Jospeph Kuppers served as an assistant surgeon aboard the Kronprinz Wilhelm. This was an armed merchantman that went under the guise of Maria of Flensburg when in port and even had a dummy funnel which could be erected to further hide her true identity. The vessel was intended as either a raider or else as a decoy vessel to lure submarines into surfacing before attacking her.
Kuppers was captured to the east of the Danish mainland on 2 November 1917 when his ship was attacked by British destroyers. He was not interrogated by British naval intelligence because his injuries were so severe. He could not even give his date of birth. He was scheduled for repatriation to Germany in September 1918. He is subsequently recorded at a military hospital in Kiel, but whether he was a patient or member of staff is not entirely clear.
See article Josef Kuppers and Repatriation https://arts.leeds.ac.uk/kriegsgefangen/josef-kuppers-and-repatriation/