Sound is still useful
Counter Bombardment and Counter Mortar Battery Equipment. Is still in use today to pinpoint enemy mortar fire locations.
No doubt based on these concrete structures but using modern microphones and computers.
Nice link here for modern adaptations...
https://en.m.wikipedia.org/wiki/Artillery_sound_ranging
Very nice article, next to BOHF these keep me coming back.
Biting the hand that feeds IT
