This document gives historical background on water transportation for the United States Army. The purpose of this study is to trace the organization and activities relating to water transportation for the U.S. Army prior to the reorganization of the War Department in March 1942. The major emphasis will be placed upon the period after July 1, 1940. There is information on the expansion of the Water Transport Branch, 1939-42, the Army Transport Service, Army ports of embarkation, harbor boat service, effect of American entry into the war, and a review of accomplishments (1939-42).