By late 1914, on the Western Front, the Franco-British counter-offensive of the First Battle of the Marne had ended and the Belgians, British and French had suffered many casualties in the First Battle of Ypres in Flanders. The war of manoeuvre had ended and been replaced by trench warfare. The German Empire and Austria-Hungary closed the overland trade routes between Britain and France in the west and Russia in the east. The White Sea in the arctic north and the Sea of Okhotsk in the Far East were icebound in winter and distant from the Eastern Front; the Baltic Sea was blockaded by the "Kaiserliche Marine" (Imperial German Navy) and the entrance to the Black Sea through the Dardanelles was controlled by the Ottoman Empire. While the Ottomans remained neutral, supplies could still be sent to Russia through the Dardanelles but prior to the Ottoman entry into the war, the straits had been closed; in November the Ottomans began to mine the waterway.