Alma-class ironclad

The Alma-class ironclads were a group of seven wooden-hulled, armored corvettes built for the French Navy in the mid to late 1860s. Three of the ships attempted to blockade Prussian ports in the Baltic Sea in 1870 during the Franco-Prussian War. Three others patrolled the North Sea and the Atlantic, while the last ship was en route to Japan when the war began and blockaded two small Prussian ships in a Japanese harbor. Afterwards they alternated periods of reserve and active commissions, many of them abroad. Three of the ships participated in the French occupation of Tunisia in 1881 while another helped to intimidate the Vietnamese Government into accepting status as a French protectorate and played a small role in the Sino-French War of 1884–85.

Design and description
The Alma-class ironclads were designed by Henri Dupuy de Lôme as improved versions of the armored corvette FRENCH IRONCLAD Belliqueuse suitable for foreign deployments. Unlike their predecessor the ships were true central battery ironclads as they were fitted with armored transverse bulkheads. The original plan for these ships was to have a two-deck battery with four 194 mm guns on the battery deck and four 164 mm guns mounted above them on the upper deck, one gun at each corner of the battery. This design was changed to substitute four barbettes for the upper battery, but the addition of armored bulkheads proved to be very heavy and the rear pair of barbettes had to be deleted to save weight. In partial compensation the 164-millimeter guns in the barbettes were replaced by an additional pair of 194-millimeter guns. Like most ironclads of their era they were equipped with a metal-reinforced ram.

The ships were built from the same general plan, but differed amongst themselves. They measured 68.75 - 69.03 m between perpendiculars, with a beam of 13.94 - 14.13 m. The ships had a mean draft of 6.26 - 6.66 m and displaced 3569 - 3889 t. Their crew numbered 316 officers and men.

Propulsion
The Alma-class ships had a single horizontal return connecting-rod steam engine driving a single propeller. Their engine was powered by four oval boilers. On sea trials the engine produced between 1585 - 1896 ihp and the ships reached 10.48 - 11.99 kn. Unlike the single funnels of the others, FRENCH IRONCLAD Jeanne d'Arc and FRENCH IRONCLAD Thétis had two funnels, mounted side-by-side. The ships carried 250 MT of coal which allowed the ship to steam for 1310 - 1620 nmi at a speed of 10 kn. They were barque-rigged with three masts and had a sail area between 1338 - 1454 sqm.

Armament
The ships mounted four of their 194-millimeter Modèle 1864 breech-loading guns in the central battery on the battery deck. The other two 194-millimeter guns were mounted in barbettes on the upper deck, sponsoned out over the sides of the ship. The four 120 mm guns were also mounted on the upper deck. FRENCH IRONCLAD Alma is the only ship positively known to have exchanged her 194 mm guns for newer Modèle 1870 guns. The armor-piercing shell of the 20-caliber Mle 1870 gun weighed 165.3 lb while the gun itself weighed 7.83 LT. The gun fired its shell at a muzzle velocity of 1739 ft/s and was credited with the ability to penetrate a nominal 12.5 in of wrought iron armour at the muzzle. The guns could fire both solid shot and explosive shells.

Armor
The Alma-class ships had a complete 150 mm wrought iron waterline belt, approximately 2.4 m high. The sides of the battery itself were armored with 120 mm of wrought iron and the ends of the battery were closed by bulkheads of the same thickness. The barbette armor was 100 mm thick, backed by 240 mm of wood. The unarmored portions of their sides were protected by 15 mm iron plates.

Service
During the Franco-Prussian War of 1870–71 Thétis, Jeanne d'Arc and Armide were assigned to the Northern Squadron that attempted to blockade Prussian ports on the Baltic until ordered to return to Cherbourg on 16 September 1870. Montcalm, Atalante, and Reine Blanche cruised the North Sea and Montcalm later watched a Prussian corvette in Portuguese waters. Alma was en route to the Far East when the war began and she blockaded a pair of Prussian corvettes in Yokohama harbor once she arrived at Japan.

After the end of the war many of the ships were placed in reserve or sent to foreign stations, often as the flagship. During the Third Carlist War of 1872–76 Thétis, Reine Blanche and Jeanne d'Arc spent time in Spanish waters where they could protect French citizens and interests. In 1875 the latter ship rammed and sank the dispatch vessel Forfait. On 3 July 1877 Thétis rammed Reine Blanche who had to be run ashore to prevent her from sinking.

Further abroad Reine Blanche and Alma bombarded the Tunisian port of Sfax in July 1881 as part of the French occupation of Tunisia. Atalante participated in the Battle of Thuan An in August 1883. This was an attack by the French on the forts defending the mouth of the Perfume River, leading to the Vietnamese capital of Huế in an attempt to intimidate the Vietnamese government. During the Sino-French War of 1884–85 the ship was in Huế in early September 1884, but she carried Admiral Amédée Courbet to Keelung, Taiwan on 23 September.