American soldiers used the scale and scope of their needs for leisure and recreation during World War I to push army officers and welfare secretaries to reshape the production, distribution, and consumption patterns constituting mass culture. By observing these developments, this dissertation improves our understanding of the social history of the military and the history of American capitalism. Mass conscription of four million recruits created an unprecedented army marked by the racial, ethnic, and class diversity. Progressive administrators from seven welfare organizations and the War Department organized entertainment and morale programs on their behalf, but also reaffirmed segregation and racism. Going beyond interpretations of wartime welfare as an effort to remake young men or replicate middle-class lifestyles, I borrow from and contribute to business and consumer history to illustrate individuals’ ability to reshape institutions. Utilizing diaries, letters, memoirs, correspondence, plans, and records from soldiers, officers, welfare organizations, and corporations, collected from forty-five archives in nineteen states and Washington, DC, I demonstrate how welfare officials recruited experts from Sears, Standard Oil, the Keith vaudeville circuit, and other companies to modernize factories, improve shipping networks, and popularize new consumer goods. As the American Library Association, Commission on Training Camp Activities, and YMCA structured informal leisure activities like reading, singing, and dancing, they also embraced business and management techniques to study troops’ interests and circulate feedback. Chautauqua tents, Liberty Theatres (formed by Marc Klaw of the Theatrical Syndicate), and Play Factories run by the Services of Supply provided content, infrastructure, and logistics for professional and soldier stage shows. As troops’ demanded more mechanized entertainments including phonographs and movie projectors, welfare workers adopted new technologies to expand their exhibition capacities. CTCA officials studied conscripts’ preferences to teach sports like boxing and discover their favorite baseball gear, and gradually accepted spectator sports that troops and Knights of Columbus coaches and trainers had initially promoted. Servicemen even bought mass-produced cigarettes, chocolates, razors, and cameras from army post exchanges and welfare canteens that protected consumers from price gouging. In every instance, “soldier-consumers” pressured welfare administrators to restructure welfare programs according to troops’ needs and shaped mass culture.