Many Union wooden warships had, at one time or another, chains drapped over their sides as an improvised "armor". Most "ironclad" ships were just that, clad. Even USS Monitor was basicaly an ironcovered wooden raft. The monitor turrets, however, were all iron armor. The Monitor's turret was 8in thick. Later monitors were much thicker. No monitor turret was ever penetrated by Confederate gunfire. On the other side, the base Confederate armor protection was 4in, with a backing od about 24in of wood. When CSS Atlanta was captured after a 20min engagement with a Union Monitor (whose 15in Dahlgren opened up the ships casemate) the CS Navy increased the thickness on their next ironclads (they commisioned 22 in all) to 6in and with the last ships, to 8in. It did no good. The 15in sb was capable of penetrating all. The most "formidable" Union naval vessel was probably USS New Ironsides. She was armed with 14 11in SBs and 2 150lb rifles. Her armor was about 4and a half inches with 22inches backing of wood.