Australia and New Zealand have a proud history of shared military endeavour. Over more than a century, from the shores of Gallipoli to the sands of Iraq, Australian and New Zealand troops have fought side by side. But spine-tingling evocations of past glories neither recognise nor explain the reality of the Australia–New Zealand alliance today. With the strategic balance teetering in the Asia–Pacific, a more cold-hearted assessment is needed.

Although both countries share the goal of peace and security in a rules-based world, they pursue that goal with very different intensities. Australia systematically accepts higher costs and risks than New Zealand does. New Zealanders each contribute NZ$426 to their defence; Australians spend A$1,438.

New Zealand doesn’t match Australia’s effort because it knows that Australia will shoulder the burden, at least in the local region. In exactly the same way, Australia relies on the US to shoulder the burden in the broader region. Lest there be any doubt of the pattern of reliance down the alliance chain, in recent times the US has spent around twice the share of its GDP on defence as has Australia, and Australia has spent more than twice the share as has New Zealand.

The disparate level of effort extends to each country’s response to China’s rise and to each country’s support for the US role in the region. New Zealand takes fewer risks of incurring Beijing’s ire than Australia, and Australia openly endorses the US role in the Indo-Pacific while New Zealand avoids the subject. It’s clear what’s happening: Australia is betting on a continued US role in the region—and its 2016 Defence White Paper says so—but New Zealand is keeping its options open.

In the coming years, both countries will have to tread a fine line between Donald Trump’s unpredictability and Xi Jinping’s threats of economic punishment. The antipodean pair could either draw closer together or be pulled apart. It’s impossible to say where each will be in five or 10 years but, as the least committed of the pair, New Zealand is at greatest risk of becoming a Western ally with Chinese characteristics.

Consistent with Australia having a larger economy and greater willingness to spend on defence, it has a larger and more sophisticated defence force than New Zealand. In terms of the assistance that each can render to the other, New Zealand gains the most. Based on the ratio of personnel numbers, New Zealand gains a sixfold increase in available military capacity, while Australia gains only a one-sixth boost. Both countries plan to spend more on defence over the coming decade, but that won’t alter the burden-sharing picture.

Despite the asymmetry of gains, Australia has a strong incentive to nurture its alliance with New Zealand. Apart from the geopolitical optics of keeping New Zealand onside, Australia would have to increase its defence spending by more than $1 billion a year to generate the additional military capabilities that New Zealand can contribute for operations. From Australia’s perspective, the business case for the alliance isn’t diminished one iota by the asymmetry of gains or the disparity in burden-sharing. All that matters is that the alliance delivers a net gain to Canberra.

Ongoing engagement between the ADF and NZDF is essential to maintain the alliance and maximise its benefits. Following a joint review in 2011, an expanded framework for cross-Tasman defence cooperation was established. But an expanded framework isn’t the same thing as expanded cooperation, and the growing technological gap between the ADF and NZDF will only make things more difficult.

Treaties are static documents, but alliances are living relationships. A conscious effort is needed to stop the relationship from becoming stale and, more critically, to bolster it against buffeting from a region in strategic transition.

It’s sobering to see how far expectations have fallen for the cross-Tasman alliance. The 1986 Dibb report argued for ‘the maximum possible interoperability of equipment between the armed forces of the two countries’. Within 12 months, a memorandum of understanding was signed for the Anzac ship project. Thirty years later, defence relations remain cordial and multifaceted, but there’s nothing like the Anzac project on the horizon to generate a sense of shared purpose.

At the same time, the interoperability of the two defence forces has eroded because of diminishing equipment commonality and divergent levels of sophistication. The situation won’t be rectified any time soon: in 1986, Australia spent eight times more on defence than New Zealand; today it spends 17 times as much.

The key is to find areas of common interest and commence joint activity that’s affordable to both parties. With that in mind, here are two suggestions for how Australia and New Zealand can work together to build a stronger alliance.

First, the two countries should expand combined military exercises in the region. Australia’s 2016 Defence White Paper set out an ambitious program of international defence engagement and combined exercises across the Indo-Pacific. Wherever possible, Australia should involve New Zealand in the expanded program. Priority should be given to two areas: combined exercises involving the US, and humanitarian assistance and disaster relief exercises in Southeast Asia and the South Pacific.

Second, Australia and New Zealand should consider combining their maritime surveillance efforts. Both countries have a vital interest in having an accurate picture of the local maritime environment. By pooling physical assets and fusing data, both would  gain. Faced with a similar problem, Canada and the US formed the North American Aerospace Defense Command (NORAD). Australia and New Zealand could follow this example, but with a focus on surveillance rather than air defence. The resulting Anzac Maritime Surveillance Command would be a ‘static’ capability that’s largely immune to the vagaries of politically contentious deployments.

The critical question is what New Zealand will be able to bring to the table. A good start would be to follow Australia and replace its P-3 Orion maritime patrol aircraft with the P-8 Poseidon. Better still, it could buy one or more Triton long-range surveillance drones to augment the system that Australia is acquiring.