Karlsruhe was one of three Königsberg-class cruisers built for the Kriegsmarine in the mid-1920s, the first modern light cruisers built after WWI. Named after the city of Karlsruhe, she was laid down on 27th July 1926 in Kiel and commissioned on 6th November 1929. She was armed with nine 15 cm cannons in three triple turrets, with one forward and two superfiring aft, the rearmost being offset. Her anti-aircraft armament consisted of a pair of 8.8 cm guns in single mounts. Karlsruhe was also equipped with four triple 533 mm torpedo launchers amidships, with a total of 24 torpedoes. After entering service, she was assigned to training ship duties. Between September 1934 and 1935, her commanding officer was Günther Lütjens, who later became captain of the Bismarck. In 1935, Karlsruhe underwent a refit that added a catapult for a floatplane. In 1936, she was damaged by a storm while on a training cruise in the Pacific Ocean, her hull revealing structural weaknesses in the welded plating. She was temporarily repaired in San Diego before returning to Germany, where she underwent permanent repairs and a refit during which her AA guns were strengthened. Afterwards, she participated in non-intervention patrols during the Spanish Civil War. In 1938, her AA armament was further enhanced.
On 8th April 1940, she departed Bremerhaven with embarked troops for the invasion of Norway. A day later, the force entered Kristiansand and came under fire from Norwegian coastal guns at the Odderøya Fortress, which Karlsruhe engaged for about two hours before the fort surrendered and she landed her troops. During her withdrawal, she was spotted by the British submarine HMS Truant, which fired a spread of torpedoes at the ships. The crew sighted the torpedoes and attempted to evade them, but one struck Karlsruhe. The flooding disabled her engines and cut power to some of the pumps. The captain ordered the ship to be abandoned two hours after the attack, and the torpedo boat Greif took off her crew and scuttled Karlsruhe.
Karlsruhe was introduced in Update 2.9 "Direct Hit". Her playstyle is essentially similar to that of her sister Köln and her improved Leipzig-class successors. The Karlsruhe possesses impressive firepower, as her main guns can fire up to 12 rounds per minute; however, the ship itself—and particularly the magazines—are lightly protected by a 50 mm belt of armour and are located above the waterline, making them vulnerable to enemy fire. Her anti-aircraft suite consists of three pairs of 10.5 cm cannons using HE-TF shells or APHE against enemy vessels, while close-range protection is provided by four dual-mounted 3.7 cm SK C/30 cannons and eight single-mounted 2 cm/65 C/30 cannons.
