 In February, 1862, shortly after occupying the stone house, Amos enlisted as a private in Company E, 5th Infantry Regiment Minnesota.He was promoted to the ranks of Sergeant (April 2, 1862), 1st Lieutenant (August 2, 1863) and Full Captain (February 9, 1865), before mustering out at Fort Snelling on September 6, 1865.As a member of the 5th Minnesota, Amos participated in the Siege of Corinth, Mississippi (May 26–30, 1862); the Battle of Corinth (October 3–4, 1862); Grant’s central Mississippi campaign (November 1862-January, 1863); the Siege of Vicksburg (May 18-July 4, 1863); and the Battle of Nashville (December 15–16, 1864), among numerous other campaigns.