 The turret faces were 11 inches ( 279 mm ) thick while their sides were 6 inches ( 152 mm ) in thickness , and the roof was five inches thick . The barbettes had a maximum of 9 inches ( 229 mm ) of armor , but were reduced in thickness in stages below decks to a minimum thickness of five inches . The conning tower armor was 12 inches ( 305 mm ) thick , and it had a communications tube with 10 inches ( 254 mm ) sides ran from the conning tower down to the lower conning position on the 1st platform deck . The torpedo defense system of the Lexington @-@ class ships consisted of three to six medium steel protective bulkheads that ranged from .375 to .75 inches ( 10 to 19 mm ) in thickness . The spaces between them could be left empty or used as fuel tanks to absorb the detonation of a torpedo 's warhead . 
