To clarify EM waves which are used for most(all?) tracking in the atmosphere, are attenuated very quickly in water. Underwater sound waves work better. I don't

To clarify EM waves which are used for most(all?) tracking in the atmosphere, are attenuated very quickly in water. Underwater sound waves work better. I don't know what this submarine used but I would expect at minimum an acoustic transponder to aid in underwater tracking. with a acoustic telephone as a comm channel. However reading about some of their other engineering decisions this is probably too optimistic of me. Data recorders(airplane black boxes) have a sound pinging unit for this exact case. being lost under water.