30 Rare Historical Photos You’ve Probably Never Seen Or Will Ever Find In Image Stocks
Sound Finders
These strange horn looking machines called “sound finders” were used to alert the sounds of distant aircraft engines. Used as Soviet Plane-spotters around 1917.It was the only form of early warning against aircraft before the invention of radar in WWII.
30 Rare Historical Photos You’ve Probably Never Seen Or Will Ever Find In Image Stocks
