Cockatoo Island is the largest of several islands that were originally heavily timbered sandstone knolls. Originally the Island rose to above sea level and was but it has been extended to and is now cleared of most vegetation. Called Wa-rea-mah by the Indigenous Australians who traditionally inhabited the land prior to European settlement, the island may have been used as a fishing base, although physical evidence of Aboriginal heritage has not been found on the island.
Between 1839 and 1869 Cockatoo Island operated as a convict penal establishment, primarily as a place of secondary punishment for convicts who had re-offended in the colonies.
Cockatoo Island was also the site of one of Australia's biggest shipyards, operating between 1857 and 1991. The first of its two dry docks was built by convicts. Listed on the National Heritage List, the island is significant for its demonstration of the characteristics of a long-running dockyard and shipbuilding complex, including evidence of key functions, structures and operational layout. Cockatoo Island contains the nation's most extensive and varied record of shipbuilding, and has the potential to enhance understanding of maritime and heavy industrial processes in Australia from the mid-19th century.