Methods of detecting submarines have been many and varied but one which rose to prominence in World War Two 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 Thomas Faraday in the 1800s but developments by the British Admiralty before and during the Second World War saw it reach its zenith and then disappear almost as soon as the war finished. 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 its development 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. Comment is made on how social needs drove the science and technology behind this anti-submarine technology.