=High Speed.=--Speed is better than no defence, but no one would consider building twenty-five-knot freighters. The cost would be far out of proportion to the service. So long as U-boats do not betray their presence, a fast vessel is almost as liable as a slower one of less freeboard or lower top hamper. One can never tell where the submarine may be lurking, and her capacity to harm is determined by her ability to locate her prey. There are three means available to her to locate her target: first, her own sight; second, her sound-detecting devices; third, by wireless directions given to her by others who may advise her of the vessel's position. Her own sight is the best and usual means for locating her target. The above diagrams show that the largest and fastest ships can be located at much greater distances than the low visibility ships, and that the area of visibility becomes the area of danger, which is practically ten times greater in an expensive, large, high-speed liner over that of the comparatively low-cost cargo-carrying submarine. [Illustration: BRITISH SUBMARINE NO. 3 PASSING NELSON'S OLD FLAGSHIP "VICTORY" This submarine is of the Holland type, similar to the U. S. "Adder" and "Moccasin." This illustration shows the radical change made in naval warfare in one hundred years.] One should not imagine that the Germans are carrying on this campaign at random. It is well organized and systematic. Each vessel that comes in sight of a submarine is a marked vessel, and even if she is the fastest vessel afloat, she may speed unwittingly into a trap set for her by wireless. So long as she cannot disappear she has no real ability to elude. On the other hand, the cargo-carrying submarine of low speed has both these advantages: she has low visibility and the capability of disappearance. She may become invulnerable when danger threatens. She has all of the qualities possessed by her enemies. She may beat them at their own game. Vessels of the ordinary type will suffice in no way to meet the great problem presented by the U-boats. The cargo submarine, however, readily meets all the needs of the situation. This is the sole method of which I am cognizant by means of which a submarine blockade and the destruction of cargo-carrying vessels can be overcome with safety and with certainty. I have expected the Germans would blockade our own ports, as it is easily possible for them to do so; I believe the reason they have not done so thus far is because of political reasons, as it would undoubtedly be to their advantage to have our trade after the war, which they might not have if they arouse our hatred any more than they already have. CHAPTER VII THE SUBMARINE IN TIMES OF PEACE