat of retailiation.

Non-state actors are a related difficulty. In the event of anonymous attack by terrorist means, against whom should one retaliate? In this instance effective defence is critical to neutralize or deter the threat. But few threats are genuinely non-state and non-territorial. State-sponsorship or at the very least state acquiescence in non-state action makes accountability more difficult to establish, but not impossible. The relationships between Al Qaeda and the Taliban in 2001 or between Hezbollah and Iran today are cases in point.

Ballistic Missile Defence

The role of Ballistic Missile Defence (BMD)1 has become both prominent and controversial. The Cold War has unfortunately left a legacy of doctrines and assumptions that no longer fully hold true. It remains the case that, as observed earlier, that in the face of substantial nuclear arsenals (Russian and, increasingly, Chinese), BMD has little to offer and nor can it undermine the ability of a serious nuclear power to devastate whomsoever it might choose. In the case of small, emergent nuclear powers, however, BMD holds great promise. The ballistic delivery capabilities of recent and emergent nuclear states like North Korea, Pakistan and Iran are, though effective, based on very old rocket technology and are limited in numbers. And all actual use of ballistic missiles has, to date, involved non-nuclear payloads. Modern BMD systems, especially in the areas of sensing, computing and discrimination, offer the prospect of effective and worthwhile defence against threats that are modest in both numbers and sophistication. This is, crucially, a deterrence function as the ability to counter a missile strike reduces the utility and attraction of undertaking, or threatening, an attack in the first place.

There is also an important non-proliferation aspect to BMD. Missile defences substantially raise the bar, technological and financial, of effective nuclear/ballistic ‘entry’, while by denying ballistic missiles a ‘free-ride’ it reduces their attractiveness for strategic leverage.

Following NATO’s 2010 Lisbon summit, the Alliance has placed BMD at the heart of its core Article 5 mission. But NATO has yet to address the looming problem of nuclear burden-sharing as the highly symbolic Dual-Capable Aircraft (DCA) approach the ends of their lives. A new generation of DCA looks highly unlikely on political and financial grounds. Done cleverly, BMD could provide an alternative means of burden-sharing in the nuclear arena, adopting a Denial rather than a Punishment deterrent mechanism.


Deterrence remains of fundamental importance in states’ external security relations. It is also the basic purpose of a country’s armed forces. Deterrence, when successful, prevents security problems arising or contains them when they cannot be prevented. There is an essential nuclear dimension to deterrence but it is not a purely nuclear matter. As the UK returns to ‘contingency’ deterrence needs to be at the heart of strategy formulation and force planning in order to optimize its contribution to the defence of the UK’s vital interests.

1. For a fuller discussion of the role of missile defences, see the author’s ‘The Strategy of Missile Defence: Defence, Deterrence and Diplomacy’, RUSI Journal Jun./Jul. 2011.

Dr Jeremy Stocker serves on the Directing Staff of the Joint Services Command and Staff College (JSCSC), Shrivenham. He has also advised all three UK main political parties on the subjects of missile defence and nuclear deterrence, and given evidence to the House of Commons Defence Committee.