This fact is so familiar that I insist upon it here only for the purpose of inviting attention to another fact which is not so apparent. Perhaps the greatest commonplace of the war, from the newspaper standpoint, was that the British fleet controlled the seas. This mere circumstance, as I have already said, was the reason why all students of history were firm in their belief that Britain could never be defeated. It was not until the spring of 1917 that we really awoke to the actual situation; it was not until I had spent several days in England that I made the all-important discovery, which was this--that Britain did _not_ control the seas. She still controlled the seas in the old Nelsonian sense; that is, her Grand Fleet successfully "contained" the German battle squadrons and kept them, for the greater part of the war, penned up in their German harbours. In the old days such a display of sea power would have easily won the war for the Allies. But that is not control of the seas in the modern sense; it is merely control of the _surface_ of the seas. Under modern methods of naval warfare sea control means far more than controlling the top of the water. For there is another type of ship, which sails stealthily under the waves, revealing its presence only at certain intervals, and capable of shooting a terrible weapon which can sink the proudest surface ship in a few minutes. The existence of this new type of warship makes control of the seas to-day a very different thing from what it was in Nelson's time. As long as such a warship can operate under the water almost at will--and this was the case in a considerable area of the ocean in the early part of 1917--it is ridiculous to say that any navy controls the seas. For this subsurface vessel, when used as successfully as it was used by the Germans in 1917, deprives the surface navy of that advantage which has proved most decisive in other wars. That is, the surface navy can no longer completely protect communications as it could protect them in Nelson's and Farragut's times. It no longer guarantees a belligerent its food, its munitions, its raw materials of manufacture and commerce, or the free movement of its troops. It is obviously absurd to say that a belligerent which was losing 800,000 or 900,000 tons of shipping a month, as was the case with 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.