Otto B. Swanson entered the military service in Illinois. He served in the U.S. Army during World War I as a Private in Company D, 28th Infantry Regiment, 1st Infantry Division. He was Killed in Action on July 21, 1918 and is now buried in Meuse-Argonne American Cemetery and Memorial, Romagne-sous-Montfaucon, Departement de la Meuse, Lorraine, France. His remains were originally buried in a shell hole on the battlefield and remained lost until accidentally rediscovered in 1933 and reburied. His name was originally listed on the Tablets of the Missing at the Aisne-Marne American Cemetery near Belleau Wood; that inscription is now marked with a bronze rosette to indicate his remains were found. The story of his unit is told in the book The Remains of Company D by James Carl Nelson.