[Illustration: THE OPTION OFFERED TO THE GERMAN SUBMARINES This diagram explains why the American navy succeeded in transporting more than 2,000,000 American soldiers to France without loss because of submarines. The Atlantic was divided into two broad areas--shown by the shaded parts of the diagram. Through the northern area were sent practically all the merchant ships with supplies of food and materials for Europe. The southern area, extending roughly from the forty-fifth to the forty-ninth parallel, was used almost exclusively for troopships. The Germans could keep only eight or ten U-boats at the same time in the eastern Atlantic; they thus were forced to choose whether they should devote these boats to attacking mercantile or troop convoys. The text explains why, under these circumstances, they were compelled to use nearly all their forces against merchant ships and leave troop transports practically alone. Emery Walker Ltd. sc] Up to the present moment this narrative has been concerned chiefly with the northernmost of these two great sea pathways. Through this one to the north passed practically all the merchant shipping which was destined for the Allies. Consequently, as I have described, it was the great hunting ground of the German submarines. I have thus far had little to say of the Bay of Biscay section because, until 1918, there was comparatively little activity in that part of the ocean. For every ship which sailed through this bay I suppose that there were at least 100 which came through the Irish Sea and the English Channel. In my first report to the Department I described the principal scene of submarine activity as the area of the Atlantic reaching from the French island of Ushant--which lies just westward of Brest--to the tip of Scotland, and that remained the chief scene of hostilities to the end. Along much of the coastline south of Brest the waters were so shallow that the submarines could operate only with difficulty; it was a long distance from the German bases; the shipping consisted largely of coastal convoys; much of this was the coal trade from England; it is therefore not surprising that the Germans contented themselves with now and then planting mines off the most important harbours. Since our enemy was able to maintain only eight or ten U-boats in the Atlantic at one time it would have been sheer waste of energy to have stationed them off the western coast of France. They would have put in their time to little purpose, and meanwhile the ships and cargoes which they were above all ambitious to destroy would have been safely finding their way into British ports.