Abstract

In the context of growing tensions in the South China Sea–fueled by overlapping territorial claims and intensifying strategic rivalry among major powers–maritime security cooperation between Japan and Vietnam has become a critical element of their respective foreign and defense policies. This study investigates the principal strategic drivers underpinning the Japan–Vietnam maritime security collaboration in the South China Sea during the early 21^st century and evaluates its implications for the evolving regional security architecture. The analysis centers on the four primary mechanisms of cooperation: (1) high-level defense dialogues; (2) technical assistance and transfer of maritime equipment; (3) joint training programs and military exercises; and (4) collaboration in non-traditional security domains, including search and rescue, anti-piracy efforts, and disaster response operations. Of particular note is Japan’s intermediary role in enhancing Vietnam’s maritime security capabilities, undertaken with due consideration to Vietnam’s defense policy framework, especially the “Four No’s” principle. The findings indicate that the Japan–Vietnam maritime security cooperation is underpinned by a strategic alignment aimed at safeguarding freedom of navigation, countering unilateral actions, and reinforcing a rules-based regional order. Despite facing constraints such as institutional limitations, geopolitical pressure from China, and divergent strategic priorities, the partnership demonstrates resilience, sustained by a stable political foundation and mutual adherence to international law. These elements foster a conducive environment for deepening future cooperation and contribute constructively to the development of a flexible, inclusive, and rules-based regional security architecture consistent with the vision of a “Free and Open Indo-Pacific”.