 By 1916 , these raiding forces were causing serious concern in the Admiralty as the proximity of Bruges to the British coast , to the troopship lanes across the English Channel and for the U @-@ boats , to the Western Approaches ; the heaviest shipping lanes in the World at the time . In the late spring of 1915 , Admiral Reginald <unk> had attempted without success to destroy the lock gates at Ostend with monitors . This effort failed , and Bruges became increasingly important in the Atlantic Campaign , which reached its height in 1917 . By early 1918 , the Admiralty was seeking ever more radical solutions to the problems raised by unrestricted submarine warfare , including instructing the " Allied Naval and Marine Forces " department to plan attacks on U @-@ boat bases in Belgium . 
