The two ships were re-mobilized after the outbreak of World War I in August 1914.
Prinz Adalbert was initially assigned to the IV Scouting Group, and alternated between the North and Baltic Seas for various operations, including cruising with the fleet during the Raid on Yarmouth in early November.
Friedrich Carl was sent to the Cruiser Division of the Baltic Sea commanded by Konteradmiral (Rear Admiral) Ehler Behring, where she served as his flagship.
The division was based in Neufahrwasser in Danzig.
Behring was ordered to attack the Russian port of Libau, which was believed to be acting as a staging area for British submarines.
On 17 November, while steaming to Libau, Friedrich Carl struck a pair of Russian naval mines off Memel.
The ship's crew managed to keep the cruiser afloat long enough to allow nearby vessels to take off the entire crew; only seven men were killed in the attack.
The operation proceeded as planned, however, and several blockships were sunk in the harbor entrance.

After the sinking of Friedrich Carl, Prinz Adalbert was transferred to the Cruiser Division and Behring shifted his flag to the vessel.
The ship conducted several operations against Russian forces in the southern Baltic in the first half of 1915, including bombardments of Libau and supporting minelayers around the Gulf of Riga.
She ran aground off Steinort in January but was able to free herself.
After repairs were completed, she returned to active duty in March.
In May, she supported the German Army attack that captured Libau.
On 1 July 1915, the ship sortied to reinforce a German minelaying operation that had come under attack by a Russian cruiser flotilla.
While en route with the armored cruiser Prinz Heinrich, Prinz Adalbert was torpedoed by the British submarine E9.
The damage was severe, though the cruiser was able to return to Kiel for repairs.

Repairs were finally completed by September 1915.
She took part in a sortie into the Gulf of Finland toward the end of the month that resulted in no action.
On 23 October, Prinz Adalbert was steaming some 20 miles west of Libau in company with a pair of destroyers when she was intercepted by the submarine E8.
E8 fired a spread of torpedoes at a range of approximately 1,200 meters (3,900 ft), which detonated the ship's ammunition magazine.
The explosion destroyed the ship, which sank immediately with the loss of 672 crew.
There were only three survivors.
The sinking was the greatest single loss of life for the German Baltic forces for the duration of the war.
The two ships were re-mobilized after the outbreak of World War I in August 1914. Prinz Adalbert was initially assigned to the IV Scouting Group, and alternated between the North and Baltic Seas for various operations, including cruising with the fleet during the Raid on Yarmouth in early November. Friedrich Carl was sent to the Cruiser Division of the Baltic Sea commanded by Konteradmiral (Rear Admiral) Ehler Behring, where she served as his flagship. The division was based in Neufahrwasser in Danzig. Behring was ordered to attack the Russian port of Libau, which was believed to be acting as a staging area for British submarines. On 17 November, while steaming to Libau, Friedrich Carl struck a pair of Russian naval mines off Memel. The ship's crew managed to keep the cruiser afloat long enough to allow nearby vessels to take off the entire crew; only seven men were killed in the attack. The operation proceeded as planned, however, and several blockships were sunk in the harbor entrance.
After the sinking of Friedrich Carl, Prinz Adalbert was transferred to the Cruiser Division and Behring shifted his flag to the vessel. The ship conducted several operations against Russian forces in the southern Baltic in the first half of 1915, including bombardments of Libau and supporting minelayers around the Gulf of Riga. She ran aground off Steinort in January but was able to free herself. After repairs were completed, she returned to active duty in March. In May, she supported the German Army attack that captured Libau. On 1 July 1915, the ship sortied to reinforce a German minelaying operation that had come under attack by a Russian cruiser flotilla. While en route with the armored cruiser Prinz Heinrich, Prinz Adalbert was torpedoed by the British submarine E9. The damage was severe, though the cruiser was able to return to Kiel for repairs.
Repairs were finally completed by September 1915. She took part in a sortie into the Gulf of Finland toward the end of the month that resulted in no action. On 23 October, Prinz Adalbert was steaming some 20 miles west of Libau in company with a pair of destroyers when she was intercepted by the submarine E8. E8 fired a spread of torpedoes at a range of approximately 1,200 meters (3,900 ft), which detonated the ship's ammunition magazine. The explosion destroyed the ship, which sank immediately with the loss of 672 crew. There were only three survivors. The sinking was the greatest single loss of life for the German Baltic forces for the duration of the war.
Prinz Adalbert-class cruiser