Supply problems and technical difficulties caused some delays. Planned additional minelaying excursions to complete the barrage were cancelled when the approaching end of hostilities was recognized upon completion of the thirteenth minelaying excursion on 26 October 1918. The design of the minefield meant there was a theoretical 66% chance of a surfaced U-boat triggering a mine and a 33% chance for a submerged U-boat. On the basis of the number of effective mines observed while sweeping the barrage, the actual odds were assessed at being closer to 20% for a surfaced U-boat and 10% for a submerged one. As the final mines were laid only a matter of days before the end of World War I, it is impossible to assess the success of the plan. Some contend the minefield was a major cause of the declining morale of the Imperial German Navy through the final months of the war, while others suggest Germany easily swept safe channels through the large, unguarded minefield.