SMS Frithjof was the third vessel of the six-member Siegfried class of coastal defense ships (Küstenpanzerschiffe) built for the German Imperial Navy. Her sister ships were Siegfried, Beowulf, Heimdall, Hildebrand, and Hagen. Frithjof was built by the AG Weser shipyard between 1890 and 1893, and was armed with a main battery of three guns. She served in the German fleet throughout the 1890s and was rebuilt in 1900–1902. She served in the VI Battle Squadron after the outbreak of World War I in August 1914, but saw no action. Frithjof was demobilized in 1915 and used as a barracks ship thereafter. She was rebuilt as a merchant ship in 1923 and served in this capacity until she was broken up for scrap in 1930.