She saw major action at Jutland and frequently engaged British light forces, culminating in her being torpedoed by destroyers shortly after midnight.

The side belt armor was increased in height to improve the ships' resistance to enemy fire, and fuel oil was introduced as part of the propulsion system on an experimental basis.

Additional protection was provided by a curved armor deck that sloped downward at the sides of the ship and connected to the bottom edge of the belt.

After completing Fitting-out work, the ship was delivered to the navy on 14 January 1914, but her commissioning into active service was delayed until 5 February owing to a lack of manpower.

[2][4] Rostock then escorted Kaiser Wilhelm II aboard his yacht, Hohenzollern, during his annual summer cruise to Norwegian waters in July.

As Europe slid toward war, the German fleet sailed back to Germany on 27 July; after arriving in Kiel later that day, Rostock was assigned to guard the outer roadstead against an expected torpedo-boat attack by Russian forces, though it did not materialize.

The following day, Austria-Hungary declared war on Serbia over the assassination, and by 2 August, Germany had mobilized against Russia, in support of its Austro-Hungarian ally.

In accordance with the fleet's mobilization plan, Rostock was assigned as the flagship of Kapitän zur See (Captain at Sea) Johannes Hartog, the II Commander of Torpedo-boats.

[6] Rostock's first wartime operation came on 9 August, when she led I Torpedo-boat Flotilla on a sweep into the southern North Sea to determine the position of the British patrol line.

The attack on the English coast took place early the next morning, but Rostock and the main fleet was stationed well to the rear to provide distant support.

On the evening of 15 December, the German battle fleet of some twelve dreadnoughts and eight pre-dreadnoughts came to within 10 nautical miles (19 km; 12 mi) of an isolated squadron of six British battleships.

However, skirmishes between the rival torpedo boat and destroyer screens in the darkness convinced the German commander—Admiral Friedrich von Ingenohl—that he was faced with the entire Grand Fleet.

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

[9] Rostock joined the light cruisers of II Scouting Group on 3 January 1915 to conduct a mine-sweeping operation to the west of Amrun Bank.

[6] On 24 January, Rostock formed part of the support for Admiral Franz von Hipper's battlecruisers in I Scouting Group during a sortie to destroy British light forces known to be operating near the Dogger Bank.

The German group encountered five British battlecruisers, resulting in the Battle of Dogger Bank, during which the armored cruiser Blücher was sunk.

They returned to the North Sea, and Rostock resumed her role leading the torpedo-boat flotillas during a fleet sweep on 29–30 March that failed to locate any British vessels.

On 16 December, Rostock, II Scouting Group, and several torpedo boats sortied for a patrol in search of British merchant shipping in the Skagerrak and Kattegat between Denmark and Norway.

Another operation in the direction of Terschelling, this time in company with II Scouting Group, began on 25 March, but was cancelled the next day due to heavy seas.

The Germans failed to locate any British surface ships, but they did encounter the submarine HMS E31, which launched a torpedo at Rostock that missed.

The destroyers launched several torpedoes at the Germans, forcing Rostock and the other cruisers to turn away to avoid them; this pointed the ships directly at the battleships in I Battle Squadron.

Gunfire from Rostock and the battleships Westfalen and Rheinland smothered the British destroyer; although heavily damaged, she managed to limp back to port.

[15] Rostock was attacked by the destroyers Ambuscade and Contest; the two ships each fired a single torpedo at high-speed settings at a range of about 1,000 yd (910 m).

Scuttling charges had been set in the cruiser, but to ensure Rostock sank faster, the two destroyers fired a total of three torpedoes into the ship.