Submarine cables carry about 97% of global communications,
underpin Southeast Asia’s digital economy, and have become increasingly
contested. Yet, they remain under-theorized. Against this backdrop, this
article examines how Southeast Asian states exercise agency over submarine
cable infrastructure amid US-China technological rivalry. Through comparative
analysis of Singapore, Vietnam, and Indonesia, and drawing on semi-structured
interviews, official documents and secondary sources, we find that variations
in institutional capacity, geographic position, and security vulnerability
produce three distinct agency types. Singapore's high capacity, hub position,
and low vulnerability enable "coordinating agency," leveraging
technical excellence and network centrality to influence infrastructure
outcomes while preserving neutrality. Vietnam's moderate capacity, frontier
position, and high vulnerability drive "adaptive agency," steering
infrastructure outcomes through pragmatic adjustments to evolving geopolitical
contingencies. Indonesia's fragmented institutions, chokepoint position, and
moderate vulnerability facilitate "gatekeeping agency," shaping
infrastructure outcomes through strict control over access and complex approval
processes. These findings extend theories of secondary state agency by
demonstrating how Southeast Asian states make use of regulatory and
institutional frameworks to balance pressures from great powers and maintain
autonomy in undersea cable governance. Identifying these trajectories offers
insights into regional connectivity, digital sovereignty, and the dynamics of
techno-geopolitical competition.