Canberra’s August 2025 announcement that it will purchase 11 upgraded Mogami-class frigates from Japan’s Mitsubishi Heavy Industries sent ripples through the Indo-Pacific. The deal, worth tens of billions, was not only Australia’s largest-ever naval procurement from a non-Western partner but also a powerful symbol of growing strategic trust between two countries once bitter adversaries.
For decades, Australia’s naval acquisitions leaned heavily on British or American designs, with occasional forays into European shipbuilding. Yet this decision to align with Tokyo over ThyssenKrupp Marine Systems of Germany reflected something bigger than ship specifications. The Royal Australian Navy (RAN) judged the Japanese proposal more compatible with its operational requirements — a vessel longer, wider, and armed with Tomahawk cruise missiles, integrated with advanced sensors, and designed for interoperability with allied systems.
It was a technical decision, but also a geopolitical one. And it raises the inevitable question: if Australia and Japan can cooperate on frigates, why not take the next step and co-develop the Indo-Pacific’s most pressing capability gap — a long-range, conventionally powered submarine?
This idea is not new. In 2014–15, Canberra seriously considered buying Japanese Sōryū-class submarines to replace its aging Collins fleet. That initiative collapsed by 2016 amid concerns over Japan’s lack of experience exporting defence technology, capability mismatches, and political resistance within Australia’s defence establishment. Instead, Canberra pivoted to France’s Naval Group, signing a contract for 12 Attack-class submarines — a program that imploded in 2021 after spiraling costs and delays.
That collapse cleared the path for AUKUS, the landmark trilateral agreement with the United States and the United Kingdom to deliver nuclear-powered submarines to Australia. But AUKUS itself has run headlong into industrial bottlenecks. The United States’ own shipyards are falling behind in delivering Virginia-class submarines to the US Navy, making it increasingly uncertain whether Washington can spare any boats for Canberra. The UK, while committed, faces capacity challenges of its own.
Former Australian foreign minister Alexander Downer captured the reality bluntly earlier this year: South Australia lacks the industrial capacity to build nuclear submarines, and if even the US is struggling to maintain production schedules, expecting Australia to master such a feat quickly is unrealistic.
This is not an argument against AUKUS. Nuclear-powered submarines remain the gold standard for endurance, stealth, and power projection. But as a complement to AUKUS — not a replacement — a jointly built, long-range, conventionally powered submarine with Japan could provide the Royal Australian Navy with a timely, credible capability.
The urgency of this idea stems from three overlapping developments:
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China’s naval surge. The People’s Liberation Army Navy (PLAN) is now the largest in the world by ship numbers, adding destroyers, frigates, and submarines at a rate unmatched by any other power. Its China Coast Guard, the biggest in the world, is employed for coercive “grey-zone” operations from the South China Sea to the Pacific Islands. Beijing is also testing intercontinental ballistic missiles over the South Pacific, underscoring the breadth of its strategic ambitions.
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US capacity limits. American naval shipbuilding is stretched to breaking point. The Columbia-class ballistic missile submarine program is consuming resources, while the Virginia-class production line is struggling to meet domestic demand. The United States’ ability to provide surplus boats to Australia — once considered a near certainty — is now in doubt.
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Japan’s transformation. Under Prime Minister Shigeru Ishiba, Tokyo is doubling defence spending, acquiring counterstrike capabilities, and loosening constitutional restrictions on military cooperation. Japan, once a cautious security partner, is emerging as a proactive regional power. Its naval technology has advanced dramatically, and its Mogami-class frigates and Taigei-class submarines are among the most sophisticated conventionally powered vessels in the world.
The convergence of these factors creates a narrow but significant opportunity: Australia and Japan can move beyond ad hoc defence cooperation and formalise a defence alliance anchored in joint capability development.
A codeveloped submarine program would achieve several goals simultaneously:
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Timeliness. A long-range conventional submarine could enter service years before Australia’s first nuclear-powered boat, filling a dangerous capability gap as the Collins fleet ages.
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Resilience. By diversifying its naval partnerships, Australia would hedge against potential reversals in Washington — especially if a second Trump administration scales back commitments to allies.
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Interoperability. Built with Japanese technology but aligned with US systems, the boat would fit seamlessly into allied operations across the Indo-Pacific.
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Industrial strength. Japan’s proven production lines offer a level of reliability that Australia has long sought but rarely secured in submarine construction.
As former US Deputy Assistant Secretary of Defense Elbridge Colby has argued, deterrence in the Indo-Pacific depends on allies willing to share risks and shoulder more responsibility. A joint Australia–Japan submarine would demonstrate precisely that kind of strategic imagination.
Critics might argue that such a project risks undermining AUKUS. But defence alliances are not mutually exclusive. The United States itself is a member of NATO, the Quad, and bilateral alliances across Asia. Each serves a different purpose, and together they reinforce deterrence.
AUKUS remains vital — especially its “Pillar Two” agenda on cyber, undersea systems, and advanced technologies. But Canberra must be realistic: if it struggles to secure even one Virginia-class submarine in the near term, and domestic nuclear construction lags, then a complementary program with Japan is not a betrayal of AUKUS but a bolstering of its credibility.
Washington, if pragmatic, should welcome the move. As the US defense industrial base strains under the weight of its own commitments, allies developing credible, interoperable alternatives are an asset, not a liability.
For Tokyo, too, the timing is auspicious. Japan has long been at the cutting edge of conventional submarine design, prioritising stealth, endurance, and advanced sonar capabilities to counter the PLAN in nearby seas. Its Sōryū and Taigei classes feature cutting-edge lithium-ion batteries, offering silent endurance that outpaces many rivals.
Domestic politics are also shifting. The Ishiba government’s decision to double defence spending over five years marks a historic departure from Japan’s postwar norm. The public, though still cautious, has shown greater acceptance of security partnerships, particularly with fellow democracies like Australia.
A joint submarine program would allow Japan not only to deepen its defence industrial base but also to institutionalise a new security partnership with Canberra. Beyond capability, it would signal Japan’s willingness to shoulder greater regional responsibility — a message that would resonate in Washington and across Southeast Asia.
The frigate deal of August 2025 is more than a procurement choice. It is proof of concept that Australia and Japan can align industrial capacity with strategic purpose. But to stop at frigates would be a wasted opportunity.
A formal defence pact, centred on a jointly developed submarine, could include:
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Mutual operational planning for contingencies in the South China Sea and Pacific.
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Joint training exercises, building habits of interoperability.
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Shared research and development in undersea warfare, cyber, and unmanned systems.
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If politically feasible, even mutual defence commitments, enshrining a bilateral guarantee akin to the US–Japan Treaty.
Such a framework would not replace the US alliance but reinforce it, weaving a tighter web of capable maritime democracies committed to a free and open Indo-Pacific.
Of course, this path is not without hurdles.
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Political sensitivities. In both countries, debates over sovereignty and industrial jobs could complicate co-production. South Australia’s powerful shipbuilding lobby may resist shifting too much work to Japan. In Tokyo, pacifist constituencies remain wary of deep military entanglements.
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Strategic balancing. Both nations must consider how Beijing would respond. A formal alliance, particularly one built around submarines designed for Indo-Pacific patrols, would be viewed as a direct challenge. Escalation risks must be managed.
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Technical alignment. Designing a truly long-range conventional submarine that meets Australia’s endurance needs without sacrificing stealth or cost will be a formidable engineering challenge. Lessons from the failed French Attack-class deal should serve as caution.
Yet none of these obstacles are insurmountable. What they require is political will, strategic clarity, and a recognition that the status quo — relying solely on uncertain AUKUS timelines — carries risks of its own.
If successful, the payoff would be profound. A jointly developed submarine would:
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Strengthen deterrence against China’s maritime coercion.
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Diversify Australia’s defence dependencies, reducing overreliance on any single partner.
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Embed Japan in a leadership role in regional security, moving beyond its traditional reliance on the US alliance.
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Send a message to Southeast Asia and the Pacific Islands that regional democracies are willing to act collectively to uphold rules and sovereignty.
It would also carry a symbolic weight. Eighty years after fighting each other across the Pacific, Australia and Japan would stand shoulder to shoulder as co-builders of one of the region’s most advanced weapons systems — a testament to reconciliation, trust, and shared purpose.
China’s fleet grows larger by the month. US shipbuilding falters. AUKUS strains under its own ambitions. Amid these shifting currents, Australia and Japan face a choice. They can treat the frigate deal as an end in itself, or as the foundation of something greater.
A jointly developed, long-range conventional submarine — embedded in a formal defence pact — would be more than a platform. It would be a statement: that middle powers are not passive spectators in the Indo-Pacific contest, but active shapers of its outcome.
