The Royal Navy had blockaded Germany at the start of the First World War; the UK had declared the North Sea a war zone in the autumn of 1914 and mined the approaches. In the spring of 1915, all food imports for Germany were declared contraband. RMS "Lusitania" left New York for Britain on 1 May 1915 when German submarine warfare was intensifying in the Atlantic. Germany had declared the seas around the United Kingdom a war zone, and the German embassy in the United States had placed fifty newspaper advertisements warning people of the dangers of sailing on "Lusitania". Objections were made by the British that threatening to torpedo all ships indiscriminately was wrong, whether it was announced in advance or not.