During the First World War, the British Army's most consistent German opponent was Crown Prince Rupprecht of Bavaria. Commanding more than a million men as a General, and then Field Marshal, in the Imperial German Army, he held off the attacks of the British Expeditionary Force under Sir John French and then Sir Douglas Haig for four long years. But Rupprecht was to lose not only the war, but his son and his throne. Haig's Enemy by Jonathan...