Germany's swift and successful occupation of France and the Low Countries gained control of the Channel coast. Grand Admiral Erich Raeder met Hitler on 21 May 1940 and raised the topic of invasion, but warned of the risks and expressed a preference for blockade by air, submarines and raiders. By the end of May, the "Kriegsmarine" had become even more opposed to invading Britain following its costly victory in Norway. Over half of the "Kriegsmarine" surface fleet had been either sunk or badly damaged in "Operation Weserübung", and his service was hopelessly outnumbered by the ships of the Royal Navy.