French ironclad Marengo Marengo was a wooden - hulled , armored frigate of the , built for the French Navy in the mid to late 1860s . The ship was running her sea trials in July 1870 when the Franco - Prussian War began and was immediately placed in reserve until after the war was over . " Marengo " participated in the French occupation of Tunisia in 1881 and was flagship of the Northern Squadron in 1891 when it made port visits in Britain and Russia . She was sold for scrap in 1896 . Design and description . The " Océan " - class ironclad s were designed by Henri Dupuy de Lôme as an improved version of the s . The ships were central battery ironclads with the armament concentrated amidships . For the first time in a French ironclad three watertight iron bulkheads were fitted in the hull . Like most ironclads of their era they were equipped with a metal - reinforced ram . The ship measured overall , with a beam of . " Marengo " had a maximum draft of and displaced . Her crew numbered between 750 and 778 officers and men . The metacentric height of the ship was very low , between . Propulsion . The " Océan " - class ships had one horizontal return connecting rod compound steam engine driving a single propeller . Their engines were powered by eight oval boilers . On sea trials the engine produced and " Marego " reached . She carried of coal which allowed her to steam for approximately at a speed of . The " Océan " - class ships were barque or barquentine - rigged with three masts and had a sail area around . Armament . These ships had their main armament mounted in four barbette s 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 guns in the barbettes , and on the battery deck , four and seven guns . By 1885 two more 274 - millimeter guns had been added and all of the 138 - millimeter guns were replaced by four guns . The 18 - caliber 274 - millimeter Modéle 1870 gun fired an armor - piercing , shell while the gun itself weighed . The gun fired its shell at a muzzle velocity of and was credited with the ability to penetrate a nominal of wrought iron armour at the muzzle . The armor - piercing shell of the 19 - caliber 240 - millmeter Modele 1870 gun weighed while the gun itself weighed . It had a muzzle velocity of and was credited with the ability to penetrate a nominal of wrought iron armour at the muzzle . The 138 - millimeter gun was 21 calibers long and weighed . It fired a explosive shell that had a muzzle velocity of . The guns could fire both solid shot and explosive shells . At some point the ship received a dozen Hotchkiss 5 - barrel revolving guns . They fired a shell weighing about at a muzzle velocity of about to a range of about . They had a rate of fire of about 30 rounds per minute . The hull was not recessed to enable any of the guns on the battery deck to fire forward or aft . However , the guns mounted in the barbettes sponsoned out over the sides of the hull did have some ability to fire fore and aft . Late in the ship ' s career four above - water torpedo tube s were added . Armor . The " Ocean " - class ships had a complete wrought iron waterline belt . The sides of the battery itself were armored with of wrought iron . The barbette armor was thick . The unarmored portions of their sides were protected by iron plates . Gardiner says that the barbette armor was later removed to improve their stability , but this is not confirmed by any other source . Service . " Marengo " was laid down at Brest in July 1865 and launched on 15 October 1868 . The ship began her sea trials on 1 July 1870 and was running them when the Franco - Prussian War of 1870 – 71 began . She was immediately put in reserve and not commissioned until 1872 for service with the Mediterranean Squadron . Marengo remained with the squadron until 1876 when she was again placed in reserve . On 2 October 1880 the ship was recommissioned and assigned to the Mediterranean Squadron . " Marengo " was transferred to the Levant Squadron ( ) on 13 February 1881 and bombarded the Tunisian port of Sfax in July as part of the French occupation of Tunisia . She remained in the Mediterranean until 1886 when she was assigned to the Reserve Squadron . In 1888 " Marengo " became the flagship of the Northern Squadron and led the squadron during its port visits to Osborne Bay and Spithead in August 1891 and to Kronstadt in September 1891 . She was reduced to reserve the following year and sold on 7 March 1896 .