How about the South Korean military? Don't you think they have ASW assets? And in the region, too?
I would hope that every available P-8 and P-3 is on patrol, seeding the Yellow Sea and Sea of Japan with sonabouys. Between the U.S., ROK and Japan, we should have enough patrol craft and vessels to begin tracking down some of those noisy NK boats. Unfortunately, Zero never wants to take the lead on any sort of military operation, and it takes U.S. leadership to get the ROKs and Japanese to cooperate.