Well, USN likes to say that best weapon against a submarine is another submarine. But basically, only real weapon is good sonar/antisub torpedo combination. Helicopters seem to be asw platforms of choice for surface fleets. They have sonars that they lower/dip into water, track for subs, can quickly change position (compared to surface fleet/other subs) and then launch torpedoes. Whereas using an active sonar on a surface ship/sub would pretty much give away the position of it from miles away, endangering the ship/sub, helos can go out of ships trajectories/miles in advance of the mother ship and actively seek subs without fear of being engaged by sub or giving endangering their mother ship.
As for why china doesnt seem to be pushing asw capabilities... i guess they dont think conflict with USN is likely. And that's pretty much only enemy where strong asw would be needed. All the other neighbours and especially taiwan as most likely enemy, have much weaker sub forces.
As for why china doesnt seem to be pushing asw capabilities... i guess they dont think conflict with USN is likely. And that's pretty much only enemy where strong asw would be needed. All the other neighbours and especially taiwan as most likely enemy, have much weaker sub forces.