During the Spanish–American War in 1898, Smedberg served as aide-de-camp to Brigadier General Samuel Baldwin Marks Young, who commanded one of two brigades that made up the Cavalry division commanded by Joseph Wheeler. He took part in the Battle of Las Guasimas and Battle of San Juan Hill, and was officially commended by Leonard Wood, the commander of the 1st U.S. Volunteer Cavalry Regiment ("Rough Riders"), which was part of Young's command. Smedberg received the Citation Star to recognize his wartime heroism. When the Silver Star was created in 1932, Smedberg's decoration was converted to the new medal.