French navy using microphones as defence against approaching torpedo boats according to the Dutch magazine Marineblad dated 1905-1906 no. 10

An item referred to the magazine Marine Rundschau reporting that a naval officer invented microphones which were able to pick up over a distance of 5 sea miles approaching torpedo boats. It was even to possible to recognize the turning of the screws. For the defence of Cherbourg, France were before the harbour entrance 12 of these microphones anchored.