After the American Civil War, the lower battery was redesigned to mount 10-inch Rodman guns. It was a sub-post of Fort Trumbull for most of its use by the Army, although it was never actively garrisoned after the Civil War and had an ordnance sergeant as caretaker. It was in the care of Ordnance Sergeant Mark Wentworth Smith from 1863 to 1879, a Mexican–American War veteran who was wounded at the Battle of Chapultepec. Sergeant Smith died in 1879 at age 76, the oldest active duty enlisted soldier in the history of the Army. Fort Griswold became obsolete after the Spanish–American War, when Fort H. G. Wright was completed in 1906 on Fishers Island as part of the Harbor Defenses of Long Island Sound.