Though nominally a neutral nation during the "Great War" of World War I (1914–1918), Norway was in the unenviable position of being dependent on the warring sides for its trade. Coal from Britain was needed to keep the country going, and Norway had thus to agree that each shipload of coal leaving Britain be matched with incoming Norwegian cargoes such as copper ore and fish. This attracted the attention of the opposing German Empire and its Imperial German Navy's numerous submarines.