 The armor of the casemate was angled at 30 ° from the horizontal and made from two layers of railroad rails , rolled into plates 2 inches ( 51 mm ) thick and 7 inches ( 180 mm ) wide . The outer layer ran vertically and the inner layer horizontally . Her armor was backed by 3 inches ( 76 mm ) of oak , vertically oriented , and two layers of 7 @.@ 5 inches ( 191 mm ) of pine , alternating in direction . The bottom of the casemate was some 20 inches ( 508 mm ) from the waterline and its top was 8 feet 6 inches ( 2 @.@ 59 m ) above the waterline . The pyramidal <unk> was armored in the same way and had room for two men . The upper portion of Atlanta 's hull received two inches of armor . 
