Sanno served with the 7th Infantry as part of the Union Army during the American Civil War. Shortly after the July 1863 Battle of Gettysburg, the 7th Infantry was ordered to New York City to take part in the response to the draft riots. Sanno was promoted to first lieutenant in December 1863. The regiment remained in the city through the end of the war in May 1865, then deployed to Florida for post-war occupation duty during the Reconstruction era.