[2] There were three sets of fortifications built in Mosman and Middle Head in the 1870s, these were upgraded in the 1880s on the advice of British experts.

The whole area is linked by an extensive network of tunnels, ancillary rooms, gunpowder magazine and a disappearing gun emplacement.

Rooms located below ground were used to train some of Australia's first troops who were sent to Vietnam in 'Code of Conduct' courses, which were lessons in how to withstand torture and interrogation, by simulating prisoner of war conditions.

The army base on site which included the transport group and 30 Terminal Squadron, left Georges Height's in 1997.

During World War II this building served as a Red Cross Hospital and later as accommodation for the Australian Women's Army Service.

The sites facilities include: Middle Head Military Fortifications was listed on the New South Wales State Heritage Register on 2 April 1999[1] and in 2004 the Chowder Bay Barracks Group, including the Georges Head Battery, was inscribed on the Commonwealth Heritage List.

[6] This Wikipedia article contains material from Middle Head Military Fortifications, entry number 00999 in the New South Wales State Heritage Register published by the State of New South Wales (Department of Planning and Environment) 2018 under CC-BY 4.0 licence, accessed on 2 June 2018.