Fremantle Fortress 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.