 The ship was armed with a main battery of two 340 @-@ millimeter ( 13 @.@ 4 in ) <unk> 28 @-@ caliber guns and two slightly newer M1884 guns of the same caliber . These weapons were mounted in individual barbettes in a " lozenge " arrangement , with one gun forward , one aft , and two amidships . The secondary battery consisted of sixteen 138 @.@ 6 mm ( 5 @.@ 46 in ) M1884 quick @-@ firing ( QF ) guns , all firing through unarmored embrasures in the hull . Marceau 's light armament varies widely between sources : Chesneau & Kolesnik give a range of three to six 65 mm ( 2 @.@ 6 in ) 9 @-@ pounder guns , nine to eighteen 47 mm ( 1 @.@ 9 in ) 3 @-@ pounder guns , eight to twelve 37 mm ( 1 @.@ 5 in ) 1 @-@ pounder five @-@ barrel Hotchkiss revolving cannon , and three to five 450 mm ( 18 in ) torpedo tubes in deck @-@ mounted launchers ; naval historian Eric Gille gives four to seven 65 mm guns , nine to twelve 47 mm guns , eight 37 mm guns and five to six torpedo tubes , all above water ; naval historian Paul Silverstone says six 65 mm guns , twelve 47 mm guns and five torpedo tubes . The ship 's compound armor belt was 450 mm ( 17 @.@ 7 in ) thick amidships and reduced to 300 mm ( 11 @.@ 8 in ) at the stern and 230 mm ( 9 @.@ 1 in ) . The barbettes were also 450 mm thick . The conning tower was protected by 120 mm ( 4 @.@ 7 in ) of armor plating and the deck was 80 mm ( 3 @.@ 1 in ) thick . 
