Ironclads like the USS Cairo came equipped with 13 heavy cannon, and each gun required a crew of six men to position and fire it. Operating on the rivers north of Vicksburg, Cairo used its cannon to pound Confederate forts, battle enemy gunboats, and sink shipments of supplies headed to Confederate armies. Interlocking iron plates protected the pilothouse and sloping casemates from enemy fire, and behind the 2-1/2 inch thick plates, white oak planks 12 to 25 inches thick prevented the iron from shattering when hit. Cairo's crew also added iron railroad rails to protect the boat's exposed forward casemate.
