 These ships had their main armament mounted in four barbettes on the upper deck, one gun at each corner of the battery, with the remaining guns on the battery deck below the barbettes. Marengo's armament was upgraded, before she commissioned, to four 274-millimeter (10.8 in) guns in the barbettes, and on the battery deck, four 240-millimeter (9.4 in) and seven 138-millimeter (5.4 in) guns. By 1885 two more 274-millimeter guns had been added and all of the 138-millimeter guns were replaced by four 120-millimeter (4.7 in) guns.
