Despite the relative calm on land, on the high seas, the war was very real. Within a few hours of the declaration of war, the British liner was torpedoed off the Hebrides with the loss of 112 lives in what was to be the beginning of the long-running Battle of the Atlantic. On 4 September, the Allies announced a blockade of Germany to prevent her importing food and raw materials to sustain her war effort; the Germans immediately declared a counter-blockade while Soviet Union helped Germany with supplies bypassing the blockade. RAF Bomber Command, Britain's principal offensive arm, was also heavily engaged, but found that daylight bombing caused little damage and cost insupportable losses (e.g., 12 out of 22 Wellington bombers were shot down in an air battle over the Wilhelmshaven naval base on 18 December 1939.)