 The ship was armed with a main battery of ten BL 13 @.@ 5 @-@ inch Mk V naval guns mounted in five twin gun turrets . They were arranged in two superfiring pairs , one forward and one aft ; the fifth turret was located amidships , between the funnels and the rear superstructure . Close @-@ range defence against torpedo boats was provided by a secondary armament of twelve BL 6 @-@ inch Mk VII guns . Marlborough was also fitted with a pair of QF 3 @-@ inch 20 cwt anti @-@ aircraft guns and four 47 mm ( 1 @.@ 9 in ) 3 @-@ pounder guns . As was typical for capital ships of the period , she was equipped with four 21 in ( 533 mm ) torpedo tubes submerged on the broadside . She was protected by a main armoured belt that was 12 in ( 305 mm ) thick over the ship 's <unk> . Her deck was 2 @.@ 5 in ( 64 mm ) thick . The main battery turret faces were 11 in ( 279 mm ) thick , and the turrets were supported by barbettes 10 in ( 254 mm ) thick . 
