 On 16 August 1915, Posen and Nassau led a second attempt to breach the defenses of the gulf, with Posen as Admiral Schmidt's flagship. The two dreadnoughts were accompanied by 4 light cruisers and 31 torpedo boats. On the first day of the assault the Germans broke through the Russian forces, but two German light craft — the minesweeper T46 and the destroyer V99 — were sunk. Posen and Nassau engaged a pair of Russian gunboats, Sivuch and Korietz. Sivuch was sunk that day and Korietz was severely damaged; the ship managed to limp away but had to be scuttled the following day. On the 17th, Posen and Nassau engaged Slava at long range; they scored three hits on the Russian ship and forced her to return to port. By 19 August, the Russian minefields had been cleared and the flotilla entered the Gulf. Reports of Allied submarines in the area prompted the Germans to call off the operation the following day. Admiral Hipper later remarked, "To keep valuable ships for a considerable time in a limited area in which enemy submarines were increasingly active, with the corresponding risk of damage and loss, was to indulge in a gamble out of all proportion to the advantage to be derived from the occupation of the Gulf before the capture of Riga from the land side." In fact, the battlecruiser Moltke had been torpedoed that morning. On 21 August, Schmidt had his flag hauled down from Posen and disbanded the special unit.
