The invasion force departed Bremerhaven early on 8 April 1940 with "Kapitän zur See" Friedrich Rieve aboard "Karlsruhe" commanding. When it arrived at Kristiansand, heavy fog covered the area, making the passage of the fjord outside the harbor very hazardous. As a result, the German ships had to wait until the morning of 9 April to begin the attack. As "Karlsruhe" entered the fjord, she came under heavy fire from the Norwegian coastal guns at Odderøya Fortress. The cruiser turned in the fjord to bring her full broadside into action; the artillery duel lasted for about two hours before heavy fog again covered the port, forcing both sides to cease fire. The Norwegians surrendered an hour later, and the German ships landed their embarked troops.