Deterrence — Sounds simple, not so straightforward in practice

Over the last 12 months or so, there has been considerable talk about deterrence, particularly in relation to how China might be deterred from taking military action against Taiwan. There is a general understanding of the nature of deterrence, i.e. the threatened use of force to convince an adversary “not to do something”. In practice, however, effective deterrence is complex, especially when the threat is based on conventional weapons and when the actor or actors posing the threat are not necessarily committed to carrying out that threat if deterrence fails.

Based on the desire to better understand the nature of conventional deterrence, some 25 years ago, I conducted a detailed study of conventional deterrence, comprising:

• the relevance of conventional deterrence;
• forms of deterrence; deterrence theory;
• empirical analysis – the historical record; and
• criticisms and limitations of conventional deterrence.

The full study is available here. From this detailed study a number of conclusions were drawn.

In the 25 years since the study was completed, three major developments in the strategic environment that potentially change the nature and application of conventional deterrence can be identified:

1. The importance of the information domain in warfare and the development of cyberwarfare.
2. The increased importance of space to military operations.
3. The rise of China as a major military power across all warfare domains, with nuclear weapons and advanced delivery systems and a challenger to the rules-based order established since the end of World War II led by the United States.

On re-reading the study, notwithstanding these major developments, the conclusions drawn from the original study remain valid and need to be taken into account in any assessment of the likely success of a deterrence strategy.  The conclusions, unchanged from the original study follow.

Conclusions

The [preceding] analysis shows that deterrence, while generally well-understood as a concept and widely applied in military and non-military contexts, is complex when considered in detail. The complexity is due to the interactive nature of any deterrence situation which involves a wide range of strategic, political, and psychological factors.

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This is particularly so for conventional deterrence and has led to a wide range of criticisms regarding its conceptual basis, theoretical understanding, and effectiveness in practice.

While not negating the value of conventional deterrence, these criticisms highlight its inherent contestability. This contestability is supported by the results of empirical analyses which, while providing conflicting results on the success of conventional deterrence, show that it can be effective in practice. Because it can be effective and because peace-loving nations will always prefer to deter conflict than to fight, conventional deterrence will remain a fundamental feature of security strategies.

But because conventional deterrence can fail, its weaknesses as well as its strengths must be recognised.

Specific conclusions which can be drawn from the preceding analysis are as follows:

1. Conventional weapons can provide a credible deterrent threat

Advanced conventional weapons allow decisive military action while limiting collateral damage and danger to one’s own forces, a major determinant of advanced nations’ involvement in any future conflict. The success of advanced conventional weapons in the Gulf War has led to high hopes for the future stabilising role of conventional deterrence.

2. Although credible, conventional deterrence is inherently contestable

Factors which contribute to the inherent contestability of conventional deterrence include:

• The costs of conventional warfare are far more bearable than for nuclear warfare.
• The outcome of any conventional conflict is difficult to predict in advance. A major factor in this unpredictability are “human factors” which are hard to quantify, difficult to communicate and difficult to prove except in combat.
• The outcome of future conventional conflict will be dependent on the application of advanced weapons, the capability of which may be difficult to communicate to a less technically advanced adversary.

3. Advanced conventional weapons are not a panacea

Although some see the Gulf War as a turning point in the nature of warfare, care should be taken in generalising from the results. Future crises will have their own unique characteristics and, as the conflict in Bosnia has shown, advanced conventional forces cannot take on all missions. Lessons have been learned from the limitations of advanced conventional weapons in Bosnia and the inability to locate, defeat and defend against Iraq’s Scud missiles.

4. Deterrence is not applicable in all circumstances

There is, however, nothing within deterrence theory to assist in determining where and when it should be used. These decisions must be based on political considerations that take into account a wide range of strategic issues.

5. Deterrence is only a strategy

Deterrence is a means to an end, not an end in itself — it is a tool at the service of policy.

6. Deterrence can be self-defeating leading to reduced stability

Because threats can provoke as well as restrain, they must be applied carefully. Capability must not be so great that an adversary sees itself as threatened. A major determinant in assessing the appropriate level of forces to provide effective deterrence will be the relative balance between offensive and defensive capabilities.

7. Deterrence does not provide a long-term solution

At best, deterrence is a stabilising mechanism — it cannot remove the source of tension in an adversarial relationship. It may, however, be essential in stabilising a situation such that diplomatic and political solutions can be found.

8. Rational deterrence theory, while based on a simplifying assumption of rationality, is still analytically useful

While the assumption of rationality on which rational deterrence theory is based has been widely criticised as too simplistic, empirical analyses have shown that aggressors will at least make an assessment of the likely success of military action before acting.

9. Communication, capability and credibility are factors necessary but not sufficient for deterrence success

Rational deterrence theory proposes that the success of a deterrent strategy is based on consideration of communication, capability and credibility. Analysis of past conflicts shows, however, that while these are necessary for effective deterrence, they are not sufficient.

10. The balance of interests is a major determinant of the success of deterrence

Empirical analysis has shown that the level of interest in the stake being challenged is a major determinant of deterrence success. It is where the level of interest, and hence commitment, is questioned (most likely in cases of extended deterrence) that credibility is most likely to be questioned.

11. Deterrence is psychological in nature and based on perceptions

In considering the likely success of deterrence, it must be recognised that:

• It is the adversary’s perception of the capability and credibility of a deterrent threat that determines its effectiveness.
• It is only where the aggressor is not committed to action and the deterrer is perceived to be committed to carrying out the threat that deterrence is possible.

12. Leaders may refrain from military action if a viable alternative option is available

Empirical analysis has shown there is a direct relationship between a narrowing of the bargaining range and the use of force. When adopting a deterrence strategy, therefore, it may be necessary to provide a “graceful” way out so that the aggressor does not lose face.

13. Conventional deterrence can be achieved through denial

Because defence against conventional weapons is possible, conventional deterrence can be achieved by denial. Denial does not necessarily mean there is no offensive capability. The aim of the offensive elements, however, would be to directly defeat the aggressor’s military capability rather than to raise the cost of aggression.

14. A strategy of pure defence may be more a myth than a reality

Whereas a strategy of defence is based on a consideration of capability only, deterrence by denial also takes into account consideration of communication and credibility. Once a defender seeks to reduce the likelihood of an attack by communicating capability and willingness to use force to defend its interests, the strategy has essentially become one of deterrence by denial.

Because defenders will always (even if implicitly) communicate their capability and intentions, a strategy of pure defence may be more a myth than a reality. The essential difference between deterrence by denial and defence is a temporal one, deterrence being a peacetime objective and defence a wartime value.

15. A strategy of deterrence by denial may not be sufficient to deter aggression

Where the balance of forces is such that it may not be possible to convince a potential adversary that aggression would not succeed, the addition of an ability to punish can raise the cost of aggression and increase the likely effectiveness of deterrence.

16. Conventional deterrence can fail

Because conventional deterrence is inherently contestable, failures are inevitable. Failure, however, does not automatically lead to conflict. Depending on the nature of the adversarial relationship there may be progression from basic to general to immediate deterrence, with opportunities to reinforce the credibility of the deterrent threat at each stage.

Even if conflict does occur it does not necessarily mean an all-out attack. Historically, nations have favoured limited probes to test a deterrer’s resolve. Decisive action will be required to reinforce the credibility of the deterrent threat, but the response must not be so “disproportionate” that undesired escalation occurs and allied or international support is lost.

17. The cost of inaction is a key determinant of the likely outcome of a deterrence situation

Because aggression can be motivated by need as well as opportunity, an assessment of costs as well as gains can be a major determinant of deterrence success. While rational deterrence theory essentially assumes that aggressors are motivated by “opportunity”’, “motivation based on need” must also be considered.

When aggressors are motivated based on need — either from internal or external pressures — action may be taken even in the presence of a credible military threat.

18. An ambiguous commitment will reduce the effectiveness of deterrence

While deterrence is based on creating uncertainty in the mind of the aggressor, uncertainty regarding commitment is likely to reduce the effectiveness of deterrence. Although an ambiguous commitment may provide some deterrent effect, explicit statement of intentions will be required to maximise effectiveness.

19. An understanding of strategic culture and strategic personality is required

Because different personalities and different cultures have different value systems and different ways of responding to threats, asking the question “How would I respond in this situation?” is not adequate for predicting deterrence success.

An understanding of strategic culture is required to allow these values to be understood, manipulated or targeted. This is equally important for strategies of deterrence, reassurance and positive inducements and for determining the appropriate mix of these strategies.

20. Highly motivated aggressors will view a range of options to challenge deterrence

To be effective overall, deterrence must be effective at all levels of conflict. A strongly motivated aggressor will explore a range of options to challenge successful deterrence at the conventional level.

21. Specific instances of conflict do not necessarily mean a general failure of deterrence

Redirection of acts of aggression to less serious ones can be seen as a sign of deterrence success rather than deterrence failure.

22. A long-term perspective is required in assessing the success of deterrence

To assess the overall effectiveness of deterrence in an adversarial or potentially adversarial relationship, a long-term perspective is required. Ironically, short-term failures of deterrence and decisive acts of compellence may be required to establish the credibility of a deterrent threat and, hence, long-term stability.

23. A mix of strategies will be required to maximise the likelihood of maintaining stability

To maximise the effectiveness of conventional deterrence, parallel strategies of reassurance and positive inducements must also be applied. The aim of the combination of stabilising mechanisms is to convince an adversary that:

• Aggression would not be profitable (deterrence).
• The deterrer has no aggressive intentions (reassurance).
• There are beneficial outcomes from cooperative activity (positive inducements).

24. Deterring conflict short of war is possible but is more likely to be inter-conflict in nature

Conflict short of war does not represent a fundamental threat to the survival of the nation but a decisive response will be required. Deterrence is therefore most likely to take the form of inter-conflict deterrence — a decisive response in one case will be required to display capability and resolve to deter other instances.

In this form, deterrence is more a police-type action — keeping undesirable activity down to an “acceptable” level. Where the aggressor is identifiable as a state actor, escalation of the conflict is possible to avoid inefficient use of one’s own forces. Undesirable escalation that could lead to widening of the conflict and loss of allied or international support must be avoided.

25. Conventional deterrence can be countered

A number of strategies can be adopted to counter successful deterrence at the conventional level. These strategies include:

• Controlling the threshold of conflict – the aim being to reduce the level of conflict below the threshold of involvement.
• Controlling of the spectrum of conflict – e.g. by acquisition of weapons of mass destruction (WMD) or adopting guerrilla/terrorist tactics.
• Strategies of exclusion – relevant in the case of extended or cooperative deterrence where the costs of intervention are raised by threats of terrorism and raising the costs involved (particularly in terms of casualties) so nations are “deterred” from participation.

These strategies for countering deterrence are most likely to be effective in the case of extended deterrence where commitment will be based on a political assessment of the interests at stake. Where a nation’s own interests are at stake, there will be little doubt that a deterrent threat will be carried out.

26. Deterrence can be applied in immediate, general and basic forms

While deterrence is generally considered in the form of immediate deterrence (where a specific threat exists), it can also be applied in the general (specific adversary, no specific threat) and basic forms (only potential adversaries). In cases of immediate deterrence, the potential aggressors are generally highly committed to challenge because significant political costs are associated with backing down.

The less committed to undesirable action a potential aggressor is, the more likely deterrence will be successful.

27. Proliferation of WMD and advanced delivery systems pose a serious threat to conventional deterrence

The self-deterrent effect of WMD experienced by major powers is unlikely to be present for rogue states seeking to acquire WMD to obtain leverage over otherwise more powerful states.

Unlike conventional forces which take considerable time and money to acquire and develop, they can be obtained relatively quickly and cheaply. They can therefore destroy the warning time and the inverse relationship between the likelihood and seriousness of threat created by successful conventional deterrence.

Because the damage caused by the use of even limited numbers of WMD would be unacceptable, action must be taken to prevent their proliferation rather than their use.

28. International deterrence will be of increasing importance

The success of coalition action in the Gulf War and increasing levels of international economic interdependence will lead to an increase in the importance of international deterrence. But the failure of international action in Somalia and the former Yugoslavia shows that international deterrence will not have credibility in all cases.

This is because, as for all forms of deterrence, credibility is based on an assessment of the interests at stake — decisive action will only be taken when it is clearly in the interest of the major powers. A key factor in the future success of international deterrence will be the UN’s willingness to support counter-proliferation action where proliferation of WMD occurs.

John Harvey is a retired Air Marshal in the Royal Australian Air Force (RAAF). His ADF career spanned more than 30 years, with early emphasis on employment as a Navigator and weapons officer in Canberra and on F111 aircraft and later in more diverse roles such as technical intelligence, military strategy, visiting fellow Strategic and Defence Studies Centre at the Australian National University, and program manager for the Joint Strike Fighter Project for Australia. He also served as NSW defence advocate from June 2016 to September 2021.