The ferry Tannenberg was used for mine laying operations in the Baltic Sea until May 1940. In the following 6 monthes it served as a training ship for cadets until it was sent into the North Sea in preperation for Operation Seelöwe. After cancellation of this operation, the Tannenberg worked on the so called "Westwall" mine barriers in the North Sea. In mid 1941, the ship returend to the Baltic Sea and help to lay the mine fields in the eastern Baltic Sea.

On 09.07.1941, the ship run in a Swedish mine barrier near Öland at 56°15,5'N and 16°43,5'E and sunk. Together with the Tannenberg , the mine layers Hansestadt Danzig and Preußen were lost, too. Thwe wreck of the Tannenberg was scrapped in 1952.