If our strategic position was already challenging, it just got worse.

Reliability of the US as an ally is in question, amid such actions by the Trump administration as calling for annexation of Canada, threating to disband or leave NATO, and suddenly suspending support for Ukraine. This follows the 2023 Defence Strategic Review, which declared Australia’s strategic circumstances the worst since World War II.

As Australia seeks to urgently enhance its defence capabilities and sovereign capacity—including by acquiring nuclear submarines, long-range strike options, war stocks and emerging and disruptive technologies—our key ally of more than 70 years has become highly unpredictable.

In Australia’s immediate region, three critical questions arise. Can Australia depend on US military support, particularly the delivery of nuclear submarines within the AUKUS agreement?  Will the United States continue to develop and honour security agreements with Japan? And will the US help Taiwan in the face of potential Chinese aggression? This is not a complete list of concerns for the Australian government and Defence officials.

We should be careful not to throw our most fundamental alliance out with the bathwater of one US administration. But we had better start thinking now about what we would have to do if we needed greater defence self-reliance. To some extent, that implies preparations now.

As the old joke goes, if Australia asked for directions to a self-sufficient defence policy, the reply would be, ‘Well, you wouldn’t want to be starting from here.’  But here we are.

Despite early speculation, it is unclear how isolationist this Trump government will be. Its responses to Ukraine and Gaza present contrary pictures. It is important to remember that the US was isolationist and leaned heavily towards non-interventionism after the beginning of both World Wars I and II. Ultimately, it entered both conflicts on the same side as Australia. The bonds formed between Australian and American military forces in those conflicts are deep and enduring and are often invoked by politicians and service personnel alike. The dominant feature of the Australian defence headquarters in Canberra is a towering, stylised eagle symbolising Australia’s gratitude for US help during the Pacific war and the more than 100,000 Americans who died fighting there. America has been hard to predict and slow to react at times, but it has turned up for the free world when it matters most.

Despite some unnerving pronouncements from Trump, over the longer term the US has been more predictable and positive to Australia’s global interests. Australia benefits from American influence, even unpredictable American influence, as it helps maintain the mutually beneficial status quo. Beyond military advantages, our US alliance delivers essential intelligence through the Five Eyes intelligence partnership. The scale and breadth of that partnership would be nearly impossible to replace fully in any new arrangement.

I don’t like to imagine an Australian Defence posture without the US alliance, but I understand the need to consider the possibility. Australia would face an increasingly volatile world without the US as a strategic ally. It is wishful thinking to assume that Russia, China, North Korea or Iran would benignly fill any power void left by America. In such a world, deterring the use of force as a policy option would remain paramount. Deterrence is achieved through credible military capabilities, political resolve and, more often than not, alliances that complicate and overwhelm any opportunistic use of force. Deterrence is the starting point for any defensive national strategy.

A self-reliant Australia would have choices in how it achieves deterrence. The spectrum of deterrence options extends from neutrality to nuclear weapons. The most recognised example of neutrality is Switzerland’s armed neutrality. This is supported by more than 90 percent of its people, while defence costs less than 1 percent of its GDP. Although Switzerland’s approach has worked in a geopolitical sense to date, it is challenged by pressure from allies during crises to align with such policies as sanctions on Russia and by emerging security threats, such as cyber.

Nuclear weapons and the policy of mutually assured destruction have helped ensure there have been no global conflicts since 1945. Russian threats to employ nuclear weapons also appear to have restrained further escalation by other nations in Ukraine. The grim reality is that nuclear weapons remain the ultimate deterrent. However, these weapons are expensive to build and maintain, and a decision to acquire nuclear weapons is not straightforward or guaranteed.

Australia could consider each of these options. How a neutral or a nuclear-armed Australia would be accepted in our region is an open question. Whether the Australian public could be convinced to go down either path is doubtful. Domestic opinion will probably remain somewhere on a middle path. Australia would need greater self-sufficiency or a revised alliance framework without American military capability as a backstop. Defence self-sufficiency would not come cheaply and could not be achieved without a defence budget beyond 3 percent of GDP. It is impossible to determine the precise requirement, but it is sobering to note that Australia’s defence budget in 1942–43 was 34 percent of GDP.

A revised alliance framework could help mitigate costs. It would also bring the advantages of burden-sharing, enhanced mass and breadth, and more significant strategic complications for adversaries. Beyond the US, our traditionally nearest and most predictable military partners are New Zealand and Papua New Guinea. However, they each spend less than 1 percent of GDP on defence. They offer limited practical capability in either scale or deterrence. Indonesia will remain an important partner, but our relationship with it will—for historical and cultural reasons—continue to wax and wane.

Further afield but closely linked to our region and interest in the status quo is Japan. It has a credible military force, and the national and military relationships with Japan are developing strongly. There is good potential for an alternative alliance here. Our relationship with India is less well developed. India’s strategic worldview is also less aligned with ours than Japan’s is. There is potential with India, but building a trusting relationship with it will likely be slower.

We could look at the possibility of working more closely with Singapore, which is well armed for its population of 6 million and is highly skilled in regional statecraft. Our former closest ally, Britain, remains a trusted and capable partner, but it is far from our region and must remain focused on European concerns.

These are a few obvious options for a new alliance framework. No combination will replace the US military’s global reach and scale (including its nuclear capabilities) or capacity for deterrence. Nor could the new alliance replicate the Five Eyes intelligence apparatus in any reasonable timeframe. Australia’s relative security position would be degraded without US military backing.

What, then, would Australia need to prioritise in defence policy if it judged that the US was no longer a reliable ally?

The two key elements of military capability are the ability to shield (defend) and to strike (attack). Each requires a third element, intelligence, to be effective. Australia would need to enhance all three to be more self-sufficient. None would come cheaply in dollars or workforce. Typically, these capabilities take decades to establish. Building them up would require bipartisan agreement through successive government terms of office. In all three, we would be better off maintaining the US alliance through thick and thin. But let’s imagine what we’d do if we were unsure of the alliance, as follows.

Intelligence would require new trusted partners and additional technical and human capabilities for collection and analysis. AI will help but will demand ever-larger supercomputers and data centres. The workforce is specialised and complex to scale, let alone quickly. With national resolve, we could be more capable in a decade.

Concerning shielding, strategically, we would have to decide whether to defend forward (in our near region) or back (on our home shores). Either would have implications for our close neighbours.

Regardless of that choice, we would have to step up preparations that we are already undertaking. Critical infrastructure and locations already require hardening from physical and cyber threats. We need proven air and missile defence capabilities such as Patriot and THAAD ( both, incidentally, US systems) and an ability to integrate them. In a policy and coordination sense, we require a national alert system for air and missile threats and enhanced capabilities to counter sabotage, subversion and espionage within Australia. All this would become more important if the US alliance looked unreliable.

Similarly, additional strike options and weapons holdings are necessary and would be all the more so if we needed to be more self-reliant. The current Guided Weapons and Explosive Ordnance program to expand our domestic munitions-production capability is worthwhile but needs additional funding and acceleration.

Greater reach, particularly to strike targets from the air and sea in the maritime domain, and an ability to fight for protracted periods are key. It would be expensive to buy additional weapons and platforms (such as aircraft and ships) and to make genuine effort to expand domestic production. Increased domestic production is already necessary, and more of it would be needed for greater self-reliance.

Nuclear submarines are essential to our deterrent posture, because they most credibly contribute to intelligence, shielding and striking. Their full cost is still being realised but they do more to complicate an adversary’s strategic and tactical calculations than any other kind of platform. Walking away from the effort to acquire nuclear submarines (if we could) would undermine our greatest deterrent.

If we are determined to achieve greater maritime reach and influence, the debate about Australian aircraft carriers should be revisited. Again, the cost of these ships would be significant, and having an ally that might deploy a few in our region would be very attractive.

Autonomous air and sea systems offer potentially more cost-effective surveillance and shield and strike options. We already need to incorporate more of these with greater urgency. Even more of them would be part of an Australian Defence Force that might have to stand without the US.

We are already in a world where almost nothing happens without some ability to maintain our operations from space. Satellites and the ability to protect them are increasingly essential (and expensive) capabilities in which we are underinvested. A shift away from the US alliance would necessitate very substantial investment here.

These are only a few of the most critical areas for consideration in a more self-sufficient defence posture for Australia. If we broke our alliance with the US for any reason, we would need to increase defence spending enormously to maintain credible deterrent forces.

A final point should be emphasised: a move away from our alliance of more than 70 years—and a military partnership founded in World War I—should not result from the term of office of just one erratic US administration. The ramifications for Australia would be profound.