Experts from 26 countries participated in Proliferation Security Initiative (PSI) Exercise Pacific Shield 25 (PS25) in Tokyo, Japan, from December 2-4, 2025. Participating States reaffirmed their commitment to take action and prevent the proliferation of weapons of mass destruction (WMD), their delivery systems, and related materials by State and non-State actors of proliferation concern. 

Since its establishment in 2003, PSI has proved an effective mechanism to enhance cooperation on disrupting illicit transfers of WMD-related materials and technologies. The PSI partnership has grown from 11 founding states into a flexible, voluntary, and enduring global counter-proliferation initiative endorsed by 116 states. PSI partners’ commitments and bias for action make the initiative a key component of the global framework against WMD proliferation and contribute to upholding international peace and security. The 2023 PSI High-Level Political Meeting (HLPM) Joint Statement at the PSI 20th anniversary also highlights how ‘...counter-proliferation efforts require greater awareness and collaboration amongst endorsing States in response to the recent challenges to the global and strategic security environment.’ 

PSI exercises improve structures for sharing intelligence, aligning decision-making processes, building capacity, and deploying capabilities and assets for interdiction operations. PS25 brings together regional and global counter-proliferation experts from the fields of security, defense, foreign affairs, border and export control and law enforcement. Exercises enhance regional counter-proliferation capability, coordination, and interdiction techniques and send a clear signal to proliferators that their activities are being monitored and PSI partners are prepared to take individual or collaborative action to prevent WMD proliferation. 

PS25 featured academic sessions and a table top exercise (TTX) that furthers the tenets of the HLPM Joint Statement, which stresses ‘the need for the PSI to address new and emerging proliferation practices, including proliferation finance involving cryptocurrency, intangible technology transfers,and the increasing sophistication of proliferators’ tactics to circumvent international law. Furthermore, PS 25 included live exercises conducted off the coast of the Boso Peninsula by the Japan Self-Defense Forces, the Australian Defence Force, the Republic of Korea Navy and Coast Guard, and the U.S. Navy and Coast Guard. PS25 also included port exercises in Tokyo Bay conducted by the Japan Coast Guard, Japan Customs, Ministry of Foreign Affairs, and National Police Agency. 

PS25 occurred against the backdrop of a dynamic proliferation threat environment. In this context PSI partners recognized the importance of all United Nations Security Council Resolutions (UNSCRs), including the longstanding resolutions on the DPRK, and recently reapplied resolutions on Iran. Participants committed to take all appropriate national-level measures to fully implement these Resolutions, especially those provisions relating to the interdiction, seizure, and disposal of prohibited items. Participants also recognized the importance of engaging PSI endorsers and non-endorsers worldwide toward the same objective, and undertaking joint or coordinated action, where possible. 

PS25 marks the eleventh exercise in the enduring APER schedule, following previous successful APER exercises: Australia’s Exercise Pacific Protector 2024 and 2017, the Republic of Korea’s Exercise Eastern Endeavor 2023 and 2019, the United States’ Exercise Fortune Guard 2022 and 2014, Singapore’s Exercise Deep Sabre 2021 and 2016, Japan’s Exercise Pacific Shield 2018, and New Zealand’s Exercise Maru 2015. At the conclusion of Pacific Shield 25, New Zealand announced it will host Exercise Maru 2026.