 The nine @-@ inch gun was credited with the ability to penetrate 11 @.@ 3 inches ( 287 mm ) of wrought iron armour at the muzzle . The eight @-@ inch gun could penetrate 9 @.@ 6 @-@ inch ( 244 mm ) of armour and the seven @-@ inch gun could penetrate 7 @.@ 7 inches ( 196 mm ) . 
