Private Robert McArthur (center) and two comrades of the U.S. Army pose for a formal portrait at J.C. Spooner's Picture Palace, Foots Block, corner Main & State Streets, Springfield, Mass.

McArthur enlisted at Springfield, Massachusetts, and was mustered February 10, 1864. He was in Company I, 3rd Regiment of the Massachusetts Heavy Artillery Volunteers.

He was discharged at the end of the war in 1865. McArthur was for many years the agent of the Pepperell Mills in Biddeford, and the most prominent man of his time.