Such was the atmosphere of gloom which prevailed in Allied councils in April, 1917; yet one year later the naval situation had completely changed. The reasons for that change have been set forth in the preceding pages. In that brief twelve months the relative position of the submarine had undergone a marked transformation. Instead of being usually the pursuer it was now often the pursued. Instead of sailing jauntily upon the high seas, sinking helpless merchantmen almost at will, it was half-heartedly lying in wait along the coasts, seeking its victims in the vessels of dispersed convoys. If it attempted to push out to sea, and attack a convoy, escorting destroyers were likely to deliver one of their dangerous attacks; if it sought the shallower coastal waters, a fleet of yachts, sloops, and subchasers was constantly ready to assail it with dozens of depth charges. An attempt to pass through the Straits of Dover meant almost inevitable destruction by mines; an attempt to escape into the ocean by the northern passage involved the momentary dread of a similar end or the hazard of navigating the difficult Pentland Firth. In most of the narrow passages Allied submarines lay constantly in wait with their torpedoes; a great fleet of airplanes and dirigibles was always circling above ready to rain a shower of bombs upon the under-water foe. Already the ocean floor about the British Isles held not far from 200 sunken submarines, with most of their crews, amounting to at least 4,000 men, whose deaths involved perhaps the most hideous tragedies of the war. Bad as was this situation, it was nothing compared with what it would become a few months or a year later. American and British shipyards were turning out anti-submarine craft with great rapidity; the industries of America, with their enormous output of steel, had been enlisted in the anti-submarine campaign. The American and British shipbuilding facilities were neutralizing the German campaign in two ways: they were not only constructing war vessels on a scale which would soon drive all the German submarines from the sea, but they were building merchant tonnage so rapidly that, in March, 1918, more new tonnage was launched than was being destroyed. Thus by this time the Teutonic hopes of ending the war by the submarine had utterly collapsed; if the Germans were to win the war at all, or even to obtain a peace which would not be disastrous, some other programme must be adopted and adopted quickly.