At the onset of the Civil War, he was promoted to
major of the 2nd United States Artillery and was assigned to
Fort Jefferson at
Dry Tortugas, Florida, in January 1861, leaving his command at Fort Independence, Massachusetts. In October 1861, he helped repulse a
Confederate attack on
Santa Rosa Island, and defiantly refused to surrender the outpost during three different Confederate
artillery bombardments. He remained there until May 1862, having rendered invaluable service in defending the fort, which remained in Union hands through the war. In January 1862, he was promoted to brigadier general, and in October 1862 was transferred to command the
city of New Orleans after it fell to Union forces. On November 10 of that year, he was struck down by a stroke while reviewing troops, and was placed on sick leave for over a year while army officials hoped his condition would improve. When it became obvious he would be permanently disabled, he was retired from the Army in February 1864. Arnold died 8 years later in
Boston, Massachusetts and is buried in
St. Mary's Episcopal Church Cemetery in
Newton Lower Falls. ==See also==