 Discharged as chief trumpeter at the expiration of a three-year enlistment, he remained a civilian for about one and a half years and then reenlisted in the Army on April 28, 1904.He was honorably discharged by purchase on November 12, 1905, as a chief trumpeter with the First Band, Artillery Corps.Ostermann accepted a second lieutenant's commission in the Marine Corps on March 20, 1907, and served continuously until his retirement as a major general on January 1, 1943.