On the 11 October 1917, German land and naval forces launched an amphibious assault, code named Operation Albion, on the islands of Saaremaa (Ösel), Hiiumaa (Dagö) and Muhu (Moon); they controlled the entrance to the Gulf of Riga. By the end of the month German forces had successfully overrun the islands forcing the Russians to abandon them with the loss of some 20,000 troops, 100 guns and the pre-dreadnought battleship "Slava". The capture of the islands opened a route for German naval forces into the Gulf of Finland threatening the city of Petrograd, a fact that contributed to the cessation of hostilities on the Eastern front.