The matter of transportation at home and abroad becomes one of first importance when war strikes. The strain on the transportation systems and the conflict of civilian and military demands become immediate and serious problems. In two world wars the United States has had to solve many of these problems after hostilities began, and therefore to solve them in haste, by trial and error. As new and improved means of transport are introduced, the questions of military transportation become more difficult. The horse and mule had their shortcomings, but their use involved few of the complications that bedevil the military in this machine age. The armed forces must have not only adequate equipment but also replacement parts to keep that equipment operating in the field. Efficient use of transportation necessitates co-ordination within the armed forces and between military and civilian agencies. During World War II much was done to increase effective use of ships, railway cars, and motor vehicles, but efforts to balance the competitive demands of civilian and military traffic in the zone of interior were only partially successful. Careful planning is necessary to reduce difficulties such as those which beset us in 1917 and 1941. The present volume, first of this series to deal with the Army's technical services, begins an account of the transportation problems of the Army and their solution in World War II, including those of inter-Allied co-ordination. This volume is the first of three concerning the Army Transportation Corps in World War II. It delineates the nature of the transportation task, the functions and organization of the Transportation Corps, and its operating problems and relationships in the zone of interior. A second volume will deal with the execution of troop and supply movements in the zone of interior and to the oversea commands, the organization and training of Transportation Corps troops, and the development, procurement, and distribution of Transportation Corps mat�riel. A third volume will describe Transportation Corps organization and activities in oversea theaters and bases. Between the covers of this book is to be found information that will contribute substantially to our planning and preparation for transportation emergencies in the future.