"Mars" was operated by the Neptun Line. She had a crew of 38 and accommodation for twelve passengers. She was requisitioned in 1940 by the Kriegsmarine, but was returned to Neptun Line later that year. She was requisitioned again in 1942. and converted to a hospital ship for military use. On 13 December 1943, "Mars" was severely damaged in an air raid on Bremen by the United States Eighth Air Force. She assisted in the evacuation of German citizens from Königsberg and Pillau. Between January and April 1945, she carried 20,000 people. "Mars" was probably the last major ship to leave Pillau for Copenhagen.