Her last patrol began from Tees on 27 December 1917, leaving with the submarine and the destroyer for the Kattegat. She was ordered to start her voyage back on 3 January 1918 or possibly 48 hours later, returning to Tees on or around 6 January 1918. She did not return and was never heard from again. She was officially declared missing on 14 January 1918. The cause remains unknown, but she was found with depth rudders pointing towards the surface, which suggests that the men aboard were trying to get to the surface. Therefore, it is thought that a technical error led to the sinking. There is no evidence on the wreck of it being hit by torpedoes or mines.*'Submarine losses 1904 to present day' - Royal Navy Submarine Museum
