These three leading classes of vessels, with their functions, armaments, and tactics of the single ship, as described, performed in their day and during the great maritime contests of two centuries all the duties that at any time can be required of a maritime fighting organization. By them the control of the sea in the largest sense was disputed and was determined; by them commerce was attacked, and by them it was protected. They themselves have passed away, but the military factors remain the same. The mastery of the sea and the control of its commerce—of which blockade is but a special case—are now and must remain always the chief ends of maritime war. The ends continuing the same, the grand disposition of navies—their strategy—reposes upon the same principles that it ever did. Similarly, while the changes in the characteristics of ships will cause the individual vessel to be fought in manners different from its predecessors, the handling of masses of ships in battle—fleet tactics—must proceed on the same general principles as of old. The centre and the two extremities of all orders are always the points of danger; concentration upon one or two of the three, however effected, must be always the principle of action. These things, which cannot vary, form, therefore, no part of a paper which deals with changes. THEY HAD THEIR BREAK-DOWNS THEN, TOO There should be added for the general public the caution that the difficulties, the imperfections, and the frequent halting state of ships-of-war in commission for sea service at the present day are no new things. To the naval historian familiar with the correspondence of the past they are the inevitable attendants of all government action, wherein the most economical methods are always dominated, historically, by considerations of expediency which are political in character. The necessity of keeping the public in good-humor, and of not laying open points upon which opposition can enlarge, induces apparent economies, which sacrifice not only economy, but the best results. This is a great evil, as yet apparently inseparable from public enterprises as distinguished from private ones. If any one supposes that the ships with which Great Britain overthrew Napoleon, and with which Nelson and his contemporaries won their as yet unparalleled victories, were always or generally in good material condition, he is greatly mistaken. What is different in our day, apparently, is a tendency in ships to rely for their repairs and material efficiency more upon dock-yards and workshops than upon their own resources, a disposition also to be unduly discouraged by imperfections in the motive enginery. War will correct this or war will fail. In maintaining efficiency while keeping the sea, quite as much as in fighting skill, lay the supreme excellence of officers like Nelson and Jervis. Men now ought to appreciate better than they do what difficulties of this sort seamen underwent a hundred