BIPSS Research Fellow Alice Daversin explores the growing but often overlooked sub-surface competition in the Bay of Bengal and the Andaman Sea, arguing that the region is evolving into a strategic “Undersea Corridor” linking the Indian and Pacific Oceans. The study highlights how expanding submarine capabilities, hydro-oceanographic mapping, and acoustic intelligence gathering are reshaping regional security dynamics. It warns that the absence of transparency and confidence-building mechanisms risks transforming defensive modernization into an unmanaged arms race. The paper calls for stronger multilateral cooperation to prevent accidental escalation and preserve strategic stability in one of the world’s most vital maritime corridors.