''There is no way that submarines, either nuclear or diesel, can...

''There is no way that submarines, either nuclear or diesel, can protect our coasts or our ports. ''

then, submarines are of no use to Australia ---------- end of story

Australia cannot have enough firepower to attack wouldbe enemy- Australia cannot have enough firepower to defend convoys or similar.

Australia cannot have surveillance via submarines to make worthwhile impact compared to our allies

so, if they can't also protect the coastline - then, they are a waste of money ---------

far better to spend a trillion plus on different forms of security or defence