A defence treaty with PNG might seem like a ‘win’ for Australia. But there are 4 crucial questions to answer

Today, Australian Defence Minister Richard Marles began negotiations with his Papua New Guinean counterpart, Billy Joseph, on a defence treaty. This builds on the bilateral security agreement signed between the countries in 2023.

Analysts have been quick to link the new defence treaty with Australia’s anxiety about China’s increasingly visible presence in the Pacific region.

This reflects Australia’s longstanding anxiety about powers with potentially hostile interests establishing a foothold here.

Because it’s only three kilometres from Australian territory, PNG has always been a particular concern. TB Millar, one of the architects of modern Australian strategic policy, went so far as to observe in 1965 that:

if the whole island [of Papua New Guinea] were to sink under the sea, the net result for Australia in terms of military strategy would be a gain. It is an exposed and vulnerable front door.

So, the possibility of a defence treaty seems like a “win” for an Australian government keen to bolster its security credentials in the frantic months before the federal election.

But the government needs to have good answers to four questions before it signs on the dotted line.

1. How will Australia enforce the treaty?

Although treaties are theoretically legally binding, there are very few practical enforcement mechanisms.

The constant agonising in Australia about whether the United States will meet its obligations under the Australia, New Zealand and United States Security Treaty (ANZUS) exemplifies this.

The Trump administration’s actions also illustrate how quickly a change of government can switch foreign and strategic policy directions, including obligations under longstanding treaties. Like ANZUS, the risk of unenforceability of the PNG treaty is higher for Australia. Australia’s anxieties about China mean that it needs the treaty more than PNG does.

Sanctions are the most likely way Australia could try to enforce the treaty if, say, PNG breached it by striking a security deal with China. But sanctions can be ineffective.

Alternatively, Australia could threaten to withdraw its support if PNG breached the treaty. But this is also unlikely because Australia knows China is likely to step into any gap.

This has been demonstrated in Solomon Islands. Even though Australia has a security treaty with Solomon Islands and invested A$3 billion in the 2003–17 Regional Assistance Mission, Solomon Islands still signed a security agreement with China in 2022.

2. Has Australia mitigated any risks?

No previous Australian government has offered PNG a binding security guarantee.

In 1977, Australia and PNG adopted a formal defence relationship. Australia, however, was cautious about instability in PNG and the risk of being drawn into a conflict along its land border with Indonesia. As such, it didn’t provide a commitment to defend PNG.

In the mid-1980s, PNG requested a defence commitment from Australia. Again, Australia was reluctant. As then-Defence Minister Kim Beazley recalled, PNG was “right in the frame of our relationship with Indonesia”, due to the shared border with Indonesia and the challenge of West Papuan independence activists crossing it.

As a compromise, the two countries made a Joint Declaration of Principles in 1987 that only provided the two governments “will consult … about matters affecting their common security interests”.

As the self-determination struggle in West Papua continues, PNG currently has defence units posted on its border with Indonesia.

Under what circumstances, if any, would Australia provide military support to PNG if violence on the border worsened? And what impact would this have on our relationship with Indonesia?

Not responding to a call for support from PNG could damage Australia’s reputation in the region. But if Australia did become involved in a conflict, it may be criticised for supporting activities that breach human rights.

The risk of Australia being unable to respond to a PNG request for military assistance is high because Australia does not have the defence (or policing) capacity to defend or stabilise a sprawling country like PNG.

Australia’s reliance on US assistance to stabilise Timor-Leste after its 1999 independence referendum illustrates the logistical challenges it faces when making large deployments, even in the region.

While Australia’s defence capabilities have improved since then, it would still likely only have the capacity to secure key cities in PNG and evacuate Australian citizens if there was serious unrest.

3. Can Australia justify the cost at home?

Australian taxpayers – already experiencing cost-of-living pressures – need to be told what funding commitments the government is willing to make to facilitate the treaty negotiations.

Australia’s promise of A$600 million to fund a PNG team in the National Rugby League is already attracting opposition at home.

4. What are the long-term defence plans?

PNG’s strategic location means Australia and the US have long had designs on establishing a permanent military base there.

Manus Island, for example, has been identified as an ideal submarine base. With Australia developing nuclear-powered submarines under the AUKUS partnership, are there plans to eventually base – or at least resupply – Australian submarines there?

This could have an impact on Australia’s relationships in the broader Pacific Islands region. There are already concerns in the region about whether the nuclear-powered submarines will comply with Australia’s obligations under the South Pacific Nuclear Free Zone Treaty.

Australia has legitimate strategic interests in PNG. As such, it’s understandable why a defence treaty is tempting.

But for 50 years, Australian governments have resisted this temptation because they decided that the risks outweighed the rewards. The current government will need to provide a good justification for its change of course.