Sydney Harbour, between Bradleys Head and Clark Island. 19 November 2017
Looks like a family day with civilians on board.
Vessel near 33°51'30.67" S 151°14'28.87" E

See RAN web site http://www.navy.gov.au/hmas-darwin
HMAS Darwin is a long-range escort frigate that undertakes roles including area air defence, anti-submarine warfare, surveillance, reconnaissance and interdiction. The ship is capable of countering simultaneous threats from the air, surface and sub-surface.

Darwin and her five sister frigates HMA Ships Adelaide, Canberra, Sydney, Melbourne and Newcastle were the first Royal Australian Navy ships to be powered by gas turbines for its main propulsion.