This paper examines the drivers and implications of naval build-ups in the Indo-Pacific, considering key actors’ security objectives and threat perceptions, as well as the interplay of regional dynamics and strategic relations between nuclear-armed states. The focus is on undersea armament involving submarines and anti-submarine warfare (ASW) capabilities, which constitute a significant focus of military investments. The paper considers the related horizontal and vertical escalation risks, meaning a potential increase in the scope and scale of conflict.