How different is that from the US Coast Guard's (and especially regular merchant ships whose crews are part of the Coast Guard Reserve's) wartime function? I would suppose that all organized merchant-marine escort fleets are trained to cooperate/coordinate with their country's Navy; if not just to "get the heck out of the way, this area is about to be under attack."

Also, AFAIK, it's a de-facto "law of the sea" that pretty much all ships with transponders—no matter the flag they fly—will willingly act as relays for other ships that cannot communicate, in order to facilitate search-and-rescue. Same with planes. It's a whole part of their signalling codes.