 She was armed with a main battery of four 13 in ( 330 mm ) / 35 caliber guns guns in two twin gun turrets on the centerline , one forward and aft . The secondary battery consisted of fourteen 6 in ( 152 mm ) / 40 caliber Mark IV guns , which were placed in casemates in the hull . For close @-@ range defense against torpedo boats , she carried sixteen 6 @-@ pounder guns mounted in casemates along the side of the hull and six 1 @-@ pounder guns . As was standard for capital ships of the period , Illinois carried four 18 in ( 457 mm ) torpedo tubes in deck mounted launchers . 
