The extent to which the ANZUS Treaty turns upon the US provision of a nuclear umbrella to its smaller ally is a topic both complex and controversial. J.G. Starke opined that, while the treaty certainly didn’t prohibit resort to nuclear weapons in fulfilment of acting ‘to meet the common danger’, a simple test of proportionality meant the common danger would have to be virtually existential.

Some believe that Australia doesn’t face existential threats, and therefore that any US commitment to resort to nuclear weapons in defence of Australia is meaningless. Others have argued that the US has never provided any such public commitment anyway—that Australia has occasionally claimed such protection, but without any direct confirmation from a US president (the person who would need to approve the use of US nuclear weapons).

Moreover, the supposed nuclear relationship seems, at first glance, to find little expression in direct defence cooperation. There are no specific ‘nuclear sharing’ arrangements of the sort that the US has with some of its NATO allies, for example, under which the host country supplies and operates tactical-range delivery vehicles and the US supplies and controls the nuclear warheads.

But parts of that picture are misleading. The second clause of the Nixon Doctrine, for example, does offer a general nuclear assurance ^[1] to US allies in Asia. The joint facilities do constitute a unique and highly prized form of alliance nuclear sharing. Moreover, some readers will remember that the ANZUS alliance broke apart precisely over the issue of extended nuclear deterrence when New Zealand declared itself nuclear-free back in the mid-1980s—and interpreted that to mean that its own ally’s nuclear-powered or -armed vessels couldn’t enter the country’s ports or airfields.

Bob Hawke, the Australian prime minister at the time, underlined the policy difference between Canberra and Wellington, insisting that Australia couldn’t claim the benefits of nuclear deterrence if it wasn’t prepared to contribute to it.

But the ending of the Cold War, a decade of US unipolarity in the 1990s, and a subsequent focus on the ‘war on terror’ post-9/11 has meant that—in the intervening years—Australian policymakers typically haven’t had to spend much time contemplating issues relating to the nuclear side of the alliance.

That’s changing fast. Nuclear weapons may have been of marginal interest to Australian governments in the quarter-century following the end of the Cold War but, in recent years, that interest has returned with a vengeance, driven by a series of ominous geopolitical events: more competitive great-power relations, a rapidly shifting power balance in Asia, the apparent weakening of US commitment to its allies—and even to a liberal world order—under the Trump administration, and the growing risk of a more densely proliferated nuclear world (advertised by North Korea’s successes in its nuclear-testing and ballistic-missile programs).

The strongest evidence of a new, heightened, Australian engagement with the central questions of extended deterrence comes from the defence strategic update of 2020 ^[2], and the apparent rejection of US extended deterrence that unfolds there. With remarkable aplomb, the document notes that US conventional and nuclear weapons have been central to the deterrence of nuclear attack on Australia, but then abruptly states that Australia intends to become more self-reliant in deterring adversaries.

The text of paragraph 2.22 of the update carries weighty implications, suggesting as it does a willingness to move towards an independent Australian nuclear capability. The growth of Australian interest in long-range offensive strike capabilities seems to complement that shift in declaratory policy.

Both the shift in language and new interest in long-range missile technologies, including land-strike capabilities, suggest that some important judgements have been made behind closed doors in Canberra. Those judgements apparently concern the broader durability of the US alliance system in general, and the waning credibility of US extended nuclear deterrence in particular. But, if so, the government has been reticent about building a public consensus around those decisions.

Such reticence is understandable. For one thing, Australians aren’t used to thinking about nuclear weapons as direct contributors to the country’s defence; they’re more inclined to see them as abstract contributors to global order. Moreover, there’s certainly no bipartisan consensus on the question of an Australian nuclear-weapon program. Given that any such program would straddle decades, embarking on such a course in the absence of some degree of bipartisan consensus would probably be a recipe for failure.

Then there are the challenges the country would face in the diplomatic, technical and strategic realms. If it wished to build a nuclear arsenal, Australia would have to leave the Nuclear Non-Proliferation Treaty and abrogate the Treaty of Rarotonga (the foundation document of the South Pacific Nuclear Free Zone). It would need to acquire fissile materials, construct a safe, reliable nuclear warhead, and either build or purchase a delivery vehicle appropriate to its needs. And it would need a strategic policy that explained to potential adversaries, allies and neighbours just how Australia envisaged using its nuclear arsenal.

All in all, that’s a challenging set of policy hurdles. With a new administration in the White House, perhaps both allies will be more prepared for a serious discussion about extended nuclear deterrence and what comes after.

This post is an excerpt from ANZUS at 70: the past, present and future of the alliance ^[3], published by ASPI with support from the American Chamber of Commerce in Australia and edited by Patrick Walters.