In due course I shall attempt to show the immediate connexion that exists between control of the surface and control of the subsurface; this narrative will disclose, indeed, that the nation which possesses the first also potentially possesses the second. In the early spring of 1917, however, this principle was not effective, so far as merchant shipping was concerned. Germany's purpose in adopting the ruthless submarine warfare was, of course, the one which I have indicated: to deprive the Allied armies in the field, and their civilian populations, of these supplies from overseas which were essential to victory. Nature had been kind to this German programme when she created the British Isles. Indeed this tight little kingdom and the waters which surround it provided an ideal field for operations of this character. For purposes of contrast, let us consider our own geographical situation. A glance at the map discloses that it would be almost impossible to blockade the United States with submarines. In the first place, the operation of submarines more than three thousand miles from their bases would present almost insuperable difficulties. That Germany could send an occasional submarine to our coasts she demonstrated in the war, but it would be hardly possible to maintain anything like a regular and persistent campaign. Even if she could have kept a force constantly engaged in our waters, other natural difficulties would have defeated their most determined efforts. The trade routes approach our Atlantic sea-coast in the shape of a fan, of which different sticks point to such ports as Boston, New York, Philadelphia, Norfolk, and the ports of the Gulf of Mexico. To destroy shipping to American ports it would be necessary for the enemy to cover all these routes with submarines, a project which is so vast that it is hardly worth the trial. In addition we have numerous Pacific ports to which we could divert shipping in case our enemy should attempt to blockade us on the Atlantic coast; our splendid system of transcontinental railroads would make internal distribution not a particularly difficult matter. Above all such considerations, of course, is the fact that the United States is an industrial and agricultural entity, self-supporting and self-feeding, and, therefore, it could not be starved into surrender even though the enemy should surmount these practically insuperable obstacles to a submarine blockade. But the situation of the British Isles is entirely different. They obtain from overseas the larger part of their food and a considerable part of their raw materials, and in April of 1917, according to reliable statements made at that time, England had enough food on hand for only six weeks or two months. The trade routes over which these supplies came made the submarine blockade a comparatively simple matter. Instead of the sticks of a fan, the comparison which I have suggested with our own coast, we now have to deal with the neck of a bottle.