Collins Class ,HMAS FARCOMBE entered the Derwent in the last few days submerged until outside the constitution dock area where it surfaced surprising a lot of Hobart residents.
-----the quietest conventional powered submarine class yet built.
I'm guessing it is probably a an escape training facility where crew are trained to exit a submarine.It could also be the Torrens where the Collins boats were built.or Hmas Platypus in Sydney