From Friedman’s ‘Fighting the Great War at Sea’
The High Seas Fleet sortied again early in November 1916 to cover the recovery of U 20 which had gone aground north of Bobjerg. This time the battleships Grosser Kurfurst and Kronprinz were both torpedoed by the British submarine J 1 at the unusually long range of 4,000 yards (two hits for four torpedoes fired). Both ships managed to remain in formation but needed extensive repairs.
Kronprinz was ready 6 December 1916 and Grosser Kurfurst 10 February 1917
What damage did J 1 do?