Methods of detecting submarines have been many and varied, but one which rose to prominence in World War II was based on sensing the magnetic field of a vessel as it passed over conducting cables laid on the seabed. Such 'indicator loop' technology was founded on the work of the scientist. Michael Faraday, in the 1800s but developments by the British Admiralty before and during World War II saw it reach its zenith and then disappear almost as soon as the war finished. The devices -known as indicator loops -have been classified as secret all of their working life and only a small number of men and women knew of their existence. This article surveys the history of the development of indicator loop technology particularly as an outgrowth of controlled mining, and focuses on the Royal Australian Navy's Operation 'Robert and Arthur' in Moreton Bay as a case study in its deployment. An examination is made of the different backgrounds of several men and how this may have shaped their personalities before coming together for two years at Bribie Island. Consideration is also given to how social needs drove the science and technology behind this form of anti-submarine defence.