In order to service Royal Navy ships, the Fitzroy Dock was built on the island and completed in 1857.

The New South Wales Public Works Department declared Cockatoo the state dockyard.

[1] After Federation, in 1913 Cockatoo became the Commonwealth Dockyard, and the island, both through shipbuilding and servicing, played an important role both in the development of the Royal Australian Navy and during the First World War.

From 1933 the dockyard was leased from the Australian Government by Cockatoo Docks and Engineering Co Ltd and the island played a very significant role during the Second World War.

It was designed by the Commanding Royal Engineer Colonel George Barney, who played a notable role in the colony.

Various extensions were added (a latrine and office block formed infill when built later).

[1] The barracks is a single storey sandstone building, built in a rare U-shape, and with an enclosed court.

[1] Criterion H: Significant people The block was designed by Colonel George Barney, who as Commanding Royal Engineer played a notable role in the colony.

[1] This Wikipedia article was originally based on Barracks Block, entry number 105257 in the Australian Heritage Database published by the Commonwealth of Australia 2018 under CC-BY 4.0 licence, accessed on 17 September 2018.