 Complete the following phrase:  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 2930 March, 1718 April, 2122 April, 1718 May, and 2930 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 , , 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 , 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 