Japan lifted its ban on exporting lethal weapons in 2026, opening the door to sales of fighter jets, missiles, and warships as Tokyo deepens defense cooperation with Vietnam in response to shared concerns over China's maritime assertiveness. The policy shift marks a significant expansion of Japan's security role in Southeast Asia, with Vietnam emerging as a key partner in Prime Minister Takaichi Sanae's updated Free and Open Indo-Pacific vision.
Takaichi chose Hanoi for her first major foreign policy address in May, pledging increased political, economic, and defense cooperation with ASEAN states to help them "acquire autonomy and resilience" amid intensifying geopolitical competition. The speech underscored Vietnam's strategic importance to Japan's regional security architecture.
From Cold War Isolation to Strategic Partnership
The transformation is remarkable. During the Third Indochina War from 1978 to 1991, Japan sided with China and the United States to isolate Vietnam because Hanoi had allied with Moscow. Japan's position reflected fears of Soviet expansion after Moscow increased troops on the Soviet-controlled Southern Kuril Islands to 6,000 in May 1978 and built up its Pacific Fleet into the largest of four Soviet fleets.
Japan signed a Treaty of Peace and Friendship with China in August 1978, including an anti-hegemony clause implicitly directed against the Soviet Union. It strengthened naval cooperation with the United States and participated in the Rim of the Pacific Exercise for the first time in 1980. Tokyo froze economic aid to Vietnam after Hanoi formally allied with Moscow in November 1978 and invaded Cambodia in December to topple the Khmer Rouge.
Japan conditioned aid resumption in April 1979 on Hanoi not establishing permanent Soviet military bases in Danang and Cam Ranh Bay, which Tokyo feared would threaten oil supplies from the Middle East. Japan didn't resume aid until 1992, after the Soviet collapse and the signing of the Paris Peace Agreements on Cambodia.
Economic and Defense Cooperation Accelerates
Since 1992, Japan's Official Development Assistance to Vietnam has totaled approximately $29.3 billion, the largest of any foreign donor. Japan is Vietnam's third largest investor and fourth largest trading partner. The two countries began low-level defense exchanges around the same time, with agreements on Japanese ships' port calls, joint search-and-rescue operations in the South China Sea, and training Vietnamese students at Japan's National Defense Academy.
In 2014, Japan agreed to provide Vietnam with six used vessels. Six years later it agreed to technologies for building military ships to boost Hanoi's maritime capability. In 2021, Japan signed an agreement with Vietnam to allow the transfer of defense equipment and technology. Vietnam falls under Japan's new Official Security Assistance under the 2022 National Security Strategy.
Vietnam established a partnership with Japan in 2002, a strategic partnership in 2009, and elevated Japan to Comprehensive Strategic Partner in 2023. Unlike with other Asian countries, Japan's World War II crimes don't cloud bilateral relations with Vietnam. Vietnam is now one of the most pro-Japan countries in Asia.
Maritime Security Drives Alignment
The rapid reconciliation reflects the compatibility of both countries' grand strategies. After the Cold War, Hanoi and Tokyo shared concerns about China's contestation of their maritime sovereignties. Vietnam began to look east to the sea, while Japan pivoted to the southern islands and treated maritime zones outside Northeast Asia as vital to its security. Japan supports combining the East China Sea and the South China Sea into a single theater of operation.
Joint statements show how the two countries' grand strategies evolved. Before China submitted its "nine-dash line" map to the United Nations in 2009, Japanese and Vietnamese leaders didn't emphasize maritime security in their joint statements, though there were low-level defense exchanges. Statements released by both sides in 2007 and 2008 didn't mention maritime cooperation, and economic cooperation was the main topic.
After Beijing's move, maritime cooperation became one of the key tenets of bilateral ties. Tokyo and Hanoi discussed maritime cooperation as a way to safeguard regional peace in joint statements issued in 2010 and 2011. The 2014 joint statement mentioned maritime security as an area of cooperation for the Vietnam-Japan partnership, the same year Japan provided Vietnam six vessels and one year after Japan protested China's declaration of an Air Defense Identification Zone over the East China Sea. The 2015, 2018, 2023 and 2025 joint statements also underlined the importance of maritime security.
Economic Resilience and Supply Chain Security
Japan's aid and military support to Vietnam are tied to that maritime focus. Japan wants to strengthen Vietnam's economic resilience in case China retaliates against Vietnam's maritime claims. Japan's ODA has helped Vietnam build manufacturing capacity and reduce dependence on Chinese investment under Beijing's Belt and Road Initiative. Japan has also pledged deeper cooperation on energy, critical minerals, semiconductors, supply chains and artificial intelligence.
Japan's transfer of naval technology, platforms and expertise to Vietnam is meant to secure South China Sea sea lanes and the flow of oil from the Middle East to Japan. A recent proposal to jointly develop fast landing crafts suggests Japan supports Vietnam's ability to hold and possibly retake offshore islands. Defense cooperation is expected to rise as Japan expands its OSA budget.
Strategic Benefits Without Great Power Constraints
Japan isn't a great power and can't defend Vietnam because of legal and material constraints, but Vietnam welcomes close maritime cooperation because it strengthens its multilateral foreign policy. Japan's constitutional limits on fighting overseas wars mean Vietnam can avoid the stigma of siding with one country against another, which is a principle of Hanoi's Four Nos doctrine. Japan's economic and military assistance also doesn't carry human-rights conditions or threaten the political authority of the Communist Party of Vietnam to the degree Western assistance can.
A close relationship with Japan also prevents Tokyo from seeing Hanoi's island reclamation activities as a threat to its sea lines of communication in the way it sees Beijing's activities. Vietnam supports Japan becoming a permanent member of the United Nations Security Council, a position China opposes.
On diplomacy, Japan's frequent port calls in Vietnam help build consensus and expectations for future U.S. port calls. Major U.S. Navy visits to Vietnam's ports are often preceded by Japan Maritime Self-Defense Force visits. Closer ties also let Japan deepen relations with ASEAN. Japan's opposition to unilateral changes in the South China Sea supports its case for condemning China's assertiveness in the East China Sea.
Beyond Maritime: Continental Cooperation
Bilateral ties will keep improving so long as Japan's and Vietnam's grand strategies remain aligned over the South China Sea. There's room to expand cooperation beyond the maritime sphere. At present, the Vietnam People's Navy and the JMSDF lead defense cooperation, while land forces have played little role. Japan should consider supporting Vietnam's continental objectives, including boosting Hanoi's land infrastructure to tighten connectivity with Laos and Cambodia and reduce their dependence on Chinese investment, exchanging views on how to use land forces in a maritime conflict, and developing weapons suitable for both continental and maritime domains such as missiles, drones and radars.
Why This Matters:
Japan's deepening partnership with Vietnam demonstrates how shared strategic interests can drive rapid alignment between former adversaries when both face common threats. The relationship offers Japan a cost-effective way to extend its security influence in Southeast Asia without the constitutional constraints that limit direct military engagement. For Vietnam, Japanese assistance provides critical maritime capabilities and economic alternatives to Chinese investment without the political conditions that come with Western aid. The partnership's focus on maritime security, supply chain resilience, and infrastructure development reflects center-right priorities: strengthening market-based alternatives to Chinese economic coercion, supporting allies' self-defense capabilities rather than direct intervention, and maintaining freedom of navigation through enhanced regional partnerships. As China continues asserting territorial claims, this model of cooperation between a constitutional democracy and a communist state united by strategic necessity may become increasingly important for regional stability and economic security.