SMS Posen[b] was one of four battleships in the Nassau class, the first dreadnoughts built for the German Imperial Navy (Kaiserliche Marine).

The ship was laid down at the Germaniawerft shipyard in Kiel on 11 June 1907, launched on 12 December 1908, and commissioned into the High Seas Fleet on 31 May 1910.

In the confusion, the ship accidentally rammed the light cruiser SMS Elbing, which suffered serious damage and was scuttled later in the night.

Over the next two years, the design was refined into a larger vessel with twelve of the guns, by which time Britain had launched the all-big-gun battleship HMS Dreadnought.

[5] This type of machinery was chosen at the request of both Admiral Alfred von Tirpitz and the Navy's construction department; the latter stated in 1905 that the "use of turbines in heavy warships does not recommend itself.

For the 1914 cruise, the fleet departed for Norwegian waters on 14 July, some two weeks after the assassination of Archduke Franz Ferdinand in Sarajevo.

[16] Posen and the rest of the fleet conducted several advances into the North Sea to support Rear Admiral Franz von Hipper's I Scouting Group battlecruisers.

[18] On the evening of 15 December, the German battle fleet of 12 dreadnoughts—including Posen and her three sisters—and eight pre-dreadnoughts came to within 10 nmi (19 km; 12 mi) of an isolated squadron of six British battleships.

Under orders from Kaiser Wilhelm II to avoid risking the fleet unnecessarily, Ingenohl broke off the engagement and turned the battlefleet back toward Germany.

The assembled German flotilla included Posen and her three sister ships, the four Helgoland-class battleships, the battlecruisers Von der Tann, Moltke, and Seydlitz, and several pre-dreadnoughts, operating under the command of Hipper, now a vice admiral.

[1] On the 17th, Posen and Nassau engaged Slava at long range; they scored three hits on the Russian ship and forced her to return to port.

[22] Admiral Hipper later remarked, "To keep valuable ships for a considerable time in a limited area in which enemy submarines were increasingly active, with the corresponding risk of damage and loss, was to indulge in a gamble out of all proportion to the advantage to be derived from the occupation of the Gulf before the capture of Riga from the land side."

On 4 March 1916, Posen, Nassau, Westfalen, and Von der Tann steamed out to the Amrumbank to receive the auxiliary cruiser Möwe, which was returning from a raiding mission.

A bombardment mission followed two days later; Posen joined the battleship support for Hipper's battlecruisers while they attacked Yarmouth and Lowestoft on 24–25 April.

The damage to Seydlitz and condenser trouble on several of the III Battle Squadron dreadnoughts delayed the plan until the end of May.

[2] Between 17:48 and 17:52, Posen and ten other German battleships engaged the British 2nd Light Cruiser Squadron, though the range and poor visibility prevented effective fire.

Posen was the only ship of I Battle Squadron to be able to make out a target, which turned out to be the battlecruisers HMS Princess Royal and Indomitable.

A violent firefight at close range ensued; the leading German battleships, including Posen, opened fire on several British warships.

[32] Two and a half hours later, Elbing spotted several approaching British destroyers, and her captain gave the order to scuttle the ship.

[34] At 01:25, Westfalen illuminated the destroyer Ardent and opened fire; Posen joined her shortly thereafter and reported several hits at ranges of 1,000 to 1,200 m (1,100 to 1,300 yd).

[35] Despite the ferocity of the night fighting, the High Seas Fleet punched through the British destroyer forces and reached Horns Reef by 04:00 on 1 June.

[36] The German fleet reached Wilhelmshaven a few hours later, where Posen and several other battleships from I Battle Squadron took up defensive positions in the outer roadstead.

[24] Beginning in June 1917, Wilhelm von Krosigk served as the ship's commanding officer; he held this position until the end of the war in November 1918.

The task force reached the Åland Islands on 5 March, where they encountered the Swedish coastal defense ships HSwMS Sverige, Thor, and Oscar II.

Negotiations ensued, which resulted in the landing of the German troops on Åland on 7 March; Westfalen then returned to Danzig, where Posen was stationed.

[40] On 31 March Posen and Westfalen left Danzig; the ships arrived at Russarö, which was the outer defense for Hanko, by 3 April.

[24] On 11 August 1918, Posen, Westfalen, Kaiser, and Kaiserin sortied from Wilhelmshaven to support torpedo boats on patrol off Terschelling.

[40] On 2 October, Posen moved out into the outer roadsteads of the Jade to provide cover for the returning U-boats of the Flanders Flotilla.

The operation was intended to inflict as much damage as possible on the British navy, in order to retain a better bargaining position for Germany, whatever the cost to the fleet.

[24] On 11 November 1918, the Armistice took effect; according to its terms, eleven battleships and five battlecruisers were to be interned in Scapa Flow for the duration of negotiations for the peace treaty.