German: Oldenburg did not see significant service with the German Navy. She participated in fleet training maneuvers in the late-1880s and early 1890s, but she spent the majority of the 1890s in reserve. Her only major deployment came in 1897–1898 when she joined an international naval demonstration to protest the Greek annexation of Crete. In 1900, she was withdrawn from active duty and used as a harbor defense ship. From 1912 to 1919, she was used by the High Seas Fleet as a target ship; she was sold for scrapping in 1919 and broken up that year.
Following the Franco-Prussian War of 1870–1871, General Albrecht von Stosch became the Chief of the Imperial Admiralty; he immediately set about drafting a new fleet plan that was based on the previous program that had been approved in 1867. Stosch saw the role of the navy as primarily defensive; a fleet of ironclad warships would be kept in German waters to defend the coast against the type of blockade the Danish Navy had imposed during the Second Schleswig War and the French Navy had put into place during the Franco-Prussian conflict. Stosch's fleet plan, finalized in 1873, called for a total of eight ocean-going ironclads and six smaller, armored corvettes suited for operations in coastal waters. The ocean-going component had been completed with the, and of the six corvettes, five had been built: and the four s. The last corvette was originally intended to be a fifth German: Sachsen-type vessel, but dissatisfaction with the design led many senior officers to push for a revised version.
Work on the new design began in 1879, but parliamentary objections to naval expenditures, particularly after the accidental sinking of the ironclad in 1878, delayed construction of the vessel. Stosch initially sought to secure funding for two ships of the design, with the intention to retain one as a material reserve to be mobilized in the event of war, but the German: [[Reichstag (German Empire)|Reichstag]] refused. Stosch proposed the new vessel for the 1879–1880 fiscal year, which was refused, leading him to drop the request for the next year's budget. Finally on 7 December 1881, the parliament voted to approve funds for German: Oldenburg, albeit an amount significantly less than the navy desired. The budgetary constraints severely limited the ability of the design staff to produce an effective improvement on the German: Sachsens. On the available budget, the new ship's displacement would have to be reduced by some compared to the German: Sachsens. The limited displacement forced a reversion to the casemate ship arrangement, as well as a reduction in the caliber of guns from to . To somewhat offset the reduction in offensive power, these guns were of a new, longer 30-caliber type that had a higher muzzle velocity than the shorter 22-caliber guns carried by the German: Sachsen class.
Assessment of the design is mixed; the ship was an anachronism, being the last casemate ship to be laid down by any navy (though the Ottoman ironclad was completed later). The naval historian Erich Gröner states that German: Oldenburg was an "experimental design, of no real value in combat." Conway's All the World's Fighting Ships concurs, stating that German: Oldenburg was "considered to be of little fighting value by the time she was completed." The historian Aidan Dodson criticized the ship as being "a poor investment [that] failed to make her designed speed by and had a form that lead to a rapid drop-off of speed in head seas." The 1889 edition of the Brassey's Naval Annual reported a contradictory opinion, however, stating that "The majority of German naval critics are dissatisfied to a greater or less extent with all of these vessels, the,,, and German: Oldenburg excepted."
German: Oldenburg was long at the waterline and long overall. She had a beam of and a draft of forward and aft. As designed, the vessel displaced 5249MT, and when fully loaded, her displacement increased to 5743MT. Her hull was constructed with transverse and longitudinal steel frames; iron was used for the stem and stern. The hull was divided into twelve watertight compartments and incorporated a double bottom that ran for 60 percent of the length of its length. As was common for capital ships of the era, German: Oldenburgs hull was fitted with a pronounced ram bow. The ship had a conning tower forward with a short hurricane deck directly astern; a smaller, secondary conning position was placed further aft. The ship was fitted with a single heavy military mast with a fighting top, which was located amidships. A smaller pole mast was placed near the stern. German: Oldenburg was the first German capital ship built entirely from German-made steel, apart from her stern.
The German navy regarded German: Oldenburg as an adequate sea boat, though she suffered from significant pitching. As a result of her tendency to pitch severely, a 60MT ballast was permanently installed in the bow. She also lost a great deal of speed in heavy seas; at conditions above Beaufort sea state 6, this could be up to a 25 percent loss of speed. The ship could not operate under severe weather conditions. Her transverse metacentric height was 0.63m (02.07feet). Her standard complement consisted of 34 officers and 355 enlisted men, though her crew was later reorganized to 32 officers and 401 enlisted sailors. She carried a number of smaller boats, including one picket boat, one launch, two pinnaces, two cutters, two yawls, and one dinghy.
German: Oldenburg was powered by two horizontal 4-cylinder double-expansion steam engines in separate engine rooms; the two engines each drove a three-bladed screw propeller that was 4.5m (14.8feet) in diameter. Steam was provided to the engines by eight transverse, cylindrical fire-tube boilers, divided into two boiler rooms. Each boiler was equipped with three fireboxes, for a total of 24, which operated at up to 5atm using forced draft. The boiler rooms were vented through a pair of funnels, which were placed fore and aft of the main mast. The engines were designed to operate at 3900PS for a top speed of 14kn. On speed trials, her engines slightly exceeded the designed horsepower, at 3942PS, though German: Oldenburg made only .
The ship's coal storage was severely limited due to the size constraints imposed by the authorized budget. She was designed to store 348MT of coal normally, though she could accommodate up to 450MT under wartime conditions. An additional 120MT of coal could be stored on her deck for longer voyages. At a cruising speed of, German: Oldenburg could steam for 1770nmi. Increasing her speed by one knot reduced her range to 1370nmi, and at, she could cruise for only 980nmi. In comparison, the German: Sachsen-class ships could steam for at 10 knots. Steering was controlled by a single rudder. She was equipped with three electric generators with a total output of 29 kilowatts at 65 volts.
German: Oldenburg carried eight 24cm (09inches) L/30 hooped guns in an unusual configuration: six guns on the main deck, one on each broadside, four in embrasures at each corner of the central battery, which was sponsoned over the hull to give a measure of end-on fire, and two on the upper deck firing broadside. These guns were supplied with 494 rounds of ammunition, and could depress to −5° and elevate to 8°. This enabled a maximum range of 5700to. Her secondary battery consisted of four 15cm (06inches) L/22 guns in single mounts. For close-range defense against torpedo boats, she carried a pair of 8.7cm (03.4inches) L/24 guns in single mounts. Later in her career, she received another six of these guns to strengthen her defensive capabilities. Four torpedo tubes rounded out her armament. One was mounted in the bow, submerged, two were placed on the broadside above water, and the fourth was located in the stern, also above water. She carried ten torpedoes.
German: Oldenburgs armor consisted of compound steel backed with teak; the steel was fabricated by the Dillinger Works. The main armored belt was composed of two strakes; the steel upper strake was thick in the central citadel, where it protected the ship's vitals. The belt was reduced on either end of the central portion to 200mm. The lower strake was 250mm thick in the central section and 180mm on either end. The entire belt was backed with 250 mm of teak amidships and 300 mm of teak on either end. The sides of the armored casemates for the main battery were 150mm thick. The ship's deck was 30mm thick. Her forward conning tower had thick sides and a 25mm thick roof. The rear conning tower was given only splinter protection, with 15mm thick sides and a 12mm thick roof.
German: Oldenburg was laid down in the spring of 1883 at the AG Vulcan shipyard in Stettin, under yard number 132. She was launched on 20 December 1884, where the ship was christened by Friedrich August, who would go on to be the grand duke of Oldenburg, the ship's namesake. Fitting-out work thereafter commenced. She was completed by April 1886 and commissioned into the German Navy on 8 April, thereafter beginning sea trials under the command of German: [[Kapitän zur See]] (KzS—Captain at Sea) Heusner. Following their conclusion on 30 July, German: Oldenburg joined I Division of the fleet, alongside,, and, for the annual fleet maneuvers held in August and September. German: Bayern and German: Württemberg suffered from engine troubles throughout the exercises, but German: Oldenburg performed satisfactorily. After the end of the exercises in September, German: Oldenburg was assigned as the guard ship for Kiel, where she also conducted further sea trials under the command of German: [[Korvettenkapitän]] (KK——Corvette Captain) Max Plüddemann. On 23 December, she was decommissioned for the winter.
On 3 March 1887, German: Oldenburg was recommissioned to serve with the active squadron that year. In June, Germany began work on the Kaiser Wilhelm Canal; German: Oldenburg was among the ships present during the celebration marking the event. German: Oldenburg was assigned to the training squadron for the maneuvers in August–September 1887, along with German: König Wilhelm and German: Kaiser. The majority of the exercises were focused in the Baltic, but the fleet did conduct maneuvers in the North Sea for eight days in September. German: Oldenburg was decommissioned again for the winter on 21 October in Kiel. She remained out of service through 1888, and was recommissioned on 1 May 1889, under the command of KzS Ernst Aschmann. German: Oldenburg participated in the visit to Great Britain in August, where Wilhelm II took part in the Cowes Regatta. The ship was assigned to I Division with German: Sachsen,, and the new cruiser . German: Oldenburg and the rest of the fleet joined the Royal Navy in a fleet review for Queen Victoria. After returning to Germany, the ships took part in the fleet maneuvers. German: Oldenburg was assigned as a guard ship on 14 September; she was also used as a training ship for engine room crews.
German: Oldenburg returned to active service with I Division in 1890. In June and July, she took part in Wilhelm II's state visit to Copenhagen, Denmark, and Christiana, Norway. After returning from the cruise in Scandinavian waters, German: Oldenburg and the rest of the division participated in the ceremonial transfer of the island of Helgoland from British to German control. She was present during the fleet maneuvers in September, where the entire eight-ship armored squadron simulated a Russian fleet blockading Kiel. German: Oldenburg thereafter went to Wilhelmshaven on the North Sea, where she resumed defense and training duties on 30 September.
She remained with I Division in 1891. In late February, she embarked German: [[Vizeadmiral]] (Vice Admiral) Max von der Goltz to Britain to witness the launchings of the new pre-dreadnought battleship and the armored cruiser at the invitation of the British Admiralty. The visit lasted into early March, and while the ship was in Britain, a detachment of her crew was sent to participate in a military parade for Queen Victoria. German: Oldenburg rejoined I Division on 1 May, and the year's maneuvers simulated a two-front war against Russia and either France or Denmark. German: Oldenburgs deficiencies as a warship, particularly her insufficient radius of action, were highlighted during these exercises. Especially revealing was the fact that she had to be towed back to port after she ran out of coal. That year, the German fleet was reorganized and a training squadron of ironclads was kept in commission through the winter, though German: Oldenburg was assigned to the Reserve Division of the North Sea, at that time coming under the command of KzS Alfred Herz. On 31 December, riots broke out among the ship's crew, which was quickly suppressed; the participants were subsequently tried in courts martial.
The ship was reactivated in early 1892 and reassigned to I Division to participate in the normal routine of training exercises and voyages abroad. These were interrupted on 14 July when the ship's engines broke down while she was cruising off Helgoland. After determining the extent of the damage, she was decommissioned on 6 August. As a result, German: Württemberg replaced German: Oldenburg in I Division, and the latter went into reserve for repairs. She remained out of service for the next five years, before being reactivated on 1 October 1897 to replace the old ironclad German: König Wilhelm in II Division of I Battle Squadron. On 1 December, she departed for the Mediterranean to join an international naval demonstration off the island of Crete, which Greece had sought to annex. On the way there, German: Oldenburg was forced to stop in El Ferrol, Spain, to take on more coal, and she arrived Suda Bay, Crete, on 6 January 1898. There, she relieved the protected cruiser, which was in turn sent to join the East Asia Squadron. German: Oldenburg had been sent because there were no other warships available, despite her shortcomings. Her inadequacy was clear to the men of the other navies present, who nicknamed the ship "baby of war". She nevertheless contributed a landing party to an international force ashore. The ship remained in the demonstration until 16 March, when Germany and Austria-Hungary withdrew their naval contingents in a show of dissatisfaction over the compromise solution, which left Crete under Ottoman control, but with a Greek prince.
German: Oldenburg stopped in Messina, Italy, from 19 to 27 March before resuming the voyage home. The ship was interrupted again while in Málaga, Spain, by the outbreak of the Spanish–American War; she was ordered to remain in the area in the event that Germany's ambassador had need of the vessel. During this period, she carried envoys around Morocco, from Tangier to Mazagan and then to Marrakesh, where the envoy presented his credentials to the Moroccan government. German: Oldenburg remained in Cadiz, Spain, from mid-April to mid-May; during this period, the ship's executive officer, German: [[Kapitänleutnant]] (Captain Lieutenant) Günther von Krosigk, was sent as a liaison with the Spanish naval command. The ship later went to Lisbon, Portugal, for the celebration commemorating the 400th anniversary of the return of Vasco da Gama after his first voyage to India. She once again was a poor representation of Germany amongst the foreign vessels assembled for the event. German: Oldenburg then returned to Tanger, where she lay from late May to early July. She then received orders to return home, passing through El Ferrol on 12 July, and arriving off Helgoland eight days later. The ship rejoined II Division of I Squadron and took part in the annual training cycle for the rest of the year.
On 22 March 1899, while steaming off Bülk in a heavy snow storm, German: Oldenburg ran aground and could not free herself, particularly after sand got into her condensers. The crew had to remove the ship's guns and ammunition before she could be pulled free. She was present for a celebration of the 50th anniversary of a battle during the First Schleswig War between German artillery batteries and Danish warships. German: Oldenburg was detached from I Squadron shortly thereafter, and on 23 April, she was decommissioned in Wilhelmshaven. From 1900, she was used as a guard ship and later as a depot ship, and she was towed to Kiel in early January 1904. She was stricken from the naval register on 13 January 1912. The vessel was used as a target ship by the High Seas Fleet and was accidentally grounded at Stollergrund in a storm in May 1913, where she continued to be used as a target until after the German defeat in World War I. German: Oldenburg was sold to Hattinger Company, a ship-breaking firm, on 5 May 1919. The ship was dismantled for scrap in Wilhelmshaven that year.