Anti-submarine indicator loop

Balfour appreciated the importance of science, so he established a Board of Invention and Research (BIR), composed of a three-man central committee supported by an eminent consulting panel.

[5] He had shown that the passage of a submarine past a cable formed an induction loop which induced a voltage of approximately a millivolt, detectable by a sensitive galvanometer.

Voltages were also induced in the cable by random fluctuations in the Earth's magnetic field and electrical noise from the Glasgow tram lines.

[9] The German submarine UB-116, captained by Lieutenant J J Emsmann, who, along with his crew had volunteered for a suicide mission, was detected by hydrophones at 21:21 on 28 October 1918 while entering the harbour via Hoxa Sound.

Two hours later, at 23:32, current was detected in an indicator loop laid in a remotely controlled minefield, induced by the submarine as it passed over the cable.

[14] An indicator loop gave the first warning of the 1942 attack on Sydney Harbour, when it detected the midget submarine M-14, but that signal was ignored, owing to civilian traffic in the area.