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 ship-building 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.

During the period of the girls school, the residence was occupied by the new registrar of the Sydney water police who stayed until 1896.

With the Commonwealth takeover in 1913, the northern quarters became the shipyard manager's home and the southern became offices.

[1] Clerk of Petty Sessions Cottage was built prior to 1845 and was also designed by the Commanding Royal Engineer.

[1] The main buildings in the group, along with the Prison Barracks Precinct, form the only imperial-funded (as opposed to colonial-funded) convict public works complex in NSW.

[1] Due to the uncertain grain supplies available in the early colony of NSW, Governor Gipps in 1839 decided to embark on a program of silo construction on the Island.

Gipps hoped to increase storage up to 100,000 bushels if the low price of wheat then prevailing continued.

The other major group of convict constructed underground silos are located on Norfolk Island, these are cut into the earth.

The Clerk of Petty Sessions Cottage was in very good condition and had been recently re-painted and re-roofed.

[1] Criterion A: Processes Constructed mainly in the early 1840s, the elements of the Biloela Group are historically highly significant for their direct association with convict administration in the Australian colonies.

[1] Criterion B: Rarity The group, along with the separately registered prison barracks precinct, is the only remaining imperially funded convict public works complex in NSW.

[1] Criterion D: Characteristic values The group, along with the separately registered prison barracks precinct, is the only remaining imperially funded convict public works complex in NSW.

[1] Criterion F: Technical achievement The silos are finely excavated and reflect a high degree of stonemasonry skills on the part of their builders.