The vessel was a turret ship that was designed by the British Royal Navy Captain Cowper Coles and built by the Samuda Brothers shipyard in Cubitt Town, London as a speculative effort; Prussia purchased the ship during the Second Schleswig War against Denmark, though the vessel was not delivered until after the war.

The Prussians had hoped to secure the vessel by September,[4][5] but delivery was delayed by the British government over the Second Schleswig War between Prussia and Denmark.

[6] At her launching, she was christened Arminius for the victor of the Battle of the Teutoburg Forest against the Romans in 9 CE; the name was chosen to evoke the common feeling of German unity at the time.

This decision was in part made due to heavy ice in the Kieler Förde, which prevented Arminius from entering the port until 4 April 1865.

[10] She was reactivated in May 1866 under the command of Korvettenkapitän (KK—Corvette Captain) Reinhold von Werner, initially to have work done on her gun turrets, but this was delayed as tensions between Austria and Prussia increased.

The Prussians hoped that her presence would intimidate the Austrian commander, Lieutenant Field Marshal Ludwig von Gablenz.

The next day, Arminius was assigned to a squadron commanded by Konteradmiral (Rear Admiral) Eduard von Jachmann, which also included his flagship, the screw frigate Arcona.

[11] The ships arrived in Hamburg, having covered a distance of some 940 nautical miles (1,740 km; 1,080 mi) in 100 hours, an impressive feat for an early ironclad warship.

Unrest broke out in Altona, prompting Werner to send a landing party of one officer and forty men ashore to secure the rail facility in the town.

[13] On 15 June, Arminius, Tiger, and Cyclop, covered the crossing of the Elbe river by General Edwin von Manteuffel and some 13,500 soldiers to attack the city of Hanover.

[9] Arminius, Cyclop, and Tiger sent men ashore at Brunshausen, where they spiked the guns of an abandoned coastal artillery battery.

Arminius entered the Elbe on 17 June, but heavy storms prevented her from intercepting a Norddeutscher Lloyd steamship that was carrying the Hannoverian gold reserves to Britain.

[13] Following the signing of the peace treaty that formally ended the conflict, Werner's flotilla was disbanded on 23 August and Arminius returned to Kiel.

[15] On 3 October, the USS Miantonomoh, a monitor of the US Navy arrived in Kiel while on a promotional tour of European ports; she and Arminius raced the next day, and the latter was two knots faster than the American vessel.

[7][15] Arminius was decommissioned on 20 October, and was only reactivated in 1867 for use as a gunnery training ship to support Thetis, since the latter lacked turret guns.

In June, modernization work on the ship began in Kiel, but in September, she had to be sent to Karlskrona, Sweden, to be dry-docked and have her bottom cleaned.

[15] At the outbreak of the Franco-Prussian War on 19 July 1870, the Prussian Navy concentrated Arminius and the armored frigates Kronprinz, Friedrich Carl, and König Wilhelm in the North Sea naval base at Wilhelmshaven.

She sortied on 27 July under the command of KK Otto Livonius to break through the French blockade by hugging the Swedish coast, which her shallow draft permitted.

[18] Arminius and the three armored frigates, under the command of now Vizeadmiral (Vice Admiral) Jachmann, made an offensive sortie in early August 1870 out to the Dogger Bank, though they encountered no French warships.

[21] In the course of the war, she sortied from the port over forty times; these also failed to result in major combat, though she occasionally traded shots with the blockading French warships.

[15][22] For the majority of the war, Arminius was stationed in the mouth of the Elbe along with the ironclad ram Prinz Adalbert and three small gunboats.

On 23 December, Arminius and the rest of the ships stationed in Wilhelmshaven entered the inner harbor of the port, the dredging of which had recently been completed; the outer Jade Bay had iced over, preventing further operations for the winter.

Beginning on 1 May 1872, the ship was used as a training vessel for naval engineers and boiler room personnel, under the command of KK Philipp von Kall.

The ship was rebuilt again later that year; during the refit the propulsion system was overhauled and replaced with German-built equipment and two searchlights were installed.