Military strategy is the art of deciding how to use armed force to achieve strategic objectives. It is not one of Australia’s strengths. The federal government spends tens of billions annually on submarines, major warships and fighter aircraft that are only useful in major wars, and it pays little attention to how it would use them in a conflict.

That’s hardly surprising, because for most of Australia’s history the government has left military strategy to its major allies. And over the long decades since Vietnam, few Australians have taken the possibility of major war seriously – not even those making the big decisions in Canberra.

But that has changed. Last week the Morrison government released the 2020 Defence Strategic Update and at last acknowledged how much Australia’s strategic environment has deteriorated and how fast the risk of major war is increasing. Now it must think carefully about what Australia’s armed forces are actually supposed to do if the country faces a serious military threat.

The government’s starting point should be its military strategy. That strategy remains unstated, but it can be inferred from the armed forces Australia has now and those it is planning to build. It is a muddled amalgam of two largely incompatible ideas. The first is a strategy of maritime denial, which seeks to defend against an adversary by denying them passage through the country’s airspace and territorial waters. The second is a strategy of coalition, under which Australian armed forces contribute to a wider international effort further from its shores. Alas, these two strategies tend to pull our priorities in different directions.

Maritime denial was first set out in detail in the 1987 Defence White Paper and it remained the guiding idea behind Australia’s defence policy until the turn of the century. Many capabilities of the Australian Defence Force (ADF) are oriented towards it today.

The coalition strategy was Australia’s default position until the 1970s and it has recently been revived in response to the War on Terror and the growing power of China. The clear but unexpressed rationale behind some of Australia’s recent major investments is an assumption that, at some point, the ADF’s primary role will be to join a US-led coalition in a war with China.

The government’s new defence review introduces a third option: a strategy of deterrence. It says the old strategies are too defensive and proposes a more aggressive approach to deter hostile action before it is launched.

The defence review states that Australia’s armed forces “must be able to hold potential adversaries’ forces and infrastructure at risk from a greater distance, and therefore influence their calculus of costs involved in threatening Australian interests”. It also emphasises the importance of Australia taking “greater responsibility” for its own security and “grow[ing] its self-reliant ability to deliver deterrent effects”. This is notable in that the review otherwise abandons the concept of self-reliance that has been central to defence policy since the 1970s.

The argument for a strategy of deterrence has been made by the Australian government before. It justified Australia’s acquisition of its now-retired F-111 long-range bomber force, for example. But it has never been given the central role suggested by the new defence review. It is therefore worth asking whether it is likely to work and to work better than the alternatives.

Deterrence is always an alluring idea, because it offers the prospect of winning without fighting. But like many alluring ideas, deterrence turns out to be more complex than it first appears. These complexities must be understood before deterrence can become Australia’s core military strategy. This is especially true when it is crystal clear that the adversary it aims to deter is China.

Deterrence can work in two ways. The first is to convince an adversary that any military operations it contemplates could not succeed due to the strength of opposing forces. Strategic theorists call this “deterrence by denial”. The second way, called “deterrence by punishment”, is to convince an adversary that any aggression on its part would be met by retaliatory action severe enough to outweigh any benefits it hoped to achieve.

These different versions of deterrence require different kinds of armed forces. To deter by denial, Australia would need forces that convincingly signal it is powerful enough to defeat any attack. To deter by punishment, Australia would need forces that signal its ability to inflict an unacceptable level of retaliatory damage on the homeland of its adversary.

Consider, for example, how China might be deterred from launching an attack on Papua New Guinea. To deter by denial, Australia would need forces that could prevent that attack from succeeding by inflicting damage on approaching Chinese forces. To deter the same attack by punishment, it would need forces that could inflict damage on China itself, as an act of retaliation.

While for decades Australia’s armed forces were designed to use the deterrence by denial strategy to some degree, it is clear that what the government now has in mind is deterrence by punishment. This is affirmed by the review’s repeated reference to the necessity of holding an adversary’s “infrastructure” at risk, and by its commitment to purchasing “longer-range strike weapons”.

Here, then, is the sixty-four-dollar question. How realistic is it for Australia to rely on deterrence by punishment to protect its interests and territory from China over the decades to come?

There are two reasons to doubt it being realistic at all. The first has to do with capability. To make its vision of deterrence work, the government would have to build armed forces that could threaten to inflict so much damage on China that Beijing would abandon important elements of its ambition for regional primacy. To inflict that kind of damage independently, as the review proposes, would not be easy. If nuclear weapons are off the table, as the review says they are, scores of conventional warheads would need to be placed on Chinese targets to even get their attention. And it would take hundreds to make any real impact. If submarines were used to launch those warheads on cruise missiles, dozens of submarines would be required to mount such an attack. This would be a truly massive investment.

The second reason to doubt the viability of the government’s deterrence strategy is the ability of its adversaries to play the same game. Deterrence by punishment won’t work if Australian threats of retaliation are met with intimidating counter-threats. And that, of course, is exactly what Australia could expect from China. China’s capacity to inflict damage is greater than Australia’s, and if it were confident that Australia’s threats were mere bluff it would ignore them.

The reality is that the only kind of deterrence Australia can credibly achieve is by denial. The armed forces best suited to this strategy are the ones that can win in battle. To defend its most important interests, Australia should concentrate on building these forces as cost-effectively as possible.

For Australia, that means a military strategy of maritime denial: using armed forces to deny hostile approaches from a major power like China by air or sea. An effective maritime denial posture will deter adversaries by making it clear that the costs and risks of military action against Australia or its most vital interests will be prohibitive. I argue in my book How to Defend Australia that this is achievable, but it will require a more serious and disciplined approach to military strategy than anything detailed in the new defence review. And it will mean dropping the fantasy that deterrence by punishment offers any shortcuts to security in the decades ahead.