 In 1916 , the British planned to clear the German army from the Belgian coast to prevent them from using the coastal ports as bases from which to attack merchant ships and troop transports in the North Sea and English Channel . In January 1916 , General Sir Herbert Plumer recommended to Field Marshal Sir Douglas Haig the capture of Messines Ridge ( part of the southern arc of the Ypres Salient ) before an operation to capture the Gheluvelt plateau further north . 
