 When a submarine was detected by the guard loop, the operator would wait until there was also a galvanometer "swing" on the mine loop and then the mines would be detonated by sending a current down the mine loop.RAN Station 9 was designed to detect any Japanese submarines or surface vessels attempting to navigate up the Brisbane River.By 1942, the navy had become aware of recent developments by Japan, Germany and Italy in the manufacture and use of miniature submarines and human torpedoes.