 Markgraf struck a pair of mines in quick succession while in the <unk> Strait and took in 260 metric tons ( 260 long tons ; 290 short tons ) of water . The ship continued on to Kiel via <unk> in Danzig ; she then went on to Wilhelmshaven , where the mine damage was repaired . The work was completed at the Imperial Dockyard from 6 to 23 November . After repairs were completed , Markgraf returned to guard duty in the North Sea . She missed an attempted raid on a British convoy on 23 – 25 April 1918 , as she was in dock in Kiel from 15 March to 5 May for the installation of a new foremast . 
