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. "Hannover" then joined the battleship support for the battlecruisers that bombarded Scarborough, Hartlepool, and Whitby on 15–16 December 1914. During the operation, the German battle fleet of 12 dreadnoughts and eight pre-dreadnoughts came within of an isolated squadron of six British battleships. However, skirmishes between the rival destroyer screens in the darkness convinced the German fleet commander, "VAdm" Friedrich von Ingenohl, that the entire Grand Fleet was deployed before him. Under orders from Wilhelm II to avoid battle if victory was not certain, Ingenohl broke off the engagement and turned the battle fleet back towards Germany.