the Allies in the spring of 1917, was the undisputed mistress of the seas. Had the German submarine campaign continued to succeed at this rate, the United States could not have transported its army to France, and the food and materials which we were sending to Europe, and which were essential to winning the war, could never have crossed the ocean.

That is to say, complete control of the subsurface by Germany would have turned against England the blockade, the very power with which she had planned to reduce the German Empire. Instead of isolating Germany from the rest of the world, she would herself be isolated.

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. The trade routes to our Atlantic coast spread out, as they approach our ports; on the other hand, the trade routes to Great Britain converge almost to a point. The far-flung steamship lanes which bring Britain her food and raw materials from half a dozen continents focus in the Irish Sea and the English Channel. To cut the communications of Great Britain, therefore, the submarines do not have to patrol two or three thousand miles of sea-coast, as would be necessary in the case of the United States; they merely need to hover around the extremely restricted waters west and south of Ireland.

This was precisely the area which the Germans had selected for their main field of activity. It was here that their so-called U-boats were operating with the most deadly effect; these waters constituted their happy hunting grounds, for here came the great cargo ships, with food and supplies from America, which were bound for Liverpool and the great Channel ports. The submarines that did destruction in this region were the type that have gained universal fame as the U-boats. There were other types, which I shall describe, but the U-boats were the main reliance of the German navy; they were fairly large vessels, of about 800 tons, and carried from eight to twelve torpedoes and enough fuel and supplies to keep the sea for three or four weeks. And here let me correct one universal misapprehension. These U-boats did not have bases off the Irish and Spanish coasts, as most people still believe. Such bases would have been of no particular use to them. The cruising period of a submarine did not depend, as is the prevailing impression, upon its supply of fuel oil and food, for almost any under-water boat was able to carry enough of these essential materials for a practically indefinite period; the average U-boat, moreover, could easily make the voyage across the Atlantic and back. The cruising period depended upon its supply of torpedoes. A submarine returned to its base only after it had exhausted its supply of these destructive missiles; if it should shoot them all in twenty-four hours, then a single day would end that particular cruise; if the torpedoes lasted a month, then the submarine stayed out for that length of time. For these reasons bases on the Irish coast would have been useful only in case they could replenish the torpedoes, and this was obviously an impossibility. No, there was not the slightest mystery concerning the bases of the U-boats. When the Germans captured the city of Bruges in Belgium they transformed it into a headquarters for submarines; here many of the U-boats were assembled, and here facilities were provided for docking, repairing, and supplying them. Bruges was thus one of the main headquarters for the destructive campaign which was waged against British commerce. Bruges itself is an inland town, but from it two canals extend, one to Ostend and the other to Zeebrugge, and in this way the interior submarine base formed the apex of a triangle. It was by way of these canals that the U-boats reached the open sea.

Once in the English Channel, the submarines had their choice of two routes to the hunting grounds off the west and south of Ireland. A large number made the apparently unnecessarily long detour across the North Sea and around Scotland, going through the Fair Island Passage, between the Orkney and the Shetland islands, along the Hebrides, where they sometimes made a landfall, and so around the west coast of Ireland. This looks like a long and difficult trip, yet the time was not entirely wasted, for the U-boats, as the map of sinkings shows, usually destroyed several vessels on the way to their favourite hunting grounds. But there was another and shorter route to this area available to the U-boats. And here I must correct another widely prevailing misapprehension. While the war was going on many accounts were published in the newspapers describing the barrage across the English Channel, from Dover to Calais, and the belief was general that this barrier kept the U-boats from passing through. Unfortunately this was not the case. The surface boats did succeed in transporting almost at will troops and supplies across this narrow passage-way; but the mines, nets, and other obstructions that were intended to prevent