 During the war, Erwin served in the Confederate Army, rising to the rank of Colonel and commanding of the 6th Missouri Infantry Regiment.In 1863 Josephine Erwin brought the couple's nine-year-old daughter, Lucretia (Lula), to join Andrew Erwin who was part of the force defending Vicksburg.Andrew Erwin was killed in the Battle of Vicksburg, one week before the end of the Union siege.