Irvin McDowell
After the end of the Civil War, Gardiner was commissioned a second lieutenant of the 9th Infantry Regiment of the Regular Army, to rank from July 20, 1866, and was promoted to first lieutenant on February 14, 1868. He transferred to the 1st Artillery Regiment on April 3, 1869, and served for a time as aide-de-camp to Major General Irvin McDowell who was commander of the Department of the East with its headquarters on Governors Island in New York Harbor.