This report examines Australia–India anti-submarine warfare (ASW) cooperation within an increasingly contested Indo-Pacific undersea environment. It argues that meaningful, campaign-level cooperation is both achievable and strategically valuable without requiring alliance-style integration or the sharing of highly sensitive sensor architectures.  Cooperation is best structured around aligned doctrine, greater intelligence sharing, and routine operational coordination that builds the enduring relationships between the two operational-level headquarters.

Rather than pursuing technically ambitious but politically unsustainable integration, particularly in areas such as acoustic libraries, seabed sensor data, or strategic deterrent intelligence, Australia and India should prioritise doctrinal alignment, decision-grade information sharing, and mechanisms for sustained, operational coordination. These measures are sufficient to generate improved awareness of submarine activity, disrupt adversary operations, and strengthen deterrence by denial.

China’s expanding submarine fleet and its growing operational reach into the Indian Ocean Region (IOR) represent the central pacing challenge. As the PLA-N extends its operational footprint, it also exposes itself to cumulative vulnerabilities across long transit routes, unfamiliar acoustic environments, and extended logistics chains. Australia-India cooperation can exploit these vulnerabilities not through direct confrontation, but through persistence, attribution, and uncertainty under a strategy of deterrence by denial.

This report argues for a shift from operational-level coordination being based on planned exercises to enduring ‘real-world’ operational cooperation, supported by institutionalised relationships and greater operational coordination.