French ironclad Marengo

Marengo was a wooden-hulled, Océan-class ironclad, armored frigate, 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 ironclads were designed by Henri Dupuy de Lôme as an improved version of the Provence-class ironclads. 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 87.73 m overall, with a beam of 17.52 m. Marengo had a maximum draft of 9.09 m and displaced 7749 t. Her crew numbered between 750 and 778 officers and men. The metacentric height of the ship was very low, between 1.7 - 2.2 ft.

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 3600 ihp and Marego reached 13.5 kn. She carried 650 MT of coal which allowed her to steam for approximately 3000 nmi at a speed of 10 kn. The Océan-class ships were barque or barquentine-rigged with three masts and had a sail area around 2000 sqm.

Armament
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 mm guns in the barbettes, and on the battery deck, four 240 mm and seven 138 mm guns. By 1885 two more 274-millimeter guns had been added and all of the 138-millimeter guns were replaced by four 120 mm guns.

The 18-caliber 274-millimeter Modéle 1870 gun fired an armor-piercing, 476.2 lb shell while the gun itself weighed 22.84 LT. The gun fired its shell at a muzzle velocity of 1424 ft/s and was credited with the ability to penetrate a nominal 14.3 in of wrought iron armour at the muzzle. The armor-piercing shell of the 19-caliber 240-millmeter Modele 1870 gun weighed 317.5 lb while the gun itself weighed 15.41 LT. It had a muzzle velocity of 1624 ft/s and was credited with the ability to penetrate a nominal 14.4 in of wrought iron armour at the muzzle. The 138-millimeter gun was 21 calibers long and weighed 2.63 LT. It fired a 61.7 lb explosive shell that had a muzzle velocity of 1529 ft/s. The guns could fire both solid shot and explosive shells.

At some point the ship received a dozen 37 mm Hotchkiss 5-barrel revolving guns. They fired a shell weighing about 500 g at a muzzle velocity of about 610 m/s to a range of about 3200 m. 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 356 mm torpedo tubes were added.

Armor
The Ocean-class ships had a complete 178 - 203 mm wrought iron waterline belt. The sides of the battery itself were armored with 160 mm of wrought iron. The barbette armor was 150 mm thick. The unarmored portions of their sides were protected by 15 mm 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 Toulon 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 (Division Navale du Levant) 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.