Wonderful Photos From the Archives A two-horn listening device in use at Bolling Field in Washington, D.C., in 1921, used to detect distant aircraft before the advent of radar. Previous Next Pages: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 2018-03-10 spiel