The seabed carries the cables, pipelines and connections that allied economies and defence depend on, yet much of it sits exposed in international waters beyond the reach of any single authority. This session examines the practical challenges of protecting critical undersea infrastructure: the difficulty of monitoring vast and remote areas, the vulnerability of assets to sabotage and accidental damage, and the absence of clear accountability across allied nations, defence and civil industry. It considers what more effective detection, deterrence and shared ownership would require to keep allied CUI secure.