Before the invention of radar, you'd need a large dish or
horn to track sounds of your enemy. "Acoustic radar" (aka "acoustic
locators" or "sound mirrors") captured sound via large dishes or walls,
or steerable horns not unlike the cones on early record players.
Douglas Self has a reference guide to this curious technology with links as part of his Museum of Retro Technology. (via near near future) Check out the fluidic gramophones, too!
I know what you're thinking: could you sample the sounds captured by
such a dish? I leave it up to our UK readers to head over to the ruins
of some of these things to try it out. Let us know.