The arms exporter Tokyo is becoming — and what it means for Southeast Asia

Japan’s shift to lethal arms exports marks a decisive turn in Southeast Asia’s security order, deepening regional divides while testing Tokyo’s ability to balance market competition with alliances.

Southeast Asia’s security landscape has never been as simple as the US-China binary suggests, but for decades, that binary provided its dominant logic: Washington as the primary guarantor for maritime states, Beijing as the dominant partner across much of the mainland.

Alongside that competition, middle powers like Australia, India, South Korea, and, above all, Japan have been quietly deepening their security footprints in the region, mostly through non-lethal means. But that will soon change in April 2026, as Japan’s decision to scrap its ban on lethal weapons exports changes the terms of that involvement decisively.

For years, Tokyo had been building a quiet architecture of defense relationships across the region through two main instruments. The first was a series of bilateral Defense Equipment and Technology Transfer agreements with the Philippines, Vietnam, Malaysia, and Indonesia. This created the legal framework for non-lethal equipment transfers before the export ban was ever lifted. The second was the Official Security Assistance (OSA) program, introduced in Japan’s 2022 National Security Strategy and launched in 2023, which enabled Japan, for the first time, to provide military aid directly to the armed forces of like-minded countries.

This was a meaningful distinction from its longstanding Official Development Assistance, which explicitly prohibited military use. OSA crossed that line, signaling that Tokyo’s conception of regional security cooperation was expanding. OSA’s first recipients were the Philippines, Malaysia, Bangladesh, and Fiji, and the program has since expanded to include Indonesia, Thailand, and East Timor, with approximately $116 million budgeted in fiscal 2026. This was a 125 percent increase on the previous year. Through OSA, Japan delivered coastal radar systems and patrol boats to the Philippines, rescue boats to Malaysia, and, in 2024, signed a Reciprocal Access Agreement with Manila to facilitate joint exercises and logistics sharing.

However, in April 2026, the ceiling on the scope of that presence changed. Specifically, on April 21, Prime Minister Sanae Takaichi’s cabinet approved scrapping Japan’s longstanding ban on lethal weapons exports. This decision opened the door to overseas sales of warships, missiles, fighter jets, and drones. However, exports remain limited to 17 countries with existing agreements, subject to National Security Council approval. Japan maintains a ban on transfers to countries at war, except in narrow cases affecting its own national security.

Wars in Ukraine and the Middle East have strained US weapon supplies and production, and stretched Washington’s commitments. Allies across Asia and Europe are diversifying as confidence in American guarantees wavers under the Trump administration. And Japan’s own defense industry, long limited to serving the Self-Defense Force, needed external customers to remain viable. As Takaichi put it: “No single country can now protect its own peace and security alone.”

From pacifist to arms supplier

The foundations were laid over a decade. Prime Minister Shinzo Abe’s 2014 reinterpretation of the Three Principles on Arms Exports allowed Japan to begin exporting non-lethal defense equipment to select partners. Early results were modest: patrol boats to Indonesia and Bangladesh, radar systems to the Philippines, and, in 2016, the leasing of five TC-90 trainer aircraft to the Philippine Navy.

This 2026 revision effectively removes five legacy export categories that had confined Japanese defense products to support roles: rescue, transport, surveillance, mine-clearing, and instead authorizes the transfer of complete weapons systems across air, land, and naval domains. This development is not a sudden break from pacifism, but rather the policy endpoint of a decade-long incremental shift.

The market Japan is entering

Japan’s biggest immediate deal is with Australia. On April 18, Tokyo and Canberra signed what is now Japan’s largest postwar defense export contract: Mitsubishi Heavy Industries will build the first three of a planned 11-ship fleet of upgraded Mogami-class frigates for the Royal Australian Navy, with the remaining eight to be constructed domestically by Austal in Western Australia. The initial three-ship contract is valued at approximately A$10 billion (US$7 billion), with the broader program potentially reaching A$20 billion over the decade. Australia selected Mitsubishi Heavy Industries over Germany’s Thyssenkrupp Marine Systems, not, as sometimes reported, over a South Korean bid. What made this deal incredibly unique was that, while it was agreed in 2025, the contract was only formally signed in April, signaling that the agreement was designed with Japan’s 2026 Arms export liberalization in mind.

In Southeast Asia, Japan is entering a market where South Korea already has a foothold. South Korea is the Philippines’ top defense supplier, with Korean-made systems including FA-50 light attack aircraft, frigates, and patrol vessels worth around $3 billion delivered over the past decade. Indonesia has purchased six Jang Bogo-class submarines from Korean shipbuilders and co-developed the KF-21 fighter with Seoul. Malaysia acquired 18 FA-50 aircraft in 2023. South Korea’s more explosive growth, though, has come from Europe, which includes Poland, Romania, Estonia, and Norway, driven by post-Ukraine demand. In Southeast Asia specifically, Japan is not displacing a dominant supplier so much as entering a crowded field that already includes South Korea, India, France, and the United States. That crowding matters for the alliance-management problem that arises later.

The growing division

The reception to Japan’s policy shift maps almost exactly onto Southeast Asia’s existing fault lines.

The impact of Japan’s policy shift is shaped by existing regional divides. Mainland states offer limited opportunities: Cambodia and Laos maintain close ties with Beijing. Thailand, though officially a US treaty ally, has been diversifying its arms purchases toward Chinese suppliers. Without serious maritime disputes, demand for Japanese naval platforms across most of the mainland is thin. Myanmar is excluded from Japanese arms transfers due to restrictions on exporting to conflict-affiliated areas.

Vietnam is the interesting exception. Historically reliant on Russian-origin equipment, it has been quietly diversifying toward Japan, India, South Korea, and the US as Moscow’s position weakens. A 2020 agreement for six Japanese coast guard-based patrol vessels was an early signal of that shift. But Vietnam’s Four No’s policy limits how openly it can engage with Japan, which is increasingly aligned with the US-led security architecture. Hanoi will take what it can get without being seen taking sides.

In contrast, maritime Southeast Asia is where Japan’s new posture will be most consequential. Indonesia is reportedly negotiating to acquire Mogami-class frigates, with four potentially constructed by state-owned shipbuilder PT Pal under a 2021 technology transfer agreement. Malaysia has deepened its defense partnership with Tokyo through bilateral agreements since 2018 and was among the first recipients of OSA. The Philippines has been the most openly enthusiastic: Defense Secretary Teodoro welcomed the policy change as a contribution to “regional stability through deterrence,” and Japan has already delivered 12 coastguard patrol vessels to Manila. Japan is also considering transferring decommissioned Abukuma-class destroyer escorts to the Philippines, though, as of late April 2026, no formal offer has been made, and discussions remain at the inspection stage.

Ultimately, maritime Southeast Asia, facing real Chinese pressure in the South China Sea, is gravitating toward a Japan-US security network. In contrast, mainland Southeast Asia, insulated from such pressures and economically integrated with Beijing, is not. Japan’s expansion of arms exports will not by itself create these divisions; they already exist, but the new export policy could deepen them, and ASEAN’s claim to regional centrality will bear the cost.

Market-alliance management

Japan is entering a market it helped build. A decade of quiet diplomacy, non-lethal transfers, and OSA grants has given it real relationships across maritime Southeast Asia. Now it arrives with far more powerful tools. The risk is proportional.

The instructive precedent is AUKUS. When the US, UK, and Australia announced their submarine partnership in 2021, France was not merely outbid; it was blindsided and shocked when Australia suddenly canceled the Submarine contract it had enthusiastically agreed to in 2016. Paris had treated its submarine contract with Canberra as the cornerstone of its Indo-Pacific strategy. What collapsed was not just a contract but a relationship that took years to rebuild. Paris recalled its ambassadors to Washington, London, and Canberra, an extraordinary diplomatic rupture between supposed allies. While diplomatic tensions were eased, the scars they left still affect confidence between France and its allies in the Indo-Pacific.

Japan faces an analogous risk. If Tokyo signs a defense deal with the Philippines or Indonesia that undercuts an existing arrangement with the US, a European partner, or South Korea, without prior consultation, it risks the same rupture. South Korea warrants particular care. It is simultaneously Japan’s most direct competitor in Southeast Asian naval and aviation markets and a critical security partner in any scenario involving China or North Korea. Their complicated bilateral history makes missteps here politically costly, extending well beyond the defense market. Whether Japan can compete with South Korea’s well-established export industry, which has a strong track record of timely delivery, remains to be seen. Japan must still demonstrate that it can be a dependable supplier as expected by its partners, especially given that delivery delays were among the key reasons Australia walked away from its submarine agreement with France in 2021, which triggered a diplomatic crisis.

US Ambassador to Japan George Glass called the export rule change a “historic step.” Washington’s enthusiasm is genuine. But enthusiasm from the top doesn’t automatically translate into coordination on the ground, and Japan’s defense ministry is now engaged in simultaneous discussions with multiple Southeast Asian partners. Managing those relations in market terms, without disrupting confidence among countries that rely on each other, will require diplomatic discipline Tokyo has not yet demonstrated at scale.

Japan spent a decade earning regional trust through restrained, non-lethal security cooperation. That credibility is now being staked on its transition to an arms exporter.

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This article reflects reporting and analysis made by The Southeast Asia Pacific Frontier. If you have additional context, a different take, or a perspective we’ve missed — whether you’re a researcher, a policy practitioner, or someone living with these realities on the ground — this is an evolving story and we’d like to hear from you. Drop a comment below or get in touch.