Using a two-horn listening device at Bolling Field in Washington, D.C., in 1921 before the invention of radar, to listen for distant aircraft. [1500x1064]
#vintage #Using a two-horn listening device at Bolling Field in Washington, D.C., in 1921 before the invention of radar, to listen for distant aircraft. [1500x1064] #history #HistoryPorn #Bot http://ift.tt/2DFa9e7
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