More than the Sum of its Parts: Developing a Coordinated U.S.-Australian Response to Potential Chinese Aggression

Alliance Future: Rewiring Australia and the United States

The Carnegie Asia Program’s “Alliance Future” project aims to ensure that Canberra and Washington are working to operationalize and integrate their alliance in new ways. The project explores how to undertake difficult reforms, forge new modes of cooperation, harmonize outdated regulations, better align national strategies, address sovereignty concerns and risk thresholds, and ultimately reform the alliance for a more competitive era.

Introduction

Backed by its growing military strength, China has increasingly engaged in coercive and belligerent behavior in the Indo-Pacific region.¹ Beyond its frequent use of gray zone tactics to harass and intimidate neighbors, the People’s Republic of China’s (PRC) territorial claims have heightened fears that it might start a war to subjugate Taiwan or forcibly seize disputed features in the East or South China Seas.²

The 2022 United States National Defense Strategy (NDS) identified competition with China as the nation’s priority challenge and recognized that U.S. forces alone cannot successfully deter or, if necessary, defeat Chinese aggression. The U.S. NDS categorizes allies and partners as “a center of gravity of the strategy” and an asymmetric American strength.³ Similarly, the Australian 2024 National Defence Strategy makes deterrence by denial the priority mission, and echoes the conclusion of the Defense Strategic Review that the Australian Defence Force (ADF) is currently “not fully fit for purpose.”⁴ The Ministry of Defence also maintained that “Australia must work even more closely with our international partners” and that it would “deepen and expand” military cooperation with the United States.⁵

To realize these goals, Australia and the United States have agreed to work together to co-produce munitions through Australia’s Guided Weapons and Explosive Ordnance Enterprise (GWEO).⁶ Additionally, AUKUS, the trilateral arrangement between Australia, the United Kingdom, and the United States, will provide nuclear-powered attack submarines for Canberra and enhanced technological cooperation among the three allies.⁷ Although American-Australian military cooperation appears to be rapidly deepening, true strategic integration, which is critical for all other forms of military cooperation, remains inadequate.

Becca Wasser and I defined strategic integration between allies as a “common understanding of threats and prioritization among them and a coordinated division of labor for responding to these challenges.”⁸ Strategic integration is the most difficult type of cooperation to achieve—particularly in peacetime—given that each nation has its own interests and desire to protect its sovereignty. The strongest form of American-Australian strategic integration—a firm and public precommitment to combined defensive operations—is not likely feasible given political realities. However, even less formal forms of strategic alignment can enhance the credibility of combined deterrent threats and help to ensure that other forms of military cooperation support the objectives identified at the strategic level. A shared understanding of threats, roles, and responsibilities among alliance partners should shape other forms of institutional and tactical cooperation, so that every level of effort works towards shared goals. For instance, Canberra and Washington would ideally agree to co-develop and co-produce weapons that each party would need in priority scenarios, such as maritime strike and air defense missiles.⁹ Similarly, combined exercises should practice operations that are relevant to priority scenarios, and Australian and American forces should assume their likely roles and practice operating together as envisioned by plans.

Yet strategic integration does not require perfect alignment of priorities and a precommitment to respond. Rather, the United States and Australia together need to explore the military challenges that they could face and have honest conversations about their interests, capabilities, and constraints so that both parties have a better understanding of collective goals. A routine and frank strategic and operational dialogue will enable Washington and Canberra to identify similarities and differences between them, and to develop workarounds, so that they can develop combined response plans to potential crises based on viable and realistic assumptions. Any alliance plans could have multiple variants and be conditional. Additionally, senior Australian and American leaders would certainly need to decide during a crisis to implement them. More likely than not, any of the off-the-shelf plans would need to be significantly modified because of unexpected developments. These plans may not be entirely “worthless” as Dwight Eisenhower declared. But as the former president noted it is the act of planning that is truly important because it enables a faster well-thought-out response. Combined planning would force Australian and American officials to be “steeped in the character of the problem” and truly enable them to quickly develop a sensible response based on an actual crisis, which will be different from what the plans envisioned.¹⁰

Since the end of the Cold War, American and Australian forces have frequently operated together in the Middle East. However, these conflicts differ significantly from one with a great power like China with a large conventional force and nuclear weapons arsenal. Against these threats posed by state and non-state actors in the Middle East, the United States’ response planning only began after a crisis emerged. Typically, the United States cobbled together a coalition, which eventually agreed upon a strategy and operational plan. This process often took weeks if not months. After Saddam Hussein invaded Kuwait in August 1990, the United States had a luxurious five months to assemble a coalition, build up forces in the region, and develop a plan to liberate Kuwait.¹¹ In Operation Allied Force, the 1999 North Atlantic Treaty Organization’s (NATO) air war against Kosovo, the alliance would only agree to a graduated air campaign. When that strategy failed to compel Serbia to back down, NATO member states engaged in painstaking negotiations and General Wesley Clark, the Supreme Allied Commander, had to get alliance approval to strike potential targets.¹²

If China engaged in a war of aggression, the United States, Australia, and other nations would not have much time to develop a coordinated response. A swift military response by the United States and Australia would be essential in halting Beijing from achieving its objective. Otherwise, both countries face the prospect of having to roll back China’s territorial gains. Ideally, the allies would already have a good appreciation for each other’s capabilities, a shared and deep understanding of the problem, plans for how to respond, and an agreed-on military command structure for combined operations. Currently, despite significant apparent alignment between Australia and the United States’ defense strategies, there are fundamental differences between the two allies.¹³ Many of the concrete steps taken to deepen American and Australian military cooperation in the last few years have occurred in the absence of a foundational understanding of how the two militaries might work together to deter aggression in the Indo-Pacific region.¹⁴ It is therefore imperative that they begin having these conversations and developing these plans now.

This chapter considers the issue of how the United States and Australia can deepen their strategic integration to counter Chinese aggression. It lays out three different scenarios and outlines a plausible division of responsibility between American and Australian forces based on each parties’ interests. I select three possible but hypothetical scenarios of Chinese uses of force: a full-scale invasion of Taiwan at some unspecified date in the future, an attack on Second Thomas Shoal in the near term, and gray zone coercion against Australian forces in the Coral Sea in the late 2020s. These scenarios were chosen because they differ significantly in terms of where the aggression occurs, and the varying levels of strategic interests for Washington and Canberra in each situation. Each of the following three sections broadly outlines the following: a scenario in which China attacks or harasses an area that is “strategically” important to the United States and Australia. Then a plausible defensive plan that identifies roles and missions that American and Australian forces would undertake to counter hypothetical Chinese attack in the Indo-Pacific.

The final section of this report considers how Canberra and Washington can develop a unified approach to strengthen deterrence in all situations and move towards a division of labor that enables them to leverage their strengths and compensate for weaknesses.

1. Taiwan Invasion Scenario

While China invading Taiwan is not as likely as other forms of coercion such as gray zone attacks, the United States Department of Defense has identified a full-scale invasion of Taiwan as its “pacing scenario” due to the magnitude of the operational challenges and strategic consequences.¹⁵ It is therefore the benchmark that American forces are ultimately measured against, and is the driving force behind U.S. operational planning, modernization efforts, and posture.¹⁶ A large-scale amphibious and airborne assault on Taiwan would be an incredibly complex undertaking, but Taiwan’s proximity to mainland China and distance from the United States and Australia is a fundamental reality that will be difficult to overcome in the event of an attack by the People’s Liberation Army (PLA).

Beijing maintains that Taiwan is a part of the People’s Republic of China and that eventually Taipei must submit to rule by Beijing, preferably peacefully. If Taiwan seeks to declare its independence or refuses to accept future rule by the PRC, Beijing has made it clear that it is willing to use force to compel Taipei’s submission.¹⁷ Since 1979, the United States has maintained a policy of strategic ambiguity toward Taiwan in which Washington provides defense articles and services to Taipei, but does not have an ironclad commitment to defend the island in the event of a PRC attack.¹⁸ Although formal U.S. policy remains unchanged, President Joe Biden has several times stated that the United States would defend Taiwan should China attack.¹⁹

I make no judgment about the likelihood of an imminent Chinese invasion of Taiwan, which is a hotly contested issue. There is no doubt, however, that the modernization of the PLA is shifting the balance of power in East Asia. This modernization has emboldened Chinese forces to take aggressive actions throughout the region, and increases the odds that the PLA could successfully undertake such an audacious operation.²⁰ If Beijing is convinced that the pathway to peaceful unification is closed or will not occur in a timely fashion, it might gamble on an all-out invasion of Taiwan.²¹ The most difficult Taiwan invasion scenario involves the PLA undertaking a large-scale attack in an effort to quickly conquer the island—a territorial fait accompli—before Taiwan’s international partners can intervene.²²

The PRC’s attack would likely begin with multi-domain precision strikes—what the PLA calls a Joint Firepower Campaign—against key Taiwanese military forces, U.S. bases in the region ,and American naval forces inside the second island chain.²³ At the same time, the PLA would use cyber, electronic attack, counter space capabilities, and information operations to degrade the United States’ intelligence, targeting, and communications, in the hope of disconnecting and disorienting American forces.²⁴

An initial large salvo of ground-based ballistic and cruise missiles is likely to knock out most of Taiwan’s air defenses and would limit the ability of American fighter aircraft to effectively operate at scale. As a result, the People's Liberation Army Air Force (PLAAF) would likely have air superiority over the strait and Taiwan and would continue to use airpower to weaken Taiwan’s defenses by picking off remaining forces and directing sea- and ground-based fires against priority targets.

The People's Liberation Army Navy (PLAN) would aim to isolate Taiwan from the rest of the world with a joint blockade campaign, so that Taipei cannot rally international support, and to prevent supplies and arms shipments from reaching the island. The PLA’s blockade operations would entail cutting internet cables, strikes against ports and airfields, and a traditional quarantine around the island.²⁵ At this point, the PLA would launch the joint island landing campaign by simultaneously sending its fleet across the strait to conduct an amphibious landing on Taiwan’s northern beaches, while its airborne and special operations forces conduct an airborne assault to secure key terrain including airfields, bridges, and ports. The troop transport ships would be escorted by the PLAN’s formidable fleet of advanced destroyers and cruisers.

 Defending Taiwan: Roles and Missions

An international effort to defend Taiwan would involve multiple, simultaneously occurring major military missions. Before the attack begins, there would be questions about conducting forward deterrent operations to dissuade Beijing from launching the invasion. Once the war has begun, however, there are three core operational tasks: stopping the invasion force, attacking military targets on the Chinese mainland, and defending rear areas. Given their interests and capabilities, Australian forces would likely focus on defending rear areas and perhaps send a symbolic force forward as a deterrent. For its part, American forces would focus on attacking the Chinese invasion forces and the suppression or destruction of key military capabilities in mainland China, should mainland strikes be authorized. This division of responsibility aligns with these countries’ interests and capabilities, with the United States responsible for offensive operations against PLA forces, while Australian forces would be responsible for defending key sea lines of communication and their own territory.

The ideal warfighting posture for American and Australian troops is in tension with the desire to forward deploy forces for deterrence.²⁶ Washington needs to distribute American forces across the depth of the theater to a more survivable posture to withstand a Chinese first blow. For allies like Australia, whose forces are far from the primary area of operations, they would have to decide whether to move forces forward as part of a demonstration to China that a multilateral coalition would oppose any invasion attempt. As Australia has a limited number of aircraft and ships, even if they survived an initial assault, it would be difficult to sustain and could not contribute significant combat power to front line operations. Moreover, forward deployment would degrade Australia’s ability to protect its homeland, as well as key sea lines of communication in the South China Sea and Indian Ocean. In this scenario, therefore, it is likely that Australia would make a minimal contribution to a forward deterrent operation, and instead signal its readiness by deploying forces in and around Australia to bolster homeland defenses and protect key maritime chokepoints.²⁷

After the Chinese start the invasion, American forces would need time to recover and reconstitute from the opening strikes and begin to effectively conduct offensive and defensive operations. A pure denial strategy focuses on defeating the invasion force by sinking ships, particularly those that are ferrying troops across the strait, and supporting Taiwanese forces by attacking any PLA troops that make it ashore. As the invasion fleet would be protected by screening forces consisting of PLAN destroyers, cruisers, and corvettes armed with advanced surface-to-air and anti-ship cruise missiles, most of the defensive firepower would initially come from attack submarines and standoff missile strikes.²⁸ American submarines would cycle in and out of the Taiwan Strait to sink PLAN ships. Even once Australia has its first Virginia-class attack submarine in 2032, the ADF likely would not focus its undersea forces on operations in the Taiwan Strait. First, this is due to the narrow topography and shallow waters of the strait, which enable only several submarines to safely operate in the passageway at a time.²⁹ Second, the Taiwan Strait is thousands of kilometers from HMAS Sterling, and transit takes days each way. An Australian nuclear-powered attack submarine (SSN) would need to make this long voyage to reload after expending its torpedoes. Since Australia has a very limited number of submarines, and only a few can contribute to strait operations, it is probable that the Royal Australian Navy’s (RAN) diesel Collins submarines and its Virginia-class SSNs would focus on patrolling the key south Pacific maritime sea lines of communication to ensure that PLAN forces cannot conduct distant operations and threaten Australia or other rear areas.

The second aspect of defeating the invasion force involves attacking the PLA lodgment and providing air support to Taiwanese defenders, as some PLA forces are likely to make it to Taiwan. Pressuring the lodgment and limiting the number of reinforcements that land on the beach would help to prevent a Chinese breakout. This could take the form of long-range missile strikes against the lodgment, or direct attacks from the air. Ideally, air attacks would be coordinated with Taiwanese forces to prevent friendly fire incidents and increase the accuracy of the strikes. Fighter sweeps over Taiwan would be necessary to escort the attacking force and prevent PLAAF aircraft from observing and attacking Taiwanese defense positions. As PLAAF fighters would control the airspace over Taiwan, fifth-generation stealthy fighters would be needed. Thus, U.S. Air Force F-22 and F-35 fighters operating in a distributed fashion and supported by tankers, would likely take the lead in providing air support to Taiwanese ground forces. Although Australia has three squadrons of F-35s that could participate in air operations over Taiwan, this is unlikely for several reasons. The Royal Australian Air Force (RAAF) F-35s would need to be integrated into U.S. Air Force distributed operations to survive PLA attacks, which would be very challenging, and would need American refueling and logistics support to support their deployment and operations. Moreover, their involvement would leave very few fighters to defend Australian bases.

If they were to be authorized, attacks on the Chinese mainland could enable the coalition to suppress Chinese airpower and degrade or destroy the PLA’s intelligence and targeting systems that are critical for long-range strikes.³⁰ Again, this mission would likely be undertaken by United States forces. The United States possesses a fleet of stealthy bombers capable of flying very long ranges, penetrating Chinese layered defenses, and delivering large payloads against Chinese military targets, including hardened and buried facilities.³¹ Additionally, non-stealthy American bombers may launch long-range cruise, or hypersonic missile strikes against some Chinese targets. It is doubtful that Canberra would ever authorize Australian attacks against China. Moreover, Australian aircraft lack the range and all-aspect stealth necessary for strikes against mainland China. While the RAAF has long-range air-to-ground cruise missiles, it does not have a bomber that can deliver the large salvo required to penetrate China’s integrated air defenses. Therefore, the RAAF would likely reserve these missiles for other operations, such as protecting the sea lines of communication, and potentially striking PLA bases on the disputed features in the South China Sea.

An additional consideration that must be discussed in American-Australian planning for this contingency, in general, but particularly for strikes against PLA targets on mainland China is the risk of nuclear escalation. Given its growing nuclear arsenal, China is likely to emulate Russia and threaten to employ a nonstrategic nuclear weapon in an attempt to deter the United States and other countries from intervening and from striking its territory. But the likelihood that China undertakes a limited nuclear attack in the early days of a Taiwan war remains low due to the plethora of conventional strike options available to it.³² The risk of China employing a nonstrategic nuclear weapon grows if the war becomes protracted as escalating may enable conflict termination on favorable terms.³³ Regardless, China’s growing strategic and nonstrategic nuclear weapons cannot be ignored. The United States and Australia must consider escalation risks of their actions, approaches to managing escalation, and factor these issues into their defensive plans.³⁴

The final mission is the protection of rear areas. Given ADF’s operational limitations and priorities, Australia would likely lead missions that include defending its own territory and protecting sea lines of communication to the north. By keeping most of its air and naval forces in the South Pacific, Australia would be able to bolster its defenses and challenge the PLA’s power projection in the south. It is also essential to protect Australian air and naval bases, which would be critical launch pads for American bomber and submarine operations. The PLA Rocket Force (PLARF) possesses dual-capable intermediate and intercontinental ballistic missiles that are in range of Northern Australia. Additionally, Chinese Guided Missile Submarines (SSGNs) and bombers could launch cruise missile attacks on northern Australian bases. While the PLAAF currently has a limited aerial refueling capability, one should expect its ability to conduct long-range bomber operations to increase over time as the H-20 bomber enters the force and more H-6s are made air refuelable. China may strike Australian bases particularly if they are being used to support American operations. Thus, Australia would need layered air defenses that include combat air patrols by its F-35 and F/A-18 aircraft, ground-based air defenses, and Australian missile defense ships that are positioned in the northern approaches so that they can intercept incoming Chinese missile salvos. These forces would be cued to incoming threats by Australia’s Jindalee Operational Radar Network (JORN) and the RAAF’s Wedgetail airborne warning aircraft.

Moreover, Australia’s maritime patrol aircraft, submarines, and over-the-horizon radar network would monitor its northern approaches and the strategic chokepoints of Malacca, Sunda, and Lombak. By taking the lead in collecting reconnaissance from multiple sources, fusing, and processing the information, Australia could enhance situational awareness and prevent Chinese forces from breaking out of the first island chain. Australia’s JORN can detect maritime and air objects out to 1,000-3,000 kilometers.³⁵ This would help to provide early warning of potential threats that would need to then be verified by other assets like the P-8, E-7, or high-altitude drones, and submarines. The diesel-electric Collins-class submarines, which have limited endurance, could loiter in the shallower waters around chokepoints to interdict any PLAN submarines or ships that try to pass by. If Australia has Virginia-class submarines, they can lurk in deeper waters watching for subsurface and surface PLAN assets.³⁶

Should the PRC invade Taiwan, Australia could make important contributions to the defense effort by defending bases and forces in the South Pacific and patrolling key maritime chokepoints, while American forces focus on defeating the invasion and attacking mainland China. There is a misconception that once the RAN has U.S. SSNs, it would be expected to contribute to offensive operations, which is neither feasible nor sensible.³⁷ In a large-scale war with China, providing base access and logistics support along with air defenses are hugely important operations that align with Australia’s core interests and its capabilities. 

2. Second Thomas Shoal

Chinese gray zone coercion against Philippine forces at Second Thomas Shoal—a disputed feature in the South China Sea—is already happening. The Second Thomas Shoal is a reef in the Spratly Islands that is claimed by both the Philippines and China. To protect its claims to the Second Thomas Shoal, which falls within its exclusive economic zone, the Philippines intentionally grounded a naval ship—the BRP Sierra Madre—on the reef in 1999. Since that time, the Philippines has regularly conducted resupply missions to the ship and has periodically rotated the crew stationed on the dilapidated outpost.³⁸ In 2013, China established a coast guard patrol in the vicinity of Second Thomas Shoal and began harassing Philippine resupply missions.³⁹ China’s Coast Guard and maritime militia presence around the shoal increased notably in 2022, and these irregular forces have used increasingly aggressive tactics in an effort to cut off the Sierra Madre. Previously, Chinese ships have played a game of chicken with the Philippine resupply boats, aggressively maneuvering towards them while demanding that they desist. In the second half of 2023, Chinese forces upped the ante further by often ramming the Philippine boats or firing water cannons at them.⁴⁰ In one incident, a Philippine sailor was injured by Chinese personnel wielding machetes and spears.⁴¹

The July 2024 agreement between the Philippines and China temporarily cooled down tensions around Second Thomas Shoal but did not permanently resolve the fundamental areas of disagreement.⁴² By early 2025, Beijing yet again accused Manila of attempting to build a permanent structure on the reef that would eventually replace the Sierra Madre, as the eighty-year-old ship is rapidly deteriorating. At the same time, Chinese Coast Guard, maritime militia, and PLAN ships established a consistent presence around the reef and resumed their harassment of Philippine resupply missions. Beijing has insisted that the Philippines stop “construction,” and has threatened to blockade the reef, forcibly seize the shoal, and remove the Sierra Madre. The Philippines has asked for American and Australian assistance in this crisis but has not officially invoked its mutual defense treaty with the United States.

Defending the Second Thomas Shoal: Roles and Missions

In this short of a major war scenario, the Philippines, United States, and Australia want to prevent further Chinese territorial gains in the South China Sea and uphold the status quo at the Second Thomas Shoal, but they are also seeking to prevent the crisis from escalating into a full-scale war. The core Philippine military missions in this scenario are manning the shoal, resupplying the Armed Forces of the Philippines (AFP) forces on the Sierra Madre, conducting surveillance of air and sea around the disputed reef, and conducting air and maritime exercises and freedom of navigation operations. In this scenario, the Philippines would remain responsible for manning and resupplying its manned outpost on the shoal, while the United States and Australia would likely provide only indirect support in the form of military assistance, surveillance, and by asserting their right to freely navigate through the South China Sea.

To date, Philippine forces have independently manned the Sierra Madre. There have been sporadic calls for the United States to establish a combined presence on the disputed reef with the Philippine crew, and to replace the rusting hull with a more permanent structure.⁴³ Either of these courses of action would be incredibly escalatory as it would involve the United States taking sides in the status of a territorial dispute to which it is not a party and where it does not formally recognize its ally’s territorial claim. China has already stated that the Philippines’ construction on the reef to reinforce the ship is a red line. However, those in favor of a combined presence argue that President Xi is aware the PLA is not ready to defeat U.S. forces, especially at such a distance from the Chinese mainland. It is also important to note that President Xi would also be weighing how he is perceived domestically, and that he has gone to great lengths to avoid appearing weak; therefore, he may not back down if American forces began to directly support the Philippines’ presence on the shoal.⁴⁴ Since Australia does not have a direct interest in the Second Thomas Shoal dispute or a mutual defense treaty with the Philippines, Canberra likely would not consider manning the reef. This mission is best left to the Philippines.

American or Australian naval or coast guard ships could directly participate in the resupply mission by transporting supplies to the Second Thomas Shoal or escorting Philippine cargo and personnel ships. Both courses of action increase the likelihood of direct confrontation. If China were to quarantine the shoal, resupply could involve running the blockade and forcing a showdown. It is, therefore, less escalatory and more likely that the Philippines remain responsible for maritime logistics support to the Sierra Madre, but the United States and Australian navies could train Philippine sailors how to engage in evasive maneuvers and teach them to defend against forcible search and seizures. Moreover, both nations may want to donate patrol ships that the Philippines could use for this mission. With a larger fleet, the Philippines could maintain a more persistent presence around the shoal in their effort to deter Chinese aggression.⁴⁵

The preferred way to provide food and other provisions to the crew on the Sierra Madre is by boat. But if aggressive tactics by Chinese ships prevent any Philippine ships from reaching the reef or through a full-scale quarantine-style blockade, supplies could also be air-dropped to the Philippine crew. In 2014, when China blockaded the Second Thomas Shoal for three weeks, the Philippines used airdrops to supply the crew trapped on the reef.⁴⁶ The Philippines also airdropped supplies as recently as 2024. From Washington and Canberra’s vantage point, it is better for the Philippines to maintain responsibility for the resupply mission. Should a blockade extend for a considerable amount of time, both nations could consider assisting the Philippines in this effort. Airdropping basic provisions like food, water, and medicine could be undertaken as a humanitarian mission. The PLAARF could contest an airdrop, but unlike at sea, it would be difficult for Chinese aircraft to persistently patrol the airspace around the shoal, which is far from the Chinese mainland. American or Australian airdrops would risk escalation as it would directly put their forces in a position where China may decide to interdict them, which is probably not in Australia’s interest. But the United States may be willing to run that risk due to its mutual defense treaty with the Philippines, while it is less likely that Australia would do so.

Simply knowing where Chinese ships are operating is a difficult challenge for the Philippines and is an area where the United States and Australia could potentially help. China’s PLAN warships are supplemented by the Chinese Coast Guard and the maritime militia vessels, which try to evade detection by blending in with commercial fishing vessels. The maritime militia, which is a state-sponsored paramilitary force, has been at the forefront of asserting China’s sovereignty claims through its dangerous maneuvers and low-level attacks against other countries’ ships in the South China Sea.⁴⁷ Chinese fishing vessels, whether truly commercial fishing mariners or maritime militia, seldom have their automatic identification system (AIS) transponders, even though they are legally required to do so.⁴⁸ Because of this obfuscation, identifying and tracking maritime militia vessels in real time is difficult, and as has been demonstrated at Second Thomas Shoal, the maritime militia can be called in as reinforcements by the Chinese Coast Guard.⁴⁹ To improve the Philippines maritime domain awareness around the Second Thomas Shoal, the United States and Australia could establish a multinational South China Sea surveillance center that fuses multiple different types of intelligence collected by satellites.⁵⁰ Additionally, Australia and the United States could periodically increase the presence of maritime patrol craft, crewed like the P-8 or uncrewed systems like the MQ-9B.

In this scenario, the ultimate mission is to assert the right to freely navigate in the South China Sea, and to bolster the Philippines with a combined show of force. Multinational exercises that demonstrate an ability to operate together with air and maritime forces identifying, tracking, and engaging potential hostile ships and aircraft in disputed waters upholds the right of free passage and demonstrates capability to resist.⁵¹ Both American and Australian forces, as well as other interested nations such as Japan, likely would participate in periodic training events and combined operations to strengthen deterrence.⁵²

In the Second Thomas Shoal, neither Washington nor Canberra has such interests at stake that they would want to be at the frontline of deterring Chinese aggression. Because China’s gray zone tactics are a persistent threat, it is logical for the nation being harassed to take the lead in countering them. The Philippines, therefore, likely would continue to provide forces to hold onto the Second Thomas Shoal, and Philippine boats and aircraft will continue to ferry supplies and personnel to the reef. Nonetheless, the Philippine forces are widely outmatched by the PLA and Chinese Coast Guard, and they lack the space or airborne surveillance capabilities and processing to closely monitor Chinese ships. The United States and Australia can signal combined resolve to uphold the status quo and resist unilateral efforts to forcibly seize territory by establishing a combined maritime domain awareness center and conducting occasional multinational exercises in the South China Sea.

3. Coral Sea Coercion

PLA forces have established a persistent presence in the South Pacific due to deepening cooperation with the Solomon Islands and by 2025 regularly harass Australian ships and aircraft operating in Coral Sea. In this hypothetical future scenario, China has established a military footprint in the South Pacific, and its air and naval forces have been engaging in the same sorts of gray zone coercion that have been so prevalent in the South and East China Seas. China’s interest in the South Pacific stems first and foremost from its desire to fuel its economic growth and secure access to the region’s resources, especially fish, minerals, and lumber.⁵³ In addition to promoting and protecting its economic interests, China’s pursuit of overseas bases aims to weaken existing alliances, while building associations that Beijing leads.⁵⁴

China’s expansion into the South Pacific began in April 2022 when Beijing signed a clandestine security pact with the Solomon Islands in which the two nations agreed to cooperate in the areas of security and law enforcement.⁵⁵ This agreement was leaked to the press and followed up in 2023 with the Solomon Islands awarding a Chinese state company, the China Civil Engineering Construction Company (CCECC), a contract to refurbish the port at Honiara and wharves in Makira and Renbel provinces.⁵⁶ Protestations by the government of the Solomon Islands that it would never allow China to use the island as a military base proved to be false.⁵⁷

In early 2025, even while construction at the port is still underway, PLAN ships increasingly make port calls at Honiara and Chinese fishing vessels and maritime militia increasingly ventured into the Solomon and Coral seas. As Chinese overwhelm the island to work on the ports, local resentment at the Chinese presence grew. In the spring of 2025, protests erupt against the pro-Chinese Solomon Islands prime minister.⁵⁸ Invoking the security pact with China, the Solomon Islands prime minister requests Chinese help in stabilizing the situation. Beijing responds by sending People’s Armed Police (PAP) as “peacekeepers” to help restore order to the capital.⁵⁹ The protests are quickly put down by the PAP, but the Chinese forces remain in Honiara and are soon joined by PLAAF fighters and drones, and a PLAN surface action group.

In addition to conducting illegal fishing, Chinese ships and aircraft begin to harass Australian military aircraft and ships operating in the northern approaches.⁶⁰ Chinese forces begin unsafe maneuvers in the Coral Sea by flying and sailing dangerously close to RAN and RAAF ships and aircraft. For example, a PLAAF fighter fires flares at RAAF P-8 aircraft conducting a routine patrol in Australia’s northern approaches, which is a tactic the PLAAF had used previously against Australian helicopters in the Yellow Sea.⁶¹ Such an uptick in Chinese harassment of Australian forces leads to near-miss incidents, such as a Chinese ship nearly colliding with Australian amphibious ships transporting American and Australian Marines for a combined exercise.

Coral Sea: Roles and Missions

In the Coral Sea scenario, Chinese gray zone tactics have grown in frequency and intensity against Australian forces. However, there is no territorial dispute in the Coral Sea, and this will impact the scope of a potential conflict in this scenario. As a result, the primary roles and missions would be to increase patrols of northern approaches, document and publicize illegal and unsafe Chinese behavior, and assert freedom of navigation in the hopes of deterring further harassment. Given Australia’s interest in this situation and the proximity of its forces, Australian forces would be responsible for guarding its northern waters and recording Chinese forces’ aggressive and irresponsible actions. At the same time, the United States would serve as the backstop for Australia’s routine patrols with an intermittent military presence, which would make clear Washington’s readiness to defend Australian forces against any Chinese hostility.

For Australia, an increased PLA presence could make Canberra vulnerable to military coercion, and it may need to defend its outlying islands and waters from Chinese aggression. Because the situation could pose a direct threat to Australian sovereignty, Canberra therefore would prioritize countering unfettered Chinese gray zone tactics. Moreover, the ADF is best positioned to respond to this harassment and to protect the freedom of the seas. Its ground-based over-the-horizon radar network, when coupled with airborne intelligence assets, enables the ADF to monitor the area while the RAN could increase its patrols of Australia’s northern approaches. Australia would need to expand the number of RAAF aircraft routinely deployed to its northern bases. The ADF could also deploy ground forces with long-range missiles and air defenses to protect these bases, also providing Canberra with the ability to hold nearby Chinese forces at risk. While the objective is to compel the PLA to stop its gray zone coercion without direct confrontation, it is important for Australia to have a credible threat of escalation. This is where periodic deployments of American bombers and ships, as well as combined exercises, could contribute to the underlying coercive threat.

Although the United States rotates Marines to the Northern Australia city of Darwin annually, and periodically deploys other forces for exercises to Australian air bases, the episodic nature of its presence does not lend itself to being the primary response force to day-to-day coercion by the Chinese. Additionally, Australian forces would take the lead in recording these incidents and share them with the international community. The United States could, however, supplement Australia’s intelligence with its space-based capabilities to help identify Chinese illegal actions and track force movements. Furthermore, U.S. Marines already deployed to Darwin might transit on Australian amphibious vessels and other RAN ships in the Arafura and Coral Seas. This type of combined naval presence already routinely occurs, so therefore should not be seen as escalatory, and the allies should continue this practice.⁶² This type of deep maritime integration also helps send a strong signal to China that the United States will support Australia. Generally, however, America would be supporting the ADF, which would take the lead in countering Chinese gray zone tactics.

Conclusion

The United States and Australia need to strengthen deterrence, which involves having the ability to defeat various types of Chinese aggression in different locations across the Indo-Pacific. American and Australian forces have a long tradition of working with other countries to counter shared threats, but China presents a much greater challenge than any recent adversary. Chinese military strength has grown to such a level that no one country—not even the United States—can match it alone. And China aims to achieve quick military victories that would be very difficult to reverse. Alliance planning before the war begins, rather than after, is essential. Although Australia and the United States’ defense strategies appear to be in lockstep, there remain considerable differences between the allies. But officials in Washington and Canberra likely do not fully appreciate these gaps and need to engage in a combined strategic and operational planning process to develop a shared understanding of where each stands.

Given that Washington and Canberra have different interests in the three hypothetical scenarios presented above, it is unsurprising that a divide and conquer approach in terms of who is in the lead for specific missions in different scenarios makes sense. Neither country has the capacity, or the capabilities postured at the right locations, to undertake all the missions in the three disparate locations. My proposed threat ranking for each ally and their assigned roles and responsibilities are detailed in the table below. Yet Australia and the United States do not need to close all the gaps between them to develop plans that will strengthen deterrence. Behind closed doors, Canberra and Washington need to broach these topics and draft combined response plans to enhance their responsiveness to any aggression.

There are many questions about whether Australia would join in a United States–led effort to defend Taiwan.⁶³ Ultimately, the Australian government at the time of an attack would make the decision about whether it was in Canberra’s interest to join the war. The government may be unwilling to join an anti-China coalition, or refuse to provide American forces with base access because of its deep economic ties to Beijing and vulnerability to Chinese long-range missile attacks.⁶⁴ In the proposed division of responsibilities laid out, however, Australian forces are not fighting Chinese forces in the strait, but supporting a multilateral effort by protecting the Australian homeland and key northern sea lines of communication. Australia is the rear guard, while American and Taiwanese forces are on the front lines.

In the South China Sea scenario, both Australia and the United States are interested in stopping Chinese territorial aggrandizement, but also do not want to end up in a major war over a disputed reef. Thus, they would both provide limited support to the Philippines, who will continue to take the lead in resupplying forces on the Second Thomas Shoal. The United States has more formal ties and interest in supporting the Philippines than Australia, and thus, would probably do more in terms of providing the conventional deterrent threat with its occasional military presence than Australia.

In the Coral Sea, Australia has the most at stake. Its geographic proximity to the main area of operations, naturally puts it in the lead for contesting Chinese gray zone attacks. The United States has a deep interest in defending Australia, but because the Coral Sea scenario does not center on a territorial dispute, there is less likelihood of immediate escalation. The United States would provide similar support that it provides in the Second Thomas Shoal scenario to Australia in the Coral Sea with an occasional military presence and combined exercises with ADF troops.

This paper is intended to stimulate conversation among academics, think tankers, and Australian and American government officials. It does not provide a definitive answer to what American and Australian forces should or would do in any particular scenario. For the U.S.-Australian alliance, these may not be the top three scenarios of interest, and my characterization of threat perceptions and preferred division of responsibilities almost certainly does not align with reality in either nation. Yet Canberra and Washington do not need the same prioritization of threats, a precommitment to an allied response, or even an agreement about their appropriate roles and responsibilities. Australian and American officials, however, must discuss and debate these issues in detail if they want to develop coordinated and practical plans for responding to Chinese aggression in the hopes of deterring it from occurring in the first place. If the alliance really is going to be more than the sum of its parts, Washington and Canberra must have difficult conversations in peacetime about their threat perceptions, and how they would coordinate their responses to specific Chinese attacks.