which rage so frequently in the winter months in these northern waters. If the British navy had not succeeded in constructing an effective mine barrier across the English Channel, what was the likelihood that success would crown an effort to build a much greater obstruction in the far more difficult waters to the north? The one point which few understood at that time was that the mere building of the barrage would not in itself prevent the escape of submarines from the North Sea. Besides building such a barrage, it would be necessary to protect it with surface vessels. Otherwise German mine-sweepers could visit the scene, and sweep up enough of the obstruction to make a hole through which their submarines could pass. It is evident that, in a barrage extending 250 miles, it would not be difficult to find some place in which to conduct such sweeping operations; it is also clear that it would take a considerable number of patrolling vessels to watch such an extensive barrier and to interfere with such operations. Moreover, we could not send our mine-layers into the North Sea without destroyer escort; that is, it would be necessary to detach a considerable part of our forces to protect these ships while they were laying their mines. Those responsible for anti-submarine operations believed that in the spring and summer of 1917 it would have been unwise to detach these anti-submarine vessels from the area in which they were performing such indispensable service. The overwhelming fact was that we needed all the surface craft we could assemble for the convoy system. The destroyers which we had available for this purpose were entirely inadequate; to have diverted any of them for other duties would at that time have meant destruction to the Allied cause. The object of placing the barrage so far north was to increase the enemy's difficulty in attempting to sweep a passage through it and facilitate its defence by our forces. The impossibility of defending a mine barrier placed too far south was shown by experience in that area of the North Sea which was known as the "wet triangle." By April, 1917, the British had laid more than 30,000 mines in the Bight of Heligoland, and were then increasing these obstructions at the rate of 3,000 mines a month. Yet this vast explosive field did not prevent the Germans from sending their submarines to sea. The enemy sweepers were dragging out channels through the mine-fields almost as rapidly as the British were putting new fields down; we could not prevent this, because protecting vessels could not remain so near the German bases without losses from submarine attacks. Moreover, the Germans also laid mines in the same area in order to trap the British mine-layers; and these operations resulted in very considerable losses on each side. These impediments made the egress of a submarine a difficult and nerve-racking process; it sometimes required two or three days and the assistance of a dozen or so surface vessels to