Coastal defense breastwork monitor of the French Navy
Tonnerre was the lead ship of a class of two coastal defense breastwork monitors built for the French Navy () in the 1870s. Armed with a main armament of two Modèle 1875 guns mounted in a single turret that had armor thick, the ship was Launched in 1875, the vessel was originally commissioned into reserve at Brest. As French naval doctrine moved from a fleet of smaller coastal defense ships to larger ocean-going battleships, the ship "Tonnerre" had an uneventful career. Between 1884 and 1885, the ship served in the Evolution Squadron () but joined the Northern Squadron () in 1891. As part of a naval exercise in 1893, the vessel participated in the successful defence of Cherbourg against a superior force. The ship was struck in 1905 and, after serving as a target, was sold after 1920. 
Design and description.
On 10 November 1871, the Minister of the Navy () Louis Pierre Alexis Pothuau issued a specification for a new coastal defense ship. Of the three alternatives submitted on 9 August 1872, the French Navy accepted that developed by Louis de Bussy, which was signed on 29 July. The design was based on his existing second-class coastal defense ships, as epitomised by the , but with an armored deck raised by , sitting above the waterline and all vertical dimensions increased by 25 percent. With similarity to the Royal Navy monitor but with a shorter breastwork, the design was agreed and built as class of two vessels, the first named "Tonnerre".
A breastwork monitor that had hull of steel, "Tonnerre" had a single turret forward and a narrow superstructure wide aft. The vessel displaced , had an overall length of , at the waterline and between perpendiculars. The ship's beam was at the waterline and draught was mean and aft. The ship's complement numbered 190 sailors of all ranks.
"Tonnerre" was powered by a reconditioned engine that had previously powered the ironclad . It was a single horizontal simple expansion steam engine that drove one propeller shaft. Steam was provided by eight reinforced high rectangular tubular boilers that were designed to run at a pressure of . The engine had two cylinders, each of bore and stroke. The engine was rated at at 60rpm. While undertaking sea trials, "Tonnerre" reached a speed of from . The ship carried of coal, which gave a range of at a cruising speed of . In service, the ship was rated at .
"Tonnerre" carried a main battery of two 19.75-caliber Modèle 1875 guns in a single enclosed turret. The guns were capable of firing every seven or eight minutes. The guns were hydraulically loaded, as were the turrets. The guns were designed to fire astern, but doing so damaged the superstructure. Defence from torpedo boats was provided by four 17-caliber 12-pounder bronze guns mounted at the corners of the flying deck, raised above the hull. The ship was equipped with a ram. Six Hotchkiss revolving cannons were added, which were replaced, in 1900, by six Canon de Modèle 1885 Hotchkiss guns and two Hotchkiss revolving cannons. Four Mangin searchlights were also added during the ship's time in service.
The ship was fitted with wrought iron armor with a full-length waterline armor belt that tapered from the maximum thickness of amidships to forward and aft. The deck armor was thick amidships with ends had of wood mounted on plating. The belt stretched from below the waterline to above. The breastwork had armor that was amidships and 300 mm at the ends. The turret was also protected by armor that is 300 mm thick, although the gun ports themselves were thick. The turret was in diameter. A cylindrical conning tower was mounted on the turret, supported by a fixed shaft that ran through the turret.
Construction and career.
Laid down in January 1873 by the naval shipyard at Lorient, "Tonnerre" was launched on 16 September 1875. Initially commissioned for trials on 15 September 1877, the ship was fully commissioned on 1 April the following year. The vessel was transferred to Brest, arriving on 22 June, and placed in reserve. Between 1884 and 1885 the ship served with the Evolution Squadron (), before being returned to reserve at Cherbourg. In 1891, "Tonnerre" was commissioned into the Armored Division () of the Northern Squadron () On 26 July, "Tonnerre" joined fellow ironclads and on a naval exercise. The flotilla was instructed to defend Cherbourg from a more powerful force of ironclads, cruisers and torpedo boats. They were successful in deterring the attacking force and, on 3 August, the ship participated in an attack against the enemy using dummy torpedoes.
On 7 September 1894, it was announced that the vessel was to be retired from active service and replaced by the newer ironclad . French naval doctrine was changing and the focus on coastal defense was being replaced by one of larger sea-going warships. The size of ships was also increasing, and newer, more capable battleships entered service. After being reboilered and rearmed in 1900, the ship served for five years before being struck on 12 December 1905. After serving as a target at Brest for one year and at Lorient for another twelve, "Tonnerre" was retired. The ship was put up for sale at Lorient between 1920 and 1922.
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