Explain for me, if you will, the physics that allows sound to reach a submarine under several layers yet the sound it produces can't be detected? After you've done that, pse explain where, exactly, these "several layers" exist.
Technical question that would need long answers but the short answers are:
Being careful what I say... submarines can tow an array that may be at a different depth to the boat (one bit above and one bit below a layer) and this will assist in detecting who is about, plus once they know who is hunting them it is time to either scoot, shoot or hide.
Final question
Submarines are always monitoring and recording sea temperatures, alkalinity and sea pressure which will enable them to build up a picture of the various layers which in turn will then mask or help mask their presence.
Obviously this is a highly specialised topic and worthy of deeper discussion but suffice it to say the submarine has lots of very specialised equipment that helps it in this game of hide and seek. It is not unknown for submarines to 'disappear' under these layers and then simply scoot away.
To my knowledge a nuclear submarine can outrun a surface ship but so far it cannot out run a helicopter
(humour)