part of its area exposed to the danger of ramming. The mere fact that its torpedo tubes are placed in the bow and stern makes it necessary for the submarine, if it wishes to attack in the fashion described, to turn almost at right angles to the course of the convoy, and to manoeuvre into a favourable position from which to discharge its missile--a procedure so altogether hazardous that it almost never attempts it. With certain reservations, which it is hardly necessary to explain in detail at this point, it may be taken at least as a general rule that the sides of the convoy not only furnish the U-boats much the best chance to torpedo ships, but also subject them to the least danger; and this is the reason why, in the recent war, the destroyers were usually concentrated at these points. I have already compared the convoy system to a great aggregation of railroads. This comparison holds good of its operation after it had entered the infested zone. Indeed the very terminology of our railroad men was used. Every convoy nearly followed one of two main routes, known at convoy headquarters as the two "trunk lines." The trunk line which reached the west coast of England usually passed north of Ireland through the North Channel and down the Irish Sea to Liverpool. Under certain conditions these convoys passed south of Ireland and thence up the Irish Sea. The convoys to the east coast took a trunk line that passed up the English Channel. Practically all shipping from the United States to Great Britain and France took one of these trunk lines. But, like our railroad systems, each of these main routes had branch lines. Thus shipping destined for French ports took the southern route until off the entrance to the English Channel; here it abandoned the main line and took a branch route to Brest, Bordeaux, Nantes, and other French ports. In the Channel likewise several "single-track" branches went to various English ports, such as Plymouth, Portsmouth, Southampton, and the like. The whole gigantic enterprise flowed with a precision and a regularity which I think it is hardly likely that any other transportation system has ever achieved. IV A description of a few actual convoys, and the experiences of our destroyers with them, will perhaps best make clear the nature of the mechanism which protected the world's shipping. For this purpose I have selected typical instances which illustrate the every-day routine experiences of escorting destroyers, and other experiences in which their work was more spectacular.