I have pointed out above that "submarines cannot fight submarines," because they cannot see or locate each other. It is this very thing which will enable the cargo-carrying submarine to evade the military submarine. They are also able to evade all surface craft, either friend or foe. Captain Paul Koenig, of the _Deutschland_, told me that most of his journey in the _Deutschland_ was upon the surface. He stated that her low visibility enabled him to see all approaching ships before they could see her, and that it was only necessary for him to submerge and rest until the surface ship had passed on her way. The tactics of the larger cargo-carrying submarines would be the same. They need not have much radius of action when submerged; all they need to do is to hide until the danger has passed. If desired, however, their radius of submerged action may be increased to equal or largely exceed that of a military submarine, but this would unnecessarily increase their cost of construction; otherwise the cost of building such vessels should not exceed twenty-five per cent. more than the cost of constructing a first-class surface ship. Now I have prepared a few diagrams showing the advantage of various types of vessels in evading the submarine, and of these I shall treat immediately, as they illustrate the points of my contention perfectly. There was a time when everybody thought the earth was flat, but now I believe it is generally conceded that it is round. Every one knows that when the sun or moon sinks beneath the horizon it cannot be seen, neither can anything else which is below the horizon, so if the horizon intervenes between two distant observers they cannot see each other. Now by referring to our text-books we find that if an observer is stationed at a height of fifteen feet above the surface of the sea the horizon is five and one-eighths miles distant, so that if there were another observer stationed on the other side of the horizon at the same distance and height from the surface of the sea they could not see each other, as the surface of the earth or sea, being round, would stand up like a hill between them. [Illustration: THE "DEUTSCHLAND" By Courtesy of Motorship The "Deutschland" was the first submarine cargo-carrier to cross the Atlantic Ocean. She was under the command of Captain Paul Koenig and proved the practicability of running the English blockade four times before war between Germany and the United States caused her owners to discontinue her sailings. Had war not come between the two countries, her German owners would undoubtedly have had submarine cargo-carrying vessels making weekly sailings between the United States and Germany.] The diagram shown herewith shows the distance of horizon in miles from 0 to two hundred feet elevation above the surface of the water.