WW2 was an era of innovation and invention as well as a dark moment in history.
One of my all time favorite images is this one:
Sound location equipment in Germany, 1939. It consists of four acoustic horns, a horizontal pair, and a vertical pair, connected by rubber tubes to stethoscope type earphones worn by the two technicians left and right. The stereo earphones enabled one technician to determine the direction and the other the elevation of the aircraft.