The more mobile an armed force becomes, the more rugged the terrain it encounters, or the more widely the force is deployed, the greater becomes the difficulty of securing and maintaining rapid, completely linked communications. In the U.S. Army the Signal Corps is the agency charged with developing, procuring, and furnishing signal equipment to overcome the difficulties mentioned above. In an age of swift and startling progress in electronics, this phase of its mission demands that it keep abreast of scientific advances at home and abroad and maintain close ties with civilian laboratories and industry in order to take advantage of their capabilities. This volume traces the course which the Signal Corps followed between the first and second world wars, a period of planning and preparation. Others to follow will recount the testing of the Corps' organization and equipment, and the results achieved at home and overseas. The author has dealt with the subject on a chronological basis, instead of following the topical treatment used in other technical service volumes. This broad-front approach has enabled him to weave into one pattern the many activities in which the Signal Corps was simultaneously engaged. The reader can here follow from birth the history of Army radar and mobile radio, the first steps taken in the conversion of the civilian communications industry to war production, the expansion of training facilities, and the beginnings of the far-flung communications network that eventually encircled the globe. He will see the uncertainties of planning and the difficulties of organization incident to rapidly changing conditions, meager appropriations, and the clash of interest within the military household. These and many other matters showing human beings and institutions under pressure are replete with significance to us who must live in a turbulent world where revolution tends to have the upper hand over evolution.