America entered World War One almost totally unprepared. Her most urgent problem was the training of at least one million men. This thesis describes the content of tactical training in the United States Army, the development of an efficient system for producing qualified replacements for combat units, and the theoretical differences between Allies, American Expeditionary Forces and authorities at home. Because cavalry was employed on only the most minimal scale during the First World War, no attention has been paid to training for "l'arme blanche." Supporting forces such as aircraft, engineers or signals have been left out of this discussion in order to save space. An analysis of American tactical doctrine concludes this work. Ideas concerning methods of assaulting machine guns are the author's own, for which full responsibility is accepted. Because the war ended before the full weight of America's military force could be applied, analysis of her performance on the battlefield must be tempered with an awareness that the final sophistication of her training system occurred too late to be of assistance to Pershing's army. The excellence of tactical education as it evolved in World War One would remain unproven until America entered a vaster and more desperate struggle twenty-four years later.