cellular division of the hull for defense; the armor to keep out the enemy's shells, and the cellular division of the hull to prevent the admission of more water than can fill one water-tight compartment in case the ship is hit.

It must be admitted here that, at the present moment, torpedoes hold such large charges of explosive that the cellular division of ships does not adequately protect them. This means that a contest has been going on between torpedo-makers and naval constructors like the contest between armor-makers and gunmakers, and that just now the torpedo-makers are in the lead. For this reason a battleship needs other protection than that imparted by its cellular subdivision. This is given by its "torpedo defense battery" of minor guns of about 5-inch calibre.

By reason of the great vulnerability of all ships to attack below the water-line, the torpedo was invented and developed. In its original form, the torpedo was motionless in the water, either anchored to the ground, or floating on the surface, and was in fact what now is called a "mine." But forty-eight years ago an Englishman named Whitehead invented the automobile, auto-steering, torpedo, which still bears his name. This torpedo is used in all the navies, and is launched on its mission from battleships, battle cruisers, destroyers, submarines, and other craft of various kinds.

Most torpedoes are to be found in destroyers—long, fast, frail vessels, averaging about 700 tons displacement, that are intended to dash at enemy ships at night, or under other favorable conditions, launch their torpedoes, and hurry away. The torpedo is "a weapon of opportunity." It has had a long, slow fight for its existence; but its success during the present war has established it firmly in naval warfare.

The submarine has followed the destroyer, and some people think will supplant it; though its relatively slow speed prevents those dashes that are the destroyer's rôle. The submarine is, however, a kind of destroyer that is submersible, in which the necessities of submersibility preclude great speed. The submarine was designed to accomplish a clear and definite purpose—a secret under-water attack on an enemy's ship in the vicinity. It has succeeded so well in its limited mission that some intelligent people declare that we need submarines only—ignoring the fact that, even if submarines could successfully prevent actual invasion, they could not carry on operations at a distance from their base of supplies. It is true that submarines may be made so large that they can steam at great speed from place to place, as capital ships steam now, carry large supplies of fuel and food, house their crews hygienically, and need no "mother ship" or tender. But if submarines achieve such size, they will be more expensive to build and run than battleships—and will be, in fact, submersible battleships. In other words, the submarine cannot displace the battleship, but may be developed and evolved into a new and highly specialized type of battleship.

The necessity for operating at long distances from a base carries with it the necessity for supplying more fuel than even a battleship can carry; and this means that colliers must be provided. In most countries, the merchant service is so large that colliers can be taken from it, but in the United States no adequate merchant marine exists, and so it is found necessary to build navy colliers and have them in the fleet. The necessity for continuously supplying food and ammunition to the fleet necessitates supply ships and ammunition ships; but the problem of supplying food and ammunition is not so difficult as that of supplying fuel, for the reason that they are consumed more slowly.

In order to take care of the sick and wounded, and prevent them from hampering the activities of the well, hospital ships are needed. Hospital ships should, of course, be designed for that purpose before being constructed; but usually hospital ships were originally passenger ships, and were adapted to hospital uses later.

The menace of the destroyer—owing to the sea-worthiness which this type has now achieved, and to the great range which the torpedo has acquired—has brought about the necessity of providing external protection to the battleships; and this is supplied by a "screen" of cruisers and destroyers, whose duty is to keep enemy destroyers and (so far as is practicable) the submarines at a safe distance.

We now see why a fleet must be composed of various types of vessels. At the present moment, the battleship is the primary, or paramount type, the others secondary, because the battleship is the type that can exert the most force, stand the hardest punishment, steam the farthest in all kinds of weather, and in general, serve her country the best.

Of course, "battleship" is merely a name, and some think not a very good name, to indicate a ship that can take the part in battle that used to be taken by the "ship of the line." The reason for its primacy is fundamental: its displacement or total weight—the same reason that assured the primacy of the ship of the line. For displacement rules the waves; if "Britannia rules the waves," it is simply because Britannia has more displacement than any other Power.

The fleet needs to have a means of knowing where the enemy is, how many ships he has, what is their character, the direction in which they are steaming, and their speed. To accomplish this purpose, "scouts" are needed—fast ships, that can steam far in all kinds of weather and send wireless messages across great distances. So far as their scout duties go, such vessels need no guns whatever, and no torpedoes; but because the enemy will see the scout as soon as the scout sees the enemy, and because the enemy will try to drive away the scout by gun and torpedo fire, the scouts must be armed. And this necessity is reinforced by the necessity of driving off an enemy's scouts.

In foreign navies the need for getting information in defiance of an enemy's attempts to prevent it, and to drive off the armed scouts of an enemy, has been one of the prime reasons for developing "battle cruisers," that combine the speed of the destroyer with the long steaming radius of the battleship, a battery almost as strong, and a very considerable protection by armor.

The aeroplane and the air-ship are recent accessions to the list of fighting craft. Their rôle in naval warfare cannot yet be defined, because the machines themselves have not yet reached an advanced stage of development, and their probable performance cannot be forecast. There is no doubt, however, in the minds of naval men that the rôle of aircraft is to be important and distinguished.

CHAPTER III

NAVAL POWER

Mahan proved that sea power has exercised a determining influence on history. He proved that sea power has been necessary for commercial success in peace and military success in war. He proved that, while many wars have culminated with the victory of some army, the victory of some navy had been the previous essential. He proved that the immediate cause of success had often resulted inevitably from another cause, less apparent because more profound; that the operations of the navy had previously brought affairs up to the "mate in four moves," and that the final victory of the army was the resulting "checkmate."

Before Mahan proved his doctrine, it was felt in a general way that sea power was necessary to the prosperity and security of a nation. Mahan was not the first to have this idea, for it had been in the minds of some men, and in the policy of one nation, for more than a century. Neither was Mahan the first to put forth the idea in writing; but he was the first to make an absolute demonstration of the truth. Newton was not the first man to know, or to say,