In April 1898, during the Spanish–American War, he enlisted in the Army under the name Thomas E. (Edwin) Mix. His unit never went overseas, and Mix later failed to return for duty after an extended furlough when he married Grace I. Allin on July 18, 1902. Mix was listed as AWOL on November 4, 1902, but was never court-martialed nor apparently even discharged. His marriage to Allin was annulled after one year. In 1905, Mix married Kitty Jewel Perinne, but this marriage also ended within a year. He next married Olive Stokes on January 10, 1909, in Medora, North Dakota. On July 13, 1912, Olive gave birth to their daughter Ruth.