The decision of the German government to launch a campaign of unrestricted submarine warfare in the waters around the British Isles in January 1917 was arguably the turning point of the First World War and certainly one of the main causes of Germany's collapse and defeat in 1918. It has been described in previous literature as the Reich Chancellor Theobald von Bethmann Hollweg's ‘darkest hour’ and as a ‘literal capitulation of political authority before the military in the most crucial issue of the entire [war]’. Alternatively, it has been portrayed as a desperate gamble determined by the ‘exorbitant war aims’ of German industry and agriculture; as the last chance to ‘repay’ London for its ‘starvation blockade’ of Germany; as a propaganda exercise designed to lift morale and combat ‘war weariness’ during the ‘turnip winter’ of 1916/17; and even as part of the ‘logic of total war … in both the material and moral senses’. But what role did Kaiser Wilhelm II play personally in the coming of unrestricted submarine warfare? How far did he share the optimistic assessment of his naval advisers that England would be brought to its knees within six months, as well as the popular desire for revenge against ‘Perfidious Albion’?