Late in June 1915 a number of enemy warships bombarded Windau with 9.4–in. guns, and also tried to effect a descent on the coast with a view to co-operating with the German army in Courland. The invasion project was entirely unsuccessful, and the naval forces were compelled to retire. The defence seems mainly to have been the work of torpedo-boats; no mention was made on either side of the presence of submarines. A similar attempt made three weeks before had robbed the Russians of the _Yenissei_, which fell a victim to a U-boat. According to reports furnished by commanders of Russian submarines, three of the enemy vessels were sunk or damaged by mines previously dropped by the wrecked vessel. Early in the following month Russian naval forces came across two enemy light cruisers and destroyers on outpost duty between Gothland and Windau. On this occasion the tables were turned, and the Germans lost a mine-layer. The _Albatross_, the ship in question, was so severely handled that she ran aground near Oestergarn, and became a total wreck, her consort, the _Augsburg_, managing to escape in the fog. While the Russian squadron continued its course northward, two cruisers, four destroyers, and a flotilla of U-boats joined battle, but speedily retreated after the armoured cruiser _Roon_ had been badly damaged. On being reinforced by a battle squadron, another attempt was made against the Russian vessels, including a spirited submarine attack on the _Rurik_. The latter was saved by a destroyer, which was reported to have sunk one of the hostile underwater craft. The 2nd July was a disastrous day for Germany in the Baltic. In addition to the _Albatross_ she lost a battleship of the _Pommern_ type at the hands of Commander Max K. Horton.[32] On the 30th, E 1 sank a large transport, despite a determined effort on the part of the latter to run down the attacking party. The next happening of importance from the point of view of the submarine war was a dramatic series of actions at the entrance of the Gulf of Riga in the succeeding August. These were carried out with the object of assisting Hindenburg’s land offensive in the direction of the great seaport of Riga, whose fall would open the road to Petrograd. The weather, mostly calm and foggy, was entirely favourable to the enemy, who slipped past the patrols and were able to sweep up many mines that barred further progress. In this dangerous operation it would have been nothing short of miraculous had the enemy escaped scot-free, and one or two vessels were destroyed. The Russian warships put up an excellent defence, with the result that the attempt to capture the old city of the Merchant-Venturers completely failed and the Gulf was evacuated.