Military historians have been debating the U.S. Army's World War II replacement system for decades, but no one has completed a detailed study of the War Department's policies and practice. Authors have focused primarily on how combat units overcame the system's limitations, but they have not conducted an in-depth examination of its creation, structure, and function. Nor did they question why infantry divisions had to devise their own replacement policies in the first place. The extant literature is too celebratory of the army and utilizes ultimate victory as a measure of efficiency and effectiveness. Such a myopic view has prevented these earlier studies from evaluating how the replacement system affected the overall course of the European war. This dissertation breaks new ground by presenting a comprehensive overview of the replacement system--from the War Department down to the squad, and from the last days of World War I through the post-World War II years. It will elucidate a process of failed administration and implementation at the highest levels of the War Department and army, but it will also relate a "grassroots" story of success at the divisional level and below. The War Department's managerial approach to the utilization of military manpower was both inefficient and wasteful. The army largely overlooked the impact of individuality, morale, psyche, experience, and training on a soldier's performance. Its insistence on rushing men to the line once combat operations began meant that it often neglected to train, orient, and equip replacements in a manner conducive to their favorable and effective integration into combat units. The GIs at the front, both veterans and replacements alike, suffered for this oversight. / History