But to insure all these fine results, both officers and men must be taught the art. Constant instruction and drilling are necessary, and in each navy a regular school of torpedo-practice is maintained, where the subject is studied in every way. In the United States such a school is kept at the Newport (R. I.) Torpedo Station, where the torpedoes themselves are fitted for use and supplied to the ships (the loaded war-heads are kept separately in the ship’s magazine), and where one or more torpedo-boats are reserved for drilling purposes. [Illustration: COPYRIGHT, 1897, BY C. E. BOLLES, BROOKLYN, N. Y. THE UNITED STATES BATTLE-SHIP “MAINE.” Blown up in the harbor of Havana, February 15, 1898.] But a worse and more insidious foe than even these sneaking, hiding, surface torpedo-boats threatens us in the submarine torpedo-boat, which inventors have been experimenting with since naval warfare first began. It is said that twenty-five hundred years ago divers were lowered into the water in a simply constructed air-box, to perforate the wooden bottom of an adversary’s war-galley and sink it. Again, in our Revolutionary War, a tiny walnut-shaped boat was made by an American, which was actually tried. It would hold one man, and air enough for him to breathe for half an hour. He would close the hatch, let in enough water to sink him a little way, and then scull himself along by means of a screw-bladed stern-oar until he got underneath the keel of an anchored vessel, to which, by ingenious means, he would attach a can of gunpowder to be fired by clockwork, giving him time to get away. It was actually tried and nearly succeeded. Robert Fulton, who made the first success of the steamboat, tried for years to contrive a submarine boat that would work, and succeeded so far as to scare British blockaders in 1812 very badly indeed; and the Confederates repeated the scare when the North was blockading their ports in the Civil War. The great advantage of a submarine boat is, of course, its invisibility, and its safety from shot even if discovered; but the difficulties of progress and control as to depth and direction under water, and at the same time effective appliance of the explosive and safe retreat, are so many that they have as yet been only partly overcome. If the thing is ever accomplished, naval warfare will be demoralized until some adequate means be found to combat this unseen, destroying agency. [Illustration: _Vesuvius_ in action.] The principal agent in submarine attacks would probably be some form of dynamite, which, inhuman as its use seems, is slowly but surely taking its place among the weapons of war. The United States has one vessel primarily designed to employ dynamite by hurling it in the form of shells. This volcanic craft is suitably named _Vesuvius_, and is a small, swift vessel having long tubes slanting upward through her forward deck, as shown in the illustration.