But while we recognize the fact that the convoy preserved our communications and so made possible the continuation of the war, we must not overlook a vitally important element in its success. In describing the work of the destroyer, which was the protecting arm of the convoy, I have said nothing about the forces that really laid the whole foundation of the anti-submarine campaign. All the time that these destroyers were fighting off the submarines the power that made possible their operations was cruising quietly in the North Sea, doing its work so inconspicuously that the world was hardly aware of its existence. For back of all these operations lay the mighty force of the Grand Fleet. Admiral Beatty's dreadnoughts and battle cruisers, which were afterward supplemented by a fine squadron of American ships, kept the German surface vessels penned in their harbours and in this way left the ocean free for the operations of the Allied surface craft. I have already said that, in April, 1917, the Allied navies, while they controlled the surface of the water, did not control the subsurface, which at that time was practically at the disposition of the Germans. Yet the determining fact, as we were now to learn, was that this control of the surface was to give us the control of the subsurface also. Only the fact that the battleships kept the German fleet at bay made it possible for the destroyers and other surface craft to do their beneficent work. In an open sea battle their surface navies would have disposed of the German fleet; but let us suppose for a moment that an earthquake, or some other great natural disturbance, had engulfed the British fleet at Scapa Flow. The world would then have been at Germany's mercy and all the destroyers the Allies could have put upon the sea would have availed them nothing, for the German battleships and battle cruisers could have sunk them or driven them into their ports. Then Allied commerce would have been the prey, not only of the submarines, which could have operated with the utmost freedom, but of the German surface craft as well. In a few weeks the British food supplies would have been exhausted. There would have been an early end to the soldiers and munitions which Britain was constantly sending to France. The United States could have sent no forces to the Western Front and the result would have been the surrender which the Allies themselves, in the spring of 1917, regarded as not a remote possibility. America would then have been compelled to face the German power alone, and to face it long before we had had an opportunity of assembling our resources and of equipping our armies. The world was preserved from all these calamities because the destroyer and the convoy solved the problem of the submarine and because back of these agencies of victory lay Admiral Beatty's squadrons, holding at arm's length the German surface ships while these comparatively fragile craft were saving the liberties of the world.