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Research involved in the development of a radio communication system for use in coal mine disasters is described. Theoretically predicted field strengths for surface to mine and mine to surface propagation are compared with measurements in coal mines in Colorado and Pennsylvania. It is concluded that surface-to-mine voice communication is practical using a horizontal wire antenna operating at audio frequencies, and that mine-to-surface interrupted CW signaling is practical using multiple-turn horizontal loop antennas. This research has resulted in an emergency through-the-earth communication system that is being evaluated by the U.S. Bureau of Mines for use in mine rescue operations.