In 2008 and again in 2011 there were clusters of incidents involving undersea cables that led to disruption.
I can’t imagine a single ship being able to effectively monitor undersea cables.
But I can imagine a mothership deploying semi-autonomous persistent drones and sensors to detect and someday possibly even disrupt/destroy threats to the cables.
A simple CARVER matrix says the cables are far harder to defend than attack.
However, the potential attackers are limited to a very small number of sovereign states with the capability to detect/disrupt cable traffic and a larger but still small number of sovereign states with the capability of destroying cable traffic.