Passage: The eight I Squadron ships went into the Baltic on 22 February 1915 for unit training, which lasted until 13 March. Following their return to the North Sea, the ships participated in a series of uneventful fleet sorties on 29–30 March, 17–18 April, 21–22 April, 17–18 May, and 29–30 May. Thüringen and the rest of the fleet then remained in port until 4 August, when I Squadron returned to the Baltic for another round of training maneuvers. From there, the squadron was attached to the naval force that attempted to sweep the Gulf of Riga of Russian naval forces in August 1915. The assault force included the eight I Squadron battleships, the battlecruisers Von der Tann, Moltke, and Seydlitz, several light cruisers, 32 destroyers and 13 minesweepers. The plan called for channels to be swept in Russian minefields so that the Russian naval presence, which included the pre-dreadnought Slava, could be eliminated. The Germans would then lay minefields of their own to prevent Russian ships from returning to the Gulf. Thüringen and the majority of the other big ships of the High Seas Fleet remained outside the Gulf for the entirety of the operation. The dreadnoughts Nassau and Posen were detached on 16 August to escort the minesweepers and to destroy Slava, though they failed to sink the old battleship. After three days, the Russian minefields had been cleared, and the flotilla entered the Gulf on 19 August; reports of Allied submarines in the area prompted a German withdrawal from the Gulf the following day. By 26 August, I Squadron had returned to Wilhelmshaven.On 23–24 October, the High Seas Fleet undertook its last major offensive operation under the command of von Pohl, though it ended without contact with British forces. By January 1916 hepatic cancer had weakened von Pohl to the point where he was no longer able to carry out his duties, and he was replaced by Vice Admiral Reinhard Scheer in January. Scheer proposed a more aggressive policy designed to force a confrontation with the British Grand Fleet; he received...

Question: In what year had hapatic cancer weaken von Pohl?
1916