Sgt. Gray operating a longwave receiving set at the Signal Corps field laboratory in March 1919. The device had a range of 6000 to 18000 meters and was used for military communication purposes. Unauthorized publication of this image is prohibited.

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Keywords: .., 6000, 18000, activities, american, corps, field, gray, laboratory, long, meters, military, official, photo, publication, range, receiving, set, sgt., signal, war, washington, wave, world