"Nereus" played no role in the Battle of Sydney Harbour (often referred to as the Attack on Sydney Harbour) and her whereabouts at the time has not been established.  However, Muirhead-Gould’s (commander of Sydney Harbour) 22 June Report, includes that on the night after the Battle, "Nereus" attacked and claimed to have sunk a submarine in Vaucluse Bay.  At the time of his report, Muirhead-Gould believed the claim was genuine, but later considered the report to be a false sighting.