The ships of her class were already outdated by the time they entered service, being inferior in size, armor, firepower, and speed to the revolutionary new British battleship HMS Dreadnought.

After the battle, which exposed the weakness of pre-dreadnoughts like Hannover, she and her three surviving sisters were removed from active duty with the fleet to serve as guard ships.

She served with the fleet for ten years, from 1921 to 1931, during which time she took part in several major overseas cruises to Spain and the Mediterranean Sea.

The passage of the Second Naval Law in 1900 under the direction of Vizeadmiral (VAdm—Vice Admiral) Alfred von Tirpitz secured funding for the construction of twenty new battleships over the next seventeen years.

[b] HHer offensive armament was rounded out with a secondary battery of fourteen 17 cm (6.7 in) SK L/40 guns mounted individually in casemates.

Her armored belt was 240 millimeters (9.4 in) thick in the central citadel, where it protected her magazines and machinery spaces, while thinner plating covered the ends of the hull.

The experiences of the Russo-Japanese War, then being fought, suggested that naval armor was too thin to protect against modern guns, and so the German designers increased the thickness of the main belt and the central citadel; this change was repeated in the three subsequent members of the class.

After completing fitting out, the ship was commissioned for sea trials on 1 October 1907, but they were interrupted so that Hannover could join the fleet exercises in the Skagerrak in November.

[10] She was assigned to II Battle Squadron of the High Seas Fleet, joining her sisters Deutschland and Pommern; she replaced the older battleship Brandenburg.

She then took Braunschweig's place as the deputy command flagship on 27 April, and KAdm Ehrhard Schmidt hoisted his flag aboard the ship that day.

After the autumn maneuvers, Souchon was relieved by Kapitän zur See (KzS – Captain at Sea) Franz Mauve [de] so he could be sent to command the Mediterranean Division.

[15] Following the outbreak of World War I, Hannover was tasked with guard duty in the Altenbruch roadstead at the mouth of the Elbe River during the period of mobilization for the rest of the fleet.

In late October, the ships were sent to Kiel to have modifications made to their underwater protection systems to make them more resistant to torpedoes and mines.

[14] During the operation, the German battle fleet of 12 dreadnoughts and eight pre-dreadnoughts came within 10 nmi (19 km; 12 mi) of an isolated squadron of six British battleships.

[16] Hannover put to sea during the Battle of Dogger Bank on 24 January 1915 to support the beleaguered German battlecruisers, but quickly returned to port.

KzS Gottfried von Dalwigk zu Lichtenfels replaced Mauve on 11 August, raising his flag aboard Hannover on the 20th.

During the fleet advance of 5–7 March 1916, Hannover and the rest of II Squadron remained in the German Bight, ready to sail in support.

[17] Admiral Reinhard Scheer, the commander of the German fleet, immediately planned another advance into the North Sea, but the damage to Seydlitz delayed the operation until the end of May.

[20] During the "Run to the North", Scheer ordered the fleet to pursue the retreating battleships of the British V Battle Squadron at top speed.

Mauve considered moving his ships to the rear of the line, astern of III Battle Squadron dreadnoughts, but decided against it when he realized the movement would interfere with the maneuvering of Admiral Franz von Hipper's battlecruisers.

[30] Late on the 31st, the fleet organized for the night voyage back to Germany; Deutschland, Pommern, and Hannover fell in behind König and the other dreadnoughts of III Battle Squadron towards the rear of the line.

Nassau was forced to fall out of line to avoid the sinking British ship, and an hour later rejoined the formation directly ahead of Hannover.

[38] 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.

[39] The German fleet reached Wilhelmshaven a few hours later, where the undamaged dreadnoughts of the Nassau and Helgoland classes took up defensive positions while the damaged ships and the survivors of II Squadron retreated within the harbor.

Now-KAdm Dalwigk zu Lichtenfels hauled down his flag on 30 November and a replacement was not appointed, though II Squadron remained in at least administrative existence until 15 August 1917.

The unit was based in Swinemünde, and at the time it also included the light cruiser Medusa, the survey ship Panther, and I Torpedo-boat Flotilla.

Hannover was damaged in the accident and water flooded the engine room, forcing her to return to Wilhelmshaven for repairs that lasted until February 1925.

At that time, the active German fleet consisted of Hannover, Braunschweig, the light cruiser Amazone, and II Torpedo-boat Flotilla.

She made stops in Vigo, Valencia, Messina, Athens, Argostolion, Palma de Mallorca, and Cádiz before arriving back in Wilhelmshaven on 18 June.

She participated in the autumn maneuvers that year, which concluded with a naval review for the outgoing fleet commander, VAdm Iwan Oldekop, on 11 September.