Muin-i Zafer, meaning "Aid to Triumph" in Ottoman Turkish, was the second of two Avnillah-class casemate ironclads built for the Ottoman Navy. She was ordered in 1867 from the Samuda Brothers shipyard at Cubitt Town in London, laid down in 1868, launched in June 1869, and commissioned into the fleet in 1870.
The ship was 68.9 metres long, with a beam of 10.9 metres and a draft of 5 metres. Her iron hull incorporated a partial double bottom and displaced 2,362 metric tons. She carried a complement of 15 officers and 130 enlisted men. She was powered by a single horizontal compound steam engine driven by four coal-fired box boilers, all trunked into a single funnel amidships, rated at 2,200 indicated horsepower and producing a top speed of 12 knots. A supplementary brigantine sail rig was also fitted for use when economising on coal. Her main armament consisted of four 228 mm muzzle-loading guns mounted in a central armoured casemate, two guns per side, positioned so that any two could fire directly ahead, astern, or to either broadside. The armoured belt ranged from 127 to 152 mm in thickness, and the casemate itself was protected by 152 mm of iron plating.
Upon commissioning, Muin-i Zafer was assigned to the II Squadron of the Asiatic Fleet, alongside her sister ship Avnillah and the ironclads Hifz-ur Rahman and Lütf-ü Celil. The Ottoman fleet, under Hobart Pasha, was deployed to Crete to help stabilise the island following the Cretan Revolt of 1866–1869, though it remained largely inactive during this period, with training confined to reading translated British instruction manuals. In these early years, the fleet's ironclads would make short summer cruises to keep their engines in working order.
It was during the Russo-Turkish War of 1877–1878 that Muin-i Zafer saw real action. The Ottoman fleet began mobilising in September 1876 as tensions with Russia mounted, and in December 1876, Muin-i Zafer and her sister Avnillah were transferred to Batumi owing to increasingly active Russian naval forces in the area. The war began on 24 April 1877 with a Russian declaration of war. The eight Ottoman ironclads in the Black Sea, commanded by Hobart Pasha, were vastly superior to the Russian Black Sea Fleet; the only ironclads the Russians possessed there were the Vitse-admiral Popov and Novgorod, circular vessels that had proved largely useless in service. The presence of the Ottoman fleet did force the Russians to keep two corps in reserve for coastal defence, but the Ottoman high command failed to make more meaningful use of its naval superiority, particularly to hinder the Russian advance into the Balkans.
The fleet attacked the city of Poti and helped defend Batumi. On 14 May 1877, Muin-i Zafer was part of an Ottoman squadron that bombarded Russian positions near Sokhumi, landed soldiers, and armed the local population to foment a rebellion against the Russians. The Ottomans captured Sokhumi two days later. Later in the campaign, Muin-i Zafer also helped defend the port of Sulina at the mouth of the Danube, where her role was to protect the port from seaward attack and support the shore fortifications.
Following the war, Muin-i Zafer was placed in reserve at Istanbul. By 1892, decades of poor maintenance had reduced her speed to just 8 knots. In 1882, a pair of 87 mm breech-loading Krupp guns were added to her armament. The Ottomans also planned to further strengthen the ship with additional smaller-calibre Krupp and Hotchkiss guns and a torpedo tube, but these plans came to nothing. At some point the brigantine rig was removed and replaced with military masts.
When the Turco-Greek War began in 1897, an Ottoman inspection found almost all the ironclads, including Muin-i Zafer, to be completely unfit for combat, their hulls rotting and their crews poorly trained. This proved an embarrassment that finally forced Sultan Abdülhamit II to authorise a modernisation programme. Krupp was initially awarded the reconstruction contract in August 1900, but withdrew in December 1902, and the Italian firm Gio. Ansaldo & C. took over the project. The reconstruction was carried out between 1903 and 1906 at the Ottoman Imperial Arsenal, which was in part leased to Ansaldo to cover the cost. The ship emerged with her old muzzle-loaders replaced by four quick-firing 150 mm Krupp 40-caliber guns and a new light battery of six 75 mm quick-firing Krupp guns.
By 1910, Muin-i Zafer had become a stationary guard ship at İzmir, with most of her weapons removed. When the Italo-Turkish War broke out in September 1911, she was serving as a guard ship at Beirut but soon withdrew to Port Said at the entrance to the Suez Canal, where her remaining guns were landed to reinforce the shore defences. Her sister ship Avnillah was less fortunate as she was attacked and sunk at the Battle of Beirut in early 1912 by Italian armoured cruisers.
As Muin-i Zafer's fighting days drew to a close, she transitioned through a succession of support roles that reflected the changing needs of the Ottoman and later Turkish Navy. She served as a torpedo training ship from 1913, a floating barracks from 1920, and a submarine depot ship from 1928. She was finally decommissioned in 1932 and broken up for scrap in 1934, ending a career that had spanned more than six decades, from the age of ironclad broadside warships to the era of submarines.
