Practical communication by radio telephone is a comparatively recent development. Although successful experiments with the radio telephone extend back through a period of years it was not until the entry of the United States into the war that the radio telephone was put to practical use for comunication on any considerable scale. Even then, it was used with small, low-power apparatus intended primarily for communication between sub-chasers and similar small craft. The later developments in radio telephony, including the application of greater power, and hence the attainment of greater range, were rendered practicable largely through the development of vacuum tubes, which development was intended primarily for the improvement of radio telegraphic communication.
Some Phases of Radio Telephone Broadcasting
By Lieutenant A. H. Tawresey, U. S. Navy