In a hypothetical modern peer war, what is the status in international law about commerce raiding targeting merchant shipping? Would American submarines be allowed to sink cargo vessels leaving or heading toward Chinese ports? Could Ukraine fire anti-shipping missiles or use maritime drones against Russian-flagged oil tankers?

And beyond what the "legal" view is, do we have any indication from publicly available plans about what major players, like China and the US, would do in this environment if a war did happen? Has China said they would sink ships headed to (eg) taiwan or Japan in the case of war? Would the US use its naval power to try and enforce a blockade of China via destroying merchant shipping?