uth-west to a point just west of Adelaide, as recounted by Warwick Outram in Bribie Memories 2nd edition 2009 ISBN 978-0-9751971-4-1. George H. Johnston, War Correspondent for the Argus newspaper was present when MacArthur mentioned the Brisbane Line on 16 March 1943, but later clarified the matter by writing It was Gen. MacArthur who abandoned the Brisbane Line concept and decided that the battle for Australia should be fought in New Guinea.
At Fort Bribie itself, two mine control huts were used by Royal Australian Navy during 1942 and 1943, known as RAN 2. These monitored and controlled the guard indicator loops and mine loops set in the North West Channel. The indicator loops relied on a moving magnet or any large mass of metal, which naturally acquires magnetic force, to induce a current in a stationary loop of wire. If a submarine was detected by the guard loop, the operator would wait until there was also a swing mine loop before detonating the mines by sending a current down the mine loop. RAN 2 was moved to Cowan Cowan on Moreton Island in September 1943. When the mines in Moreton Bay were decommission at the end of the war, six were missing. One was found at Tewantin in 1945.
The mines weighed 1430 kg and were buoyant, so needed to be moored with sinkers, up to 25 metres below the surface. Every 5 minutes hour perturbations due to the tides known as perts had to be recorded. Daily and weekly tests were carried out on all equipment. In three years of operation, the mines were never detonated.
Another minefield with guard loop built in 1942 protected Pearl Channel and Main Channel south of Bribie Island. The guard loops ran from the Loop Control Hut at the end of North Street, just north of Woorim to Combouyuro Point, Moreton Island. Three Harbour Defence Asdics, sea-bed mounted submarine detection devices now known as sonar, were position down-channel from the guard loops, as a second means of detection
