Fortress Fremantle was the combined coastal defences protecting the harbour of Fremantle, Western Australia, since the mid-1930s and, predominantly, during World War II. The coastal defences of the Fremantle Fortress stretched along the coastline of Perth from Cape Peron to Swanbourne and also included installations on Garden Island and Rottnest Island. While the first coastal batteries of the future Fremantle Fortress were installed at Arthur Head in 1906, the military installations protecting the harbour were expanded in the 1930s, being eventually dismantled again by 1963.
During World War II, Fremantle Harbour, guarded by the Fremantle Fortress, was home to the Fremantle submarine base, which was the second-most important submarine base in the Pacific War after Pearl Harbor.The coastal batteries were manned by members of the Royal Australian Artillery, the Royal Australian Engineers and the Volunteer Defence Corps. Apart from these men, members of the Australian Women's Army Service also served at the Fortress.
The Army command structures of Fortress Fremantle were one part of an all arms defence of Western Australia stretching primarily from geraldton to Albany. Mobile land formations, naval control of shipping, anti-aircraft defences, fighter and patrol aircraft and their early warning and coordination centres all formed part of the World War 2 defence pasture of Western Australia.
