Eighty years ago this month, the June 1942 issue of Radio Craft showed this walking airplane detector, then under development for use by the Aircraft Warning Service. The headset contained a parabolic microphone and headphones. When the operator heard the low-pitch rumbling of a plane, he could turn his body for the loudest sound, at which point he could look for the approaching aircraft with his binoculars.

The batteries and amplifier were contained in a case “smaller than the usual gas mask container.”