Morgan Michaels, Daniel Salisbury, Evan A. Laksmana
This research paper reports on the insights and lessons learned from an IISS-organised two-day diplomatic crisis-simulation exercise held in Singapore on 24 and 25 November 2025. The exercise brought together 30 participants from Indonesia, Malaysia, the Philippines, Singapore, Thailand and Vietnam, comprising leading experts as well as government and security officials all attending in their private capacity. IISS experts also participated as ‘control teams’ playing the role of Australia, China, the United Kingdom and the United States.
The exercise centred on a hypothetical scenario involving a missing nuclear-armed submarine in Indonesian waters in 2031 and how it sparked broader military tensions between China and the Australia–UK–US (AUKUS) partnership. The exercise was designed to stress test how key Southeast Asian states could leverage the ASEAN Defence Ministers’ Meeting (ADMM) and ASEAN Defence Ministers’ Meeting Plus (ADMM-Plus) as a conflict-prevention and crisis-response mechanism.
As the submarine disaster occurred in Indonesian waters, the other Southeast Asian teams largely deferred to Indonesia to manage the crisis, while expressing support through and for the ADMM. Their focus tended to be on areas of particular national concern or where they believed they could contribute most effectively. A recurring theme throughout the simulation was the issue of strategic bandwidth, and the limited diplomatic capacity of ASEAN member states (AMS) to respond to a major nuclear-security crisis.