ation of the island was seen as being important to the defence of the important port of Fremantle, the major base for the Allies in the Indian Ocean, as bombardment of any attacking ships could be made from the island before the ships would come into range of the port.
A light railway was built from the jetty at Kingstown Barracks on Thomson Bay, to transport materiel and munitions to the guns. The military fixtures including the barracks and railway became known as the "Rottnest Island Fortress". A number of concrete lookouts and bunkers were built around the island also.
Near Wadjemup Lighthouse, a Battery Observation Post (BOP) was built as a lookout to coordinate aiming and firings from the Bickley and Oliver's Hill Batteries. A Signals Building, associated with the BOP and a Women's Army Barracks, built to house officers and staff who operated the BOP were constructed there also. The latter building is used nowadays for occasional accommodation for University and other scientific research groups working on the island.
After World War II the guns and infrastructure were decommissioned and parts of the railway removed. The 9.2-inch battery, however, was saved from disposal because the high cost of removing and shipping the guns to the mainland exceeded their value as scrap metal.
In the 1990s the gun emplacements and railway were extensively reconstructed and today a popular tourist activity includes tours over the guns and the tunnels with the journey to the battery being made on a purpose-built train.
Communications
Prior to about 1880, communication with the mainland was primarily with semaphore flags and flares. A manned lookout at Bathurst Point included a signalling station which relayed shipping information between Wadjemup Lighthouse at the centre of the island and Arthur Head at Fremantle.
A heliograph was installed in 1879 at Signal Hill, the small rise overlooking the main settlement in Thomson
